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Etabs Concrete Frame Design Manual

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This Technical Note presents some basic information and concepts helpful when performing concrete frame design using this program.

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									©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN

Contents

General Concrete Frame Design Information
1 General Design Information Design Codes Units Overwriting the Frame Design Procedure for a Concrete Frame Design Load Combinations Design of Beams Design of Columns Beam/Column Flexural Capacity Ratios Second Order P-Delta Effects Element Unsupported Lengths Analysis Sections and Design Sections Concrete Frame Design Process Concrete Frame Design Procedure Interactive Concrete Frame Design General Concrete Design Information Form Output Data Plotted Directly on the Model Overview Using the Print Design Tables Form Design Input Design Output 1-1 1-1 1-1 1-2 1-2 1-3 1-4 1-4 1-6 1-7

2

2-1

3

3-1 3-1

4

4-1 4-1 4-2 4-2

i

Concrete Frame Design Manual

Concrete Frame Design Specific to UBC97
5 General and Notation Introduction to the UBC 97 Series of Technical Notes Notation Preferences General Using the Preferences Form Preferences Overwrites General Overwrites Making Changes in the Overwrites Form Resetting Concrete Frame Overwrites to Default Values Design Load Combinations Strength Reduction Factors Column Design Overview Generation of Biaxial Interaction Surfaces Calculate Column Capacity Ratio Determine Factored Moments and Forces Determine Moment Magnification Factors Determine Capacity Ratio Required Reinforcing Area Design Column Shear Reinforcement Determine Required Shear Reinforcement Reference Beam Design Overview Design Beam Flexural Reinforcement Determine Factored Moments Determine Required Flexural Reinforcement 5-1 5-2

6

6-1 6-1 6-2

7

7-1 7-1 7-3 7-4

8 9 10

10-1 10-2 10-5 10-6 10-6 10-8 10-10 10-10 10-14 10-15

11

11-1 11-1 11-2 11-2

ii

Contents
Design Beam Shear Reinforcement 12 Joint Design Overview Determine the Panel Zone Shear Force Determine the Effective Area of Joint Check Panel Zone Shear Stress Beam/Column Flexural Capacity Ratios Input Data Input data Using the Print Design Tables Form Output Details Using the Print Design Tables Form 11-10

12-1 12-1 12-5 12-5 12-6

13

13-1 13-3

14

14-3

Concrete Frame Design Specific to ACI-318-99
15 General and Notation Introduction to the ACI318-99 Series of Technical Notes Notation Preferences General Using the Preferences Form Preferences Overwrites General Overwrites Making Changes in the Overwrites Form Resetting Concrete Frame Overwrites to Default Values Design Load Combinations Strength Reduction Factors 15-1 15-2

16

16-1 16-1 16-2

17

17-1 17-1 17-3 17-4

18 19

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Concrete Frame Design Manual

20

Column Design Overview Generation of Biaxial Interaction Surfaces Calculate Column Capacity Ratio Determine Factored Moments and Forces Determine Moment Magnification Factors Determine Capacity Ratio Required Reinforcing Area Design Column Shear Reinforcement Determine Section Forces Determine Concrete Shear Capacity Determine Required Shear Reinforcement References Beam Design Overview Design Beam Flexural Reinforcement Determine Factored Moments Determine Required Flexural Reinforcement Design for T-Beam Minimum Tensile Reinforcement Special Consideration for Seismic Design Design Beam Shear Reinforcement Determine Shear Force and Moment Determine Concrete Shear Capacity Determine Required Shear Reinforcement Joint Design Overview Determine the Panel Zone Shear Force Determine the Effective Area of Joint Check Panel Zone Shear Stress Beam/Column Flexural Capacity Ratios Input Data Input Data Using the Print Design Tables Form

20-1 20-2 20-5 20-6 20-6 20-9 20-10 20-10 20-11 20-12 20-13 20-15

21

21-1 21-1 21-2 21-2 21-5 21-8 21-8 21-9 21-11 21-12 21-13

22

22-1 22-1 22-4 22-4 22-6

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Contents

24

Output Details Using the Print Design Tables Form

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©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA JANUARY 2002

CONCRETE FRAME DESIGN

Technical Note 1 General Design Information
This Technical Note presents some basic information and concepts helpful when performing concrete frame design using this program.

Design Codes
The design code is set using the Options menu > Preferences > Concrete Frame Design command. You can choose to design for any one design code in any one design run. You cannot design some elements for one code and others for a different code in the same design run. You can, however, perform different design runs using different design codes without rerunning the analysis.

Units
For concrete frame design in this program, any set of consistent units can be used for input. You can change the system of units at any time. Typically, design codes are based on one specific set of units.

Overwriting the Frame Design Procedure for a Concrete Frame
The two design procedures possible for concrete beam design are: Concrete frame design No design If a line object is assigned a frame section property that has a concrete material property, its default design procedure is Concrete Frame Design. A concrete frame element can be switched between the Concrete Frame Design and the "None" design procedure. Assign a concrete frame element the "None" design procedure if you do not want it designed by the Concrete Frame Design postprocessor.

Design Codes

Technical Note 1 - 1

General Design Information

Concrete Frame Design

Change the default design procedure used for concrete frame elements by selecting the element(s) and clicking Design menu > Overwrite Frame Design Procedure. This change is only successful if the design procedure assigned to an element is valid for that element. For example, if you select a concrete element and attempt to change the design procedure to Steel Frame Design, the program will not allow the change because a concrete element cannot be changed to a steel frame element.

Design Load Combinations
The program creates a number of default design load combinations for concrete frame design. You can add in your own design load combinations. You can also modify or delete the program default load combinations. An unlimited number of design load combinations can be specified. To define a design load combination, simply specify one or more load cases, each with its own scale factor. For more information see Concrete Frame Design UBC97 Technical Note 8 Design Load Combination and Concrete Frame Design ACI 318-99 Technical Note 18 Design Load Combination.

Design of Beams
The program designs all concrete frame elements designated as beam sections in their Frame Section Properties as beams (see Define menu >Frame Sections command and click the Reinforcement button). In the design of concrete beams, in general, the program calculates and reports the required areas of steel for flexure and shear based on the beam moments, shears, load combination factors, and other criteria, which are described in detail in Concrete Frame UBC97 Technical Note Beam Design 11 and Concrete Frame ACI 318-99 Technical Note 21 Beam Design. The reinforcement requirements are calculated at each output station along the beam span. All the beams are designed for major direction flexure and shear only. Effects resulting from any axial forces, minor direction bending, and torsion that may exist in the beams must be investigated independently by the user. In designing the flexural reinforcement for the major moment at a particular section of a particular beam, the steps involve the determination of the maximum factored moments and the determination of the reinforcing steel.

Technical Note 1 - 2

Design Load Combinations

Concrete Frame Design

General Design Information

The beam section is designed for the maximum positive and maximum negative factored moment envelopes obtained from all of the load combinations. Negative beam moments produce top steel. In such cases, the beam is always designed as a rectangular section. Positive beam moments produce bottom steel. In such cases, the beam may be designed as a rectangular- or T-beam. For the design of flexural reinforcement, the beam is first designed as a singly reinforced beam. If the beam section is not adequate, the required compression reinforcement is calculated. In designing the shear reinforcement for a particular beam for a particular set of loading combinations at a particular station resulting from the beam major shear, the steps involve the determination of the factored shear force, the determination of the shear force that can be resisted by concrete, and the determination of the reinforcement steel required to carry the balance.

Design of Columns
The program designs all concrete frame elements designated as column sections in their Frame Section Properties as columns (see Define menu >Frame Sections command and click the Reinforcement button). In the design of the columns, the program calculates the required longitudinal steel, or if the longitudinal steel is specified, the column stress condition is reported in terms of a column capacity ratio. The capacity ratio is a factor that gives an indication of the stress condition of the column with respect to the capacity of the column. The design procedure for reinforced concrete columns involves the following steps: Generate axial force-biaxial moment interaction surfaces for all of the different concrete section types of the model. Check the capacity of each column for the factored axial force and bending moments obtained from each load combination at each end of the column. This step is also used to calculate the required reinforcement (if none was specified) that will produce a capacity ratio of 1.0. Design the column shear reinforcement. The shear reinforcement design procedure for columns is very similar to that for beams, except that the effect of the axial force on the concrete shear capacity needs to be considered. See Concrete Frame UBC97 Technical Note 10

Design of Beams

Technical Note 1 - 3

General Design Information

Concrete Frame Design

Column Design and Concrete Frame ACI 318-99 Technical Note 20 Column Design for more information.

Beam/Column Flexural Capacity Ratios
When the ACI 318-99 or UBC97 code is selected, the program calculates the ratio of the sum of the beam moment capacities to the sum of the column moment capacities at a particular joint for a particular column direction, major or minor. The capacities are calculated with no reinforcing overstrength factor, α, and including ϕ factors. The beam capacities are calculated for reversed situations and the maximum summation obtained is used. The moment capacities of beams that frame into the joint in a direction that is not parallel to the major or minor direction of the column are resolved along the direction that is being investigated and the resolved components are added to the summation. The column capacity summation includes the column above and the column below the joint. For each load combination, the axial force, Pu, in each of the columns is calculated from the program analysis load combinations. For each load combination, the moment capacity of each column under the influence of the corresponding axial load Pu is then determined separately for the major and minor directions of the column, using the uniaxial column interaction diagram. The moment capacities of the two columns are added to give the capacity summation for the corresponding load combination. The maximum capacity summations obtained from all of the load combinations is used for the beam/column capacity ratio. The beam/column flexural capacity ratios are only reported for Special Moment-Resisting Frames involving seismic design load combinations. See Beam/Column Flexural Capacity Ratios in Concrete Frame UBC97 Technical Note 12 Joint Design or in Concrete Frame ACI 318-99 Technical Note 22 Joint Design for more information.

Second Order P-Delta Effects
Typically, design codes require that second order P-Delta effects be considered when designing concrete frames. The P-Delta effects come from two sources. They are the global lateral translation of the frame and the local deformation of elements within the frame.

Technical Note 1 - 4

Second Order P-Delta Effects

Concrete Frame Design

General Design Information

∆

Original position of frame element shown by vertical line Position of frame element as a result of global lateral translation, ∆, shown by dashed line

δ

Final deflected position of frame element that includes the global lateral translation, ∆, and the local deformation of the element, δ

Figure 1: The Total Second Order P-Delta Effects on a Frame Element Caused by Both ∆ and δ
Consider the frame element shown in Figure 1, which is extracted from a story level of a larger structure. The overall global translation of this frame element is indicated by ∆. The local deformation of the element is shown as δ. The total second order P-Delta effects on this frame element are those caused by both ∆ and δ. The program has an option to consider P-Delta effects in the analysis. Controls for considering this effect are found using the Analyze menu > Set Analysis Options command and then clicking the Set P-Delta Parameters button. When you consider P-Delta effects in the analysis, the program does a good job of capturing the effect due to the ∆ deformation shown in Figure 1, but it does not typically capture the effect of the δ deformation (unless, in the model, the frame element is broken into multiple pieces over its length). In design codes, consideration of the second order P-Delta effects is generally achieved by computing the flexural design capacity using a formula similar to that shown in Equation. 1. MCAP where, MCAP = Flexural design capacity = aMnt + bMlt Eqn. 1

Second Order P-Delta Effects

Technical Note 1 - 5

General Design Information

Concrete Frame Design

Mnt

=

Required flexural capacity of the member assuming there is no translation of the frame (i.e., associated with the δ deformation in Figure 1) Required flexural capacity of the member as a result of lateral translation of the frame only (i.e., associated with the ∆ deformation in Figure 1) Unitless factor multiplying Mnt Unitless factor multiplying Mlt (assumed equal to 1 by the program; see below)

Mlt

=

a b

= =

When the program performs concrete frame design, it assumes that the factor b is equal to 1 and it uses code-specific formulas to calculate the factor a. That b = 1 assumes that you have considered P-Delta effects in the analysis, as previously described. Thus, in general, if you are performing concrete frame design in this program, you should consider P-Delta effects in the analysis before running the design.

Element Unsupported Lengths
The column unsupported lengths are required to account for column slenderness effects. The program automatically determines these unsupported lengths. They can also be overwritten by the user on an element-by-element basis, if desired, using the Design menu > Concrete Frame Design > View/Revise Overwrites command. There are two unsupported lengths to consider. They are L33 and L22, as shown in Figure 2. These are the lengths between support points of the element in the corresponding directions. The length L33 corresponds to instability about the 3-3 axis (major axis), and L22 corresponds to instability about the 2-2 axis (minor axis). The length L22 is also used for lateral-torsional buckling caused by major direction bending (i.e., about the 3-3 axis). In determining the values for L22 and L33 of the elements, the program recognizes various aspects of the structure that have an effect on these lengths, such as member connectivity, diaphragm constraints and support points. The program automatically locates the element support points and evaluates the corresponding unsupported length.

Technical Note 1 - 6

Element Unsupported Lengths

Concrete Frame Design

General Design Information

Figure 2: Major and Minor Axes of Bending
It is possible for the unsupported length of a frame element to be evaluated by the program as greater than the corresponding element length. For example, assume a column has a beam framing into it in one direction, but not the other, at a floor level. In this case, the column is assumed to be supported in one direction only at that story level, and its unsupported length in the other direction will exceed the story height.

Analysis Sections and Design Sections
Analysis sections are those section properties used to analyze the model when you click the Analyze menu > Run Analysis command. The design section is whatever section has most currently been designed and thus designated the current design section. Tip: It is important to understand the difference between analysis sections and design sections.

Analysis Sections and Design Sections

Technical Note 1 - 7

General Design Information

Concrete Frame Design

It is possible for the last used analysis section and the current design section to be different. For example, you may have run your analysis using a W18X35 beam and then found in the design that a W16X31 beam worked. In that case, the last used analysis section is the W18X35 and the current design section is the W16X31. Before you complete the design process, verify that the last used analysis section and the current design section are the same. The Design menu > Concrete Frame Design > Verify Analysis vs Design Section command is useful for this task. The program keeps track of the analysis section and the design section separately. Note the following about analysis and design sections: Assigning a beam a frame section property using the Assign menu > Frame/Line > Frame Section command assigns the section as both the analysis section and the design section. Running an analysis using the Analyze menu > Run Analysis command (or its associated toolbar button) always sets the analysis section to be the same as the current design section. Assigning an auto select list to a frame section using the Assign menu > Frame/Line > Frame Section command initially sets the design section to be the beam with the median weight in the auto select list. Unlocking a model deletes the design results, but it does not delete or change the design section. Using the Design menu > Concrete Frame Design > Select Design Combo command to change a design load combination deletes the design results, but it does not delete or change the design section. Using the Define menu > Load Combinations command to change a design load combination deletes the design results, but it does not delete or change the design section. Using the Options menu > Preferences > Concrete Frame Design command to change any of the composite beam design preferences deletes the design results, but it does not delete or change the design section. Deleting the static nonlinear analysis results also deletes the design results for any load combination that includes static nonlinear forces. Typically,

Technical Note 1 - 8

Analysis Sections and Design Sections

Concrete Frame Design

General Design Information

static nonlinear analysis and design results are deleted when one of the following actions is taken: Use the Define menu > Frame Nonlinear Hinge Properties command to redefine existing or define new hinges. Use the Define menu > Static Nonlinear/Pushover Cases command to redefine existing or define new static nonlinear load cases. Use the Assign menu > Frame/Line > Frame Nonlinear Hinges command to add or delete hinges. Again, note that these actions delete only results for load combinations that include static nonlinear forces.

Analysis Sections and Design Sections

Technical Note 1 - 9

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN

Technical Note 2 Concrete Frame Design Process
This Technical Note describes a basic concrete frame design process using this program. Although the exact steps you follow may vary, the basic design process should be similar to that described herein. Other Technical Notes in the Concrete Frame Design series provide additional information, including the distinction between analysis sections and design sections (see Analysis Sections and Design Sections in Concrete Frame Design Technical Note 1 General Design Information). The concrete frame design postprocessor can design or check concrete columns and can design concrete beams. Important note: A concrete frame element is designed as a beam or a column, depending on how its frame section property was designated when it was defined using the Define menu > Frame Sections command. Note that when using this command, after you have specified that a section has a concrete material property, you can click on the Reinforcement button and specify whether it is a beam or a column.

Concrete Frame Design Procedure
The following sequence describes a typical concrete frame design process for a new building. Note that although the sequence of steps you follow may vary, the basic process probably will be essentially the same. 1. Use the Options menu > Preferences > Concrete Frame Design command to choose the concrete frame design code and to review other concrete frame design preferences and revise them if necessary. Note that default values are provided for all concrete frame design preferences, so it is unnecessary to define any preferences unless you want to change some of the default values. See Concrete Frame Design ACI UBC97 Technical Notes 6 Preferences and Concrete Frame Design ACI 318-99 Technical Notes 16 Preferences for more information.

Concrete Frame Design Procedure

Technical Note 2 - 1

Concrete Frame Design Process

Concrete Frame Design

2. 3.

Create the building model. Run the building analysis using the Analyze menu > Run Analysis command. Assign concrete frame overwrites, if needed, using the Design menu > Concrete Frame Design > View/Revise Overwrites command. Note that you must select frame elements before using this command. Also note that default values are provided for all concrete frame design overwrites, so it is unnecessary to define any overwrites unless you want to change some of the default values. Note that the overwrites can be assigned before or after the analysis is run. See Concrete Frame Design UBC97 Technical Note 7 Overwrites and Concrete Frame Design ACI 318-99 Technical Note 17 Overwrites for more information. To use any design load combinations other than the defaults created by the program for your concrete frame design, click the Design menu > Concrete Frame Design > Select Design Combo command. Note that you must have already created your own design combos by clicking the Define menu > Load Combinations command. See Concrete Frame Design UBC97 Technical Note 8 Design Load Combinations and Concrete Frame Design ACI 318-99 Technical Note 18 Design Load Combinations for more information. Click the Design menu > Concrete Frame Design > Start Design/Check of Structure command to run the concrete frame design. Review the concrete frame design results by doing one of the following: a. Click the Design menu > Concrete Frame Design > Display Design Info command to display design input and output information on the model. See Concrete Frame Design Technical Note 4 Output Data Plotted Directly on the Model for more information. b. Right click on a frame element while the design results are displayed on it to enter the interactive design mode and interactively design the frame element. Note that while you are in this mode, you can revise overwrites and immediately see the results of the new design. See Concrete Frame Design Technical Note 3 Interactive Concrete Frame Design for more information.

4.

5.

6.

7.

Technical Note 2 - 2

Concrete Frame Design Procedure

Concrete Frame Design

Concrete Frame Design Process

If design results are not currently displayed (and the design has been run), click the Design menu > Concrete Frame Design > Interactive Concrete Frame Design command and then right click a frame element to enter the interactive design mode for that element. 8. Use the File menu > Print Tables > Concrete Frame Design command to print concrete frame design data. If you select frame elements before using this command, data is printed only for the selected elements. See Concrete Frame Design UBC97 Technical Note 14 Output Details and Concrete Frame Design ACI 318-99 Technical Note 24 Output Details for more information. Use the Design menu > Concrete Frame Design > Change Design Section command to change the design section properties for selected frame elements. Click the Design menu > Concrete Frame Design > Start Design/Check of Structure command to rerun the concrete frame design with the new section properties. Review the results using the procedures described in Item 7. Rerun the building analysis using the Analyze menu > Run Analysis command. Note that the section properties used for the analysis are the last specified design section properties. Click the Design menu > Concrete Frame Design > Start Design/Check of Structure command to rerun the concrete frame design with the new analysis results and new section properties. Review the results using the procedures described above. Again use the Design menu > Concrete Frame Design > Change Design Section command to change the design section properties for selected frame elements, if necessary. Repeat the processes in steps 10, 11 and 12 as many times as necessary. Rerun the building analysis using the Analyze menu > Run Analysis command. Note that the section properties used for the analysis are the last specified design section properties.

9.

10.

11.

12.

13.

14.

15.

Concrete Frame Design Procedure

Technical Note 2 - 3

Concrete Frame Design Process

Concrete Frame Design

Note: Concrete frame design is an iterative process. Typically, the analysis and design will be rerun multiple times to complete a design. 16. Click the Design menu > Concrete Frame Design > Start Design/Check of Structure command to rerun the concrete frame design with the new section properties. Review the results using the procedures described in Item 7. Click the Design menu > Concrete Frame Design > Verify Analysis vs Design Section command to verify that all of the final design sections are the same as the last used analysis sections. Use the File menu > Print Tables > Concrete Frame Design command to print selected concrete frame design results, if desired.

17.

18.

It is important to note that design is an iterative process. The sections used in the original analysis are not typically the same as those obtained at the end of the design process. Always run the building analysis using the final frame section sizes and then run a design check using the forces obtained from that analysis. Use the Design menu > Concrete Frame Design > Verify Analysis vs Design Section command to verify that the design sections are the same as the analysis sections.

Technical Note 2 - 4

Concrete Frame Design Procedure

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN

Technical Note 3

Interactive Concrete Frame Design
This Technical Note describes interactive concrete frame design and review, which is a powerful mode that allows the user to review the design results for any concrete frame design and interactively revise the design assumptions and immediately review the revised results.

General
Note that a design must have been run for the interactive design mode to be available. To run a design, click the Design menu > Concrete Frame Design > Start Design/Check of Structure command. Right click on a frame element while the design results are displayed on it to enter the interactive design mode and interactively design the element in the Concrete Design Information form. If design results are not currently displayed (and a design has been run), click the Design menu > Concrete Frame Design > Interactive Concrete Frame Design command and then right click a frame element to enter the interactive design mode for that element. Important note: A concrete frame element is designed as a beam or a column, depending on how its frame section property was designated when it was defined using the Define menu > Frame Sections command and the Reinforcement button, which is only available if it is a concrete section.

Concrete Design Information Form
Table 1 describe the features that are included in the Concrete Design Information form.

General

Technical Note 3 - 1

Interactive Concrete Frame Design

Concrete Frame Design

Table 1 Concrete Design Information Form
Item Story Beam DESCRIPTION This is the story level ID associated with the frame element. This is the label associated with a frame element that has been assigned a concrete frame section property that is designated as a beam. See the important note previously in this Technical Note for more information. This is the label associated with a frame element that has been assigned a concrete frame section property that is designated as a column. See the important note previously in this Technical Note for more information. This is the label associated with a frame element that has been assigned a concrete frame section property.

Column

Section Name

Reinforcement Information The reinforcement information table on the Concrete Design Information form shows the output information obtained for each design load combination at each output station along the frame element. For columns that are designed by this program, the item with the largest required amount of longitudinal reinforcing is initially highlighted. For columns that are checked by this program, the item with the largest capacity ratio is initially highlighted. For beams, the item with the largest required amount of bottom steel is initially highlighted. Following are the possible headings in the table: Combo ID Station location Longitudinal reinforcement Capacity ratio This is the name of the design load combination considered. This is the location of the station considered, measured from the i-end of the frame element. This item applies to columns only. It also only applies to columns for which the program designs the longitudinal reinforcing. It is the total required area of longitudinal reinforcing steel. This item applies to columns only. It also only applies to columns for which you have specified the location and size of reinforcing bars and thus the program checks the design. This item is the capacity ratio.

Technical Note 3 - 2

Table 1 Concrete Design Information Form

Concrete Frame Design

Interactive Concrete Frame Design

Table 1 Concrete Design Information Form
Item DESCRIPTION The capacity ratio is determined by first extending a line from the origin of the PMM interaction surface to the point representing the P, M2 and M3 values for the designated load combination. Assume the length of this first line is designated L1. Next, a second line is extended from the origin of the PMM interaction surface through the point representing the P, M2 and M3 values for the designated load combination until it intersects the interaction surface. Assume the length of this line from the origin to the interaction surface is designated L2. The capacity ratio is equal to L1/L2. Major shear reinforcement Minor shear reinforcement Top steel Bottom steel Shear steel This item applies to columns only. It is the total required area of shear reinforcing per unit length for shear acting in the column major direction. This item applies to columns only. It is the total required area of shear reinforcing per unit length for shear acting in the column minor direction. This item applies to beams only. It is the total required area of longitudinal top steel at the specified station. This item applies to beams only. It is the total required area of longitudinal bottom steel at the specified station. This item applies to beams only. It is the total required area of shear reinforcing per unit length at the specified station for loads acting in the local 2-axis direction of the beam. Click this button to access and make revisions to the concrete frame overwrites and then immediately see the new design results. If you modify some overwrites in this mode and you exit both the Concrete Frame Design Overwrites form and the Concrete Design Information form by clicking their respective OK buttons, the changes to the overwrites are saved permanently. When you exit the Concrete Frame Design Overwrites form by clicking the OK button the changes are temporarily saved. If you then exit the Concrete Design Information form by clicking the Cancel button the changes you made to the concrete frame overwrites are considered temporary only and are not permanently saved. Permanent saving of the overwrites does not actually occur until you click the OK button in the Concrete Design Information form as well as the Concrete Frame Design Overwrites form.

Overwrites Button

Table 1 Concrete Design Information Form

Technical Note 3 - 3

Interactive Concrete Frame Design

Concrete Frame Design

Table 1 Concrete Design Information Form
Item Details Button DESCRIPTION Clicking this button displays design details for the frame element. Print this information by selecting Print from the File menu that appears at the top of the window displaying the design details. Clicking this button displays the biaxial interaction curve for the concrete section at the location in the element that is highlighted in the table.

Interaction Button

Technical Note 3 - 4

Table 1 Concrete Design Information Form

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN

Technical Note 4 Output Data Plotted Directly on the Model
This Technical Note describes the input and output data that can be plotted directly on the model.

Overview
Use the Design menu > Concrete Frame Design > Display Design Info command to display on-screen output plotted directly on the program model. If desired, the screen graphics can then be printed using the File menu > Print Graphics command. The on-screen display data presents input and output data.

Using the Print Design Tables Form
To print the concrete frame input summary directly to a printer, use the File menu > Print Tables > Concrete Frame Design command and click the check box on the Print Design Tables form. Click the OK button to send the print to your printer. Click the Cancel button rather than the OK button to cancel the print. Use the File menu > Print Setup command and the Setup>> button to change printers, if necessary. To print the concrete frame input summary to a file, click the Print to File check box on the Print Design Tables form. Click the Filename>> button to change the path or filename. Use the appropriate file extension for the desired format (e.g., .txt, .xls, .doc). Click the OK buttons on the Open File for Printing Tables form and the Print Design Tables form to complete the request. Note: The File menu > Display Input/Output Text Files command is useful for displaying output that is printed to a text file. The Append check box allows you to add data to an existing file. The path and filename of the current file is displayed in the box near the bottom of the Print Design Tables form. Data will be added to this file. Or use the Filename

Overview

Technical Note 4 - 1

Output Data Plotted Directly on the Model

Concrete Frame Design

button to locate another file, and when the Open File for Printing Tables caution box appears, click Yes to replace the existing file. If you select a specific concrete frame element(s) before using the File menu > Print Tables > concrete Frame Design command, the Selection Only check box will be checked. The print will be for the selected steel frame element(s) only.

Design Input
The following types of data can be displayed directly on the model by selecting the data type (shown in bold type) from the drop-down list on the Display Design Results form. Display this form by selecting he Design menu > Concrete Frame Design > Display Design Info command. Design Sections Design Type Live Load Red Factors Unbraced L_Ratios Eff Length K-Factors Cm Factors DNS Factors DS Factors Each of these items is described in the code-specific Concrete Frame Design UBC97 Technical Note 13 Input Data and Concrete Frame Design ACI 318-99 Technical Note 23 Input Data.

Design Output
The following types of data can be displayed directly on the model by selecting the data type (shown in bold type) from the drop-down list on the Display Design Results form. Display this form by selecting he Design menu > Concrete Frame Design > Display Design Info command.

Technical Note 4 - 2

Design Input

Concrete Frame Design

Output Data Plotted Directly on the Model

Longitudinal Reinforcing Shear Reinforcing Column Capacity Ratios Joint Shear Capacity Ratios Beam/Column Capacity Ratios Each of these items is described in the code-specific Concrete Frame Design ACI 318-99 Technical Note 24 Output Details and Concrete Frame Design UBC97 Technical Note 14 Output Details.

Design Output

Technical Note 4 - 3

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN UBC97

Technical Note 5

General and Notation Introduction to the UBC97 Series of Technical Notes
The Concrete Frame Design UBC97 series of Technical Notes describes in detail the various aspects of the concrete design procedure that is used by this program when the user selects the UBC97 Design Code (ICBO 1997). The various notations used in this series are listed herein. The design is based on user-specified loading combinations. The program provides a set of default load combinations that should satisfy requirements for the design of most building type structures. See Concrete Frame Design UBC97 Technical Note 8 Design Load Combinations for more information. When using the UBC 97 option, a frame is assigned to one of the following five Seismic Zones (UBC 2213, 2214): Zone 0 Zone 1 Zone 2 Zone 3 Zone 4 By default the Seismic Zone is taken as Zone 4 in the program. However, the Seismic Zone can be overwritten in the Preference form to change the default. See Concrete Frame Design UBC97 Technical Note 6 Preferences for more information. When using the UBC 97 option, the following Framing Systems are recognized and designed according to the UBC design provisions (UBC 1627, 1921): Ordinary Moment-Resisting Frame (OMF)

General and Notation

Technical Note 5 - 1

General and Notation

Concrete Frame Design UBC97

Intermediate Moment-Resisting Frame (IMRF) Special Moment-Resisting Frame (SMRF) The Ordinary Moment-Resisting Frame (OMF) is appropriate in minimal seismic risk areas, especially in Seismic Zones 0 and 1. The Intermediate Moment-Resisting Frame (IMRF) is appropriate in moderate seismic risk areas, specially in Seismic Zone 2. The Special Moment-Resisting Frame (SMRF) is appropriate in high seismic risk areas, specially in Seismic Zones 3 and 4. The UBC seismic design provisions are considered in the program. The details of the design criteria used for the different framing systems are described in Concrete Frame Design UBC97 Technical Note 9 Strength Reduction Factors, Concrete Frame Design UBC97 Technical Note 10 Column Design, Concrete Frame Design UBC97 Technical Note 11 Beam Design, and Concrete Frame Design UBC97 Technical Note 12 Joint Design. By default the frame type is taken in the program as OMRF in Seismic Zone 0 and 1, as IMRF in Seismic Zone 2, and as SMRF in Seismic Zone 3 and 4. However, the frame type can be overwritten in the Overwrites form on a member-by-member basis. See Concrete Frame Design UBC97 Technical Note 7 Overwrites for more information. If any member is assigned with a frame type, the change of the Seismic Zone in the Preferences will not modify the frame type of an individual member that has been assigned a frame type. The program also provides input and output data summaries, which are described in Concrete Frame Design UBC97 Technical Note 13 Input Data and Concrete Frame Design UBC97 Technical Note 14 Output Details. English as well as SI and MKS metric units can be used for input. The code is based on Inch-Pound-Second units. For simplicity, all equations and descriptions presented in this Technical Note correspond to Inch-Pound-Second units unless otherwise noted.

Notation
Acv Ag As Area of concrete used to determine shear stress, sq-in Gross area of concrete, sq-in Area of tension reinforcement, sq-in

Technical Note 5 - 2

General and Notation

Concrete Frame Design UBC97

General and Notation

' As

Area of compression reinforcement, sq-in Area of steel required for tension reinforcement, sq-in Total area of column longitudinal reinforcement, sq-in Area of shear reinforcement, sq-in Coefficient, dependent upon column curvature, used to calculate moment magnification factor Diameter of hoop, in Modulus of elasticity of concrete, psi Modulus of elasticity of reinforcement, assumed as 29,000,000 psi (UBC 1980.5.2) Moment of inertia of gross concrete section about centroidal axis, neglecting reinforcement, in4 Moment of inertia of reinforcement about centroidal axis of member cross section, in4 Clear unsupported length, in Smaller factored end moment in a column, lb-in Larger factored end moment in a column, lb-in Factored moment to be used in design, lb-in Nonsway component of factored end moment, lb-in Sway component of factored end moment, lb-in Factored moment at section, lb-in Factored moment at section about X-axis, lb-in Factored moment at section about Y-axis, lb-in Axial load capacity at balanced strain conditions, lb

As(required) Ast Av Cm

D' Ec Es

Ig

Ise

L M1 M2 Mc Mns Ms Mu Mux Muy Pb

General and Notation

Technical Note 5 - 3

General and Notation

Concrete Frame Design UBC97

Pc Pmax P0 Pu Vc VE VD+L Vu Vp a ab b bf bw c cb d d' ds f c' fy

Critical buckling strength of column, lb Maximum axial load strength allowed, lb Acial load capacity at zero eccentricity, lb Factored axial load at section, lb Shear resisted by concrete, lb Shear force caused by earthquake loads, lb Shear force from span loading, lb Factored shear force at a section, lb Shear force computed from probable moment capacity, lb Depth of compression block, in Depth of compression block at balanced condition, in Width of member, in Effective width of flange (T-Beam section), in Width of web (T-Beam section), in Depth to neutral axis, in Depth to neutral axis at balanced conditions, in Distance from compression face to tension reinforcement, in Concrete cover to center of reinforcing, in Thickness of slab (T-Beam section), in Specified compressive strength of concrete, psi Specified yield strength of flexural reinforcement, psi fy ≤ 80,000 psi (UBC 1909.4)

Technical Note 5 - 4

General and Notation

Concrete Frame Design UBC97

General and Notation

fys h k r

Specified yield strength of flexural reinforcement, psi Dimension of column, in Effective length factor Radius of gyration of column section, in Reinforcing steel overstrength factor Factor for obtaining depth of compression block in concrete Absolute value of ratio of maximum factored axial dead load to maximum factored axial total load Moment magnification factor for sway moments Moment magnification factor for nonsway moments Strain in concrete Strain in reinforcing steel Strength reduction factor

α β1 βd δs δns εc εs ϕ

General and Notation

Technical Note 5 - 5

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN UBC97

Technical Note 6 Preferences
This Technical Note describes the items in the Preferences form.

General
The concrete frame design preferences in this program are basic assignments that apply to all concrete frame elements. Use the Options menu > Preferences > Concrete Frame Design command to access the Preferences form where you can view and revise the concrete frame design preferences. Default values are provided for all concrete frame design preference items. Thus, it is not required that you specify or change any of the preferences. You should, however, at least review the default values for the preference items to make sure they are acceptable to you.

Using the Preferences Form
To view preferences, select the Options menu > Preferences > Concrete Frame Design. The Preferences form will display. The preference options are displayed in a two-column spreadsheet. The left column of the spreadsheet displays the preference item name. The right column of the spreadsheet displays the preference item value. To change a preference item, left click the desired preference item in either the left or right column of the spreadsheet. This activates a drop-down box or highlights the current preference value. If the drop-down box appears, select a new value. If the cell is highlighted, type in the desired value. The preference value will update accordingly. You cannot overwrite values in the dropdown boxes. When you have finished making changes to the concrete frame preferences, click the OK button to close the form. You must click the OK button for the changes to be accepted by the program. If you click the Cancel button to exit

General

Technical Note 6 - 1

Preferences

Concrete Frame Design UBC97

the form, any changes made to the preferences are ignored and the form is closed.

Preferences
For purposes of explanation in this Technical Note, the preference items are presented in Table 1. The column headings in the table are described as follows: Item: The name of the preference item as it appears in the cells at the left side of the Preferences form. Possible Values: The possible values that the associated preference item can have. Default Value: The built-in default value that the program assumes for the associated preference item. Description: A description of the associated preference item.

Table 1: Concrete Frame Preferences
Item Design Code Possible Values Any code in the program >0 >0 >0 >0 ≥4.0 Default Value UBC97 Description Design code used for design of concrete frame elements. Unitless strength reduction factor per UBC 1909. Unitless strength reduction factor per UBC 1909. Unitless strength reduction factor per UBC 1909. Unitless strength reduction factor per UBC 1909. Number of equally spaced interaction curves used to create a full 360-degree interaction surface (this item should be a multiple of four). We recommend that you use 24 for this item.

Phi Bending Tension Phi Compression Tied Phi Compression Spiral Phi Shear Number Interaction Curves

0.9 0.7 0.75 0.85 24

Technical Note 6 - 2

Preferences

Concrete Frame Design UBC97

Preferences

Table 1: Concrete Frame Preferences
Item Possible Values Default Value 11 Description Number of points used for defining a single curve in a concrete frame interaction surface (this item should be odd). Toggle for design load combinations that include a time history designed for the envelope of the time history, or designed step-by-step for the entire time history. If a single design load combination has more than one time history case in it, that design load combination is designed for the envelopes of the time histories, regardless of what is specified here.

Number Inter- Any odd value action Points ≥1.0

Time History Design

Envelopes or Step-by-Step

Envelopes

Preferences

Technical Note 6 - 3

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN UBC97

Technical Note 7

Overwrites General
The concrete frame design overwrites are basic assignments that apply only to those elements to which they are assigned. This Technical Note describes concrete frame design overwrites for UBC97. To access the overwrites, select an element and click the Design menu > Concrete Frame Design > View/Revise Overwrites command. Default values are provided for all overwrite items. Thus, you do not need to specify or change any of the overwrites. However, at least review the default values for the overwrite items to make sure they are acceptable. When changes are made to overwrite items, the program applies the changes only to the elements to which they are specifically assigned; that is, to the elements that are selected when the overwrites are changed.

Overwrites
For explanation purposes in this Technical Note, the overwrites are presented in Table 1. The column headings in the table are described as follows. Item: The name of the overwrite item as it appears in the program. To save space in the formes, these names are generally short. Possible Values: The possible values that the associated overwrite item can have. Default Value: The default value that the program assumes for the associated overwrite item. Description: A description of the associated overwrite item. An explanation of how to change an overwrite is provided at the end of this Technical Note.

Overwrites

Technical Note 7 - 1

Overwrites

Concrete Frame Design UBC97

Table 1 Concrete Frame Design Overwrites
Item Element Section Sway Special, Sway Special Frame type; see UBC 1910.11 to 1910.13. Sway Intermediate, Sway Ordinary NonSway >0 ≤1.0 >0 ≤1.0 >0 ≤1.0 >0 ≤1.0 >0 ≤1.0 >0 ≤1.0 >0 ≤1.0 >0 ≤1.0 >0 ≤1.0 1 1 1 See UBC 1910.12.3.1 relates actual moment diagram to an equivalent uniform moment diagram. See UBC 1910.12.3.1 relates actual moment diagram to an equivalent uniform moment diagram. See UBC 1910.12. 1 See UBC 1910.12.1. 1 See UBC 1910.12.1. 1.0 1.0 1. 1. Used to reduce the live load contribution to the factored loading. Possible Values Default Value Description

Element Type

Live Load Reduction Factor Horizontal Earthquake Factor Unbraced Length Ratio (Major) Unbraced Length Ratio (Minor) Effective Length Factor (K Major) Effective Length Factor (K Minor) Moment Coefficient (Cm Major) Moment Coefficient (Cm Minor) NonSway Moment Factor (Dns Major)

Technical Note 7 - 2

Overwrites

Concrete Frame Design UBC97

Overwrites

Table 1 Concrete Frame Design Overwrites
Item NonSway Moment Factor (Dns Minor) Sway Moment Factor (Ds Major) Sway Moment Factor (Ds Minor) Possible Values Default Value 1 Description See UBC 1910.12.

1

See UBC 1910.12.

1

See UBC 1910.12.

Making Changes in the Overwrites Form
To access the concrete frame overwrites, select an element and click the Design menu > Concrete Frame Design > View/Revise Overwrites command. The overwrites are displayed in the form with a column of check boxes and a two-column spreadsheet. The left column of the spreadsheet contains the name of the overwrite item. The right column of the spreadsheet contains the overwrites values. Initially, the check boxes in the Concrete Frame Design Overwrites form are all unchecked and all of the cells in the spreadsheet have a gray background to indicate that they are inactive and the items in the cells cannot be changed. The names of the overwrite items are displayed in the first column of the spreadsheet. The values of the overwrite items are visible in the second column of the spreadsheet if only one element was selected before the overwrites form was accessed. If multiple elements were selected, no values show for the overwrite items in the second column of the spreadsheet. After selecting one or multiple elements, check the box to the left of an overwrite item to change it. Then left click in either column of the spreadsheet to activate a drop-down box or highlight the contents in the cell in the right column of the spreadsheet. If the drop-down box appears, select a value from

Overwrites

Technical Note 7 - 3

Overwrites

Concrete Frame Design UBC97

the box. If the cell contents is highlighted, type in the desired value. The overwrite will reflect the change. You cannot change the values of the dropdown boxes. When changes to the overwrites have been completed, click the OK button to close the form. The program then changes all of the overwrite items whose associated check boxes are checked for the selected members. You must click the OK button for the changes to be accepted by the program. If you click the Cancel button to exit the form, any changes made to the overwrites are ignored and the form is closed.

Resetting Concrete Frame Overwrites to Default Values
Use the Design menu > Concrete Frame Design > Reset All Overwrites command to reset all of the steel frame overwrites. All current design results will be deleted when this command is executed. Important note about resetting overwrites: The program defaults for the overwrite items are built into the program. The concrete frame overwrite values that were in a .edb file that you used to initialize your model may be different from the built-in program default values. When you reset overwrites, the program resets the overwrite values to its built-in values, not to the values that were in the .edb file used to initialize the model.

Technical Note 7 - 4

Overwrites

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN UBC97

Technical Note 8

Design Load Combinations
The design load combinations are the various combinations of the prescribed load cases for which the structure needs to be checked. For the UBC 97 code, if a structure is subjected to dead load (DL) and live load (LL) only, the stress check may need only one load combination, namely 1.4 DL + 1.7 LL (UBC 1909.2.1). However, in addition to the dead and live loads, if the structure is subjected to wind (WL) and earthquake (EL) loads, and considering that wind and earthquake forces are reversible, the following load combinations may need to be considered (UBC 1909.2). 1.4 DL 1.4 DL + 1.7 LL 0.9 DL ± 1.3 WL 0.75 (1.4 DL + 1.7 LL ± 1.7 WL) 0.9 DL ± 1.0 EL 1.2 DL + 0.5 LL ± 1.0 EL) (UBC 1909.2.1) (UBC 1909.2.1) (UBC 1909.2.2) (UBC 1909.2.2) (UBC 1909.2.3, 1612.2.1) (UBC 1909.2.3, 1612.2.1)

These are also the default design load combinations in the program whenever the UBC97 code is used. Live load reduction factors can be applied to the member forces of the live load condition on an element-by-element basis to reduce the contribution of the live load to the factored loading. See Concrete Frame Design UBC97 Technical Note 7 Overwrites for more information.

Design Load Combinations

Technical Note 8 - 1

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN UBC97

Technical Note 9

Strength Reduction Factors
The strength reduction factors, ϕ, are applied on the nominal strength to obtain the design strength provided by a member. The ϕ factors for flexure, axial force, shear, and torsion are as follows: ϕ ϕ ϕ ϕ = 0.90 for flexure = 0.90 for axial tension = 0.90 for axial tension and flexure (UBC 1909.3.2.1) (UBC 1909.3.2.2) (UBC 1909.3.2.2)

= 0.75 for axial compression, and axial compression and flexure (spirally reinforced column) (UBC 1909.3.2.2) = 0.70 for axial compression, and axial compression and flexure (tied column) (UBC 1909.3.2.2) = 0.85 for shear and torsion (non-seismic design) = 0.60 for shear and torsion (UBC 1909.3.2.3) (UBC 1909.3.2.3)

ϕ

ϕ ϕ

Strength Reduction Factors

Technical Note 9 - 1

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN UBC97

Technical Note 10

Column Design
This Technical Note describes how the program checks column capacity or designs reinforced concrete columns when the UBC97 code is selected.

Overview
The program can be used to check column capacity or to design columns. If you define the geometry of the reinforcing bar configuration of each concrete column section, the program will check the column capacity. Alternatively, the program can calculate the amount of reinforcing required to design the column. The design procedure for the reinforced concrete columns of the structure involves the following steps: Generate axial force/biaxial moment interaction surfaces for all of the different concrete section types of the model. A typical biaxial interaction surface is shown in Figure 1. When the steel is undefined, the program generates the interaction surfaces for the range of allowable reinforcement1 to 8 percent for Ordinary and Intermediate moment resisting frames (UBC 1910.9.1) and 1 to 6 percent for Special moment resisting frames (UBC 1921.4.3.1). Calculate the capacity ratio or the required reinforcing area for the factored axial force and biaxial (or uniaxial) bending moments obtained from each loading combination at each station of the column. The target capacity ratio is taken as 1 when calculating the required reinforcing area. Design the column shear reinforcement. The following four subsections describe in detail the algorithms associated with this process.

Overview

Technical Note 10 - 1

Column Design

Concrete Frame Design UBC97

Figure 1 A Typical Column Interaction Surface

Generation of Biaxial Interaction Surfaces
The column capacity interaction volume is numerically described by a series of discrete points that are generated on the three-dimensional interaction failure surface. In addition to axial compression and biaxial bending, the formulation allows for axial tension and biaxial bending considerations. A typical interaction diagram is shown in Figure 1.

Technical Note 10 - 2

Generation of Biaxial Interaction Surfaces

Concrete Frame Design UBC97

Column Design

The coordinates of these points are determined by rotating a plane of linear strain in three dimensions on the section of the column. See Figure 2. The linear strain diagram limits the maximum concrete strain, εc, at the extremity of the section, to 0.003 (UBC 1910.2.3). The formulation is based consistently upon the general principles of ultimate strength design (UBC 1910.3), and allows for any doubly symmetric rectangular, square, or circular column section. The stress in the steel is given by the product of the steel strain and the steel modulus of elasticity, εsEs, and is limited to the yield stress of the steel, fy (UBC 1910.2.4). The area associated with each reinforcing bar is assumed to be placed at the actual location of the center of the bar and the algorithm does not assume any further simplifications with respect to distributing the area of steel over the cross section of the column, such as an equivalent steel tube or cylinder. See Figure 3. The concrete compression stress block is assumed to be rectangular, with a stress value of 0.85 f c' (UBC 1910.2.7.1). See Figure 3. The interaction algorithm provides correction to account for the concrete area that is displaced by the reinforcement in the compression zone. The effects of the strength reduction factor, ϕ, are included in the generation of the interaction surfaces. The maximum compressive axial load is limited to ϕPn(max), where ϕPn(max) = 0.85ϕ[0.85 f c' (Ag-Ast)+fyAst] (spiral) ϕPn(max) = 0.85ϕ[0.85 f c' (Ag-Ast)+fyAst] (tied) ϕ ϕ = 0.70 for tied columns = 0.75 for spirally reinforced columns (UBC 1910.3.5.1) (UBC 1910.3.5.2) (UBC 1909.3.2.2) (UBC 1909.3.2.2)

The value of ϕ used in the interaction diagram varies from ϕmin to 0.9 based on the axial load. For low values of axial load, ϕ is increased linearly from ϕmin to 0.9 as the nominal capacity ϕPn decreases from the smaller of ϕPb or 0.1 f c' Ag to zero, where Pb is the axial force at the balanced condition. In cases involving axial tension, ϕ is always 0.9 (UBC 1909.3.2.2).

Generation of Biaxial Interaction Surfaces

Technical Note 10 - 3

Column Design

Concrete Frame Design UBC97

Figure 2 Idealized Strain Distribution for Generation of Interaction Surfaces

Technical Note 10 - 4

Generation of Biaxial Interaction Surfaces

Concrete Frame Design UBC97

Column Design

Figure 3 Idealization of Stress and Strain Distribution in a Column Section

Calculate Column Capacity Ratio
The column capacity ratio is calculated for each loading combination at each output station of each column. The following steps are involved in calculating the capacity ratio of a particular column for a particular loading combination at a particular location: Determine the factored moments and forces from the analysis load cases and the specified load combination factors to give Pu, Mux, and Muy. Determine the moment magnification factors for the column moments. Apply the moment magnification factors to the factored moments. Determine whether the point, defined by the resulting axial load and biaxial moment set, lies within the interaction volume. The factored moments and corresponding magnification factors depend on the identification of the individual column as either “sway” or “non-sway.”

Calculate Column Capacity Ratio

Technical Note 10 - 5

Column Design

Concrete Frame Design UBC97

The following three sections describe in detail the algorithms associated with this process.

Determine Factored Moments and Forces
The factored loads for a particular load combination are obtained by applying the corresponding load factors to all the load cases, giving Pu, Mux, and Muy. The factored moments are further increased for non-sway columns, if required, to obtain minimum eccentricities of (0.6 + 0.03h) inches, where h is the dimension of the column in the corresponding direction (UBC 1910.12.3.2).

Determine Moment Magnification Factors
The moment magnification factors are calculated separately for sway (overall stability effect), δs, and for non-sway (individual column stability effect), δns. Also the moment magnification factors in the major and minor directions are in general different. The program assumes that it performs a P-delta analysis and, therefore, moment magnification factors for moments causing sidesway are taken as unity (UBC 1910.10.2). For the P-delta analysis, the load should correspond to a load combination of 0.75 (1.4 dead load + 1.7 live load)/ϕ if wind load governs, or (1.2 dead load + 0.50 live load)/ϕ if seismic load governs, where ϕ is the understrength factor for stability, which is taken as 0.75 (UBC 1910.12.3). See also White and Hajjar (1991). The moment obtained from analysis is separated into two components: the sway (Ms) and the non-sway (Ms) components. The non-sway components which are identified by “ns” subscripts are predominantly caused by gravity load. The sway components are identified by the “s” subscripts. The sway moments are predominantly caused by lateral loads, and are related to the cause of side-sway. For individual columns or column-members in a floor, the magnified moments about two axes at any station of a column can be obtained as M = Mns + δsMs. (UBC 1910.13.3) The factor δs is the moment magnification factor for moments causing side sway. The moment magnification factors for sway moments, δs, is taken as 1 because the component moments Ms and Mns are obtained from a “second order elastic (P-delta) analysis.”

Technical Note 10 - 6

Calculate Column Capacity Ratio

Concrete Frame Design UBC97

Column Design

The computed moments are further amplified for individual column stability effect (UBC 1910.12.3, 1910.13.5) by the nonsway moment magnification factor, δns, as follows: Mc = δnsM2 , where Mc is the factored moment to be used in design, and M2 is the larger factored and amplified end moment. The non-sway moment magnification factor, δns, associated with the major or minor direction of the column is given by (UBC 1910.12.3) δns = Cm ≥ 1.0, Pu 1− 0.75Pc π 2 EI (kl u )2 , where (UBC 1910.12.3) (UBC 1910.12.3)

Pc =

(UBC 1910.12.3)

k is conservatively taken as 1; however, the program allows the user to override this value. EI is associated with a particular column direction given by: EI = 0.4E c I g 1 + βd , (UBC 1910.12.3)

βd = maximum factored axial total load Cm = 0.6 + 0.4 Ma ≥ 0.4. Mb

maximum factored axial dead load

and

(UBC 1910.12.3) (UBC 1910.12.3.1)

Ma and Mb are the moments at the ends of the column, and Mb is numerically larger than Ma. Ma / Mb is positive for single curvature bending and negative for double curvature bending. The above expression of Cm is valid if there is no transverse load applied between the supports. If transverse load is present on the span, or the length is overwritten, Cm = 1. Cm can be overwritten by the user on an element-by-element basis.

Calculate Column Capacity Ratio

Technical Note 10 - 7

Column Design

Concrete Frame Design UBC97

The magnification factor, δns, must be a positive number and greater than 1. Therefore, Pu must be less than 0.75Pc. If Pu is found to be greater than or equal to 0.75Pc, a failure condition is declared. The above calculations use the unsupported length of the column. The two unsupported lengths are l22 and l33, corresponding to instability in the minor and major directions of the element, respectively. See Figure 4. These are the lengths between the support points of the element in the corresponding directions.

Figure 4 Axes of Bending and Unsupported Length
If the program assumptions are not satisfactory for a particular member, the user can explicitly specify values of δs and δns.

Determine Capacity Ratio
The program calculates a capacity ratio as a measure of the stress condition of the column. The capacity ratio is basically a factor that gives an indication

Technical Note 10 - 8

Calculate Column Capacity Ratio

Concrete Frame Design UBC97

Column Design

of the stress condition of the column with respect to the capacity of the column. Before entering the interaction diagram to check the column capacity, the moment magnification factors are applied to the factored loads to obtain Pu, Mux, and Muy. The point (Pu, Mux, Muy.) is then placed in the interaction space shown as point L in Figure 5. If the point lies within the interaction volume, the column capacity is adequate; however, if the point lies outside the interaction volume, the column is overstressed.

Figure 5 Geometric Representation of Column Capacity Ratios
This capacity ratio is achieved by plotting the point L and determining the location of point C. The point C is defined as the point where the line OL (if extended outwards) will intersect the failure surface. This point is determined by three-dimensional linear interpolation between the points that define the

Calculate Column Capacity Ratio

Technical Note 10 - 9

Column Design

Concrete Frame Design UBC97

failure surface. See Figure 5. The capacity ratio, CR, is given by the ratio OL . OC If OL = OC (or CR=1), the point lies on the interaction surface and the column is stressed to capacity. If OL < OC (or CR<1), the point lies within the interaction volume and the column capacity is adequate. If OL > OC (or CR>1), the point lies outside the interaction volume and the column is overstressed. The maximum of all the values of CR calculated from each load combination is reported for each check station of the column, along with the controlling Pu, Mux, and Muy set and associated load combination number.

Required Reinforcing Area
If the reinforcing area is not defined, the program computes the reinforcement that will give a column capacity ratio of one, calculated as described in the previous section entitled "Calculate Column Capacity Ratio."

Design Column Shear Reinforcement
The shear reinforcement is designed for each loading combination in the major and minor directions of the column. The following steps are involved in designing the shear reinforcing for a particular column for a particular load combination caused by shear forces in a particular direction: Determine the factored forces acting on the section, Pu and Vu. Note that Pu is needed for the calculation of Vc. Determine the shear force, Vc, that can be resisted by concrete alone. Calculate the reinforcement steel required to carry the balance. For Special and Intermediate moment resisting frames (Ductile frames), the shear design of the columns is also based on the probable and nominal moment capacities of the members, respectively, in addition to the factored

Technical Note 10 - 10

Required Reinforcing Area

Concrete Frame Design UBC97

Column Design

moments. Effects of the axial forces on the column moment capacities are included in the formulation. The following three sections describe in detail the algorithms associated with this process.

Determine Section Forces
In the design of the column shear reinforcement of an Ordinary moment resisting concrete frame, the forces for a particular load combination, namely, the column axial force, Pu, and the column shear force, Vu, in a particular direction are obtained by factoring the program analysis load cases with the corresponding load combination factors. In the shear design of Special moment resisting frames (i.e., seismic design) the column is checked for capacity-shear in addition to the requirement for the Ordinary moment resisting frames. The capacity-shear force in a column, Vp, in a particular direction is calculated from the probable moment capacities of the column associated with the factored axial force acting on the column. For each load combination, the factored axial load, Pu, is calculated. Then,
+ − the positive and negative moment capacities, Mu and Mu , of the column

in a particular direction under the influence of the axial force Pu is calculated using the uniaxial interaction diagram in the corresponding direction. The design shear force, Vu, is then given by (UBC 1921.4.5.1) Vu = Vp + VD+L (UBC 1921.4.5.1)

where, Vp is the capacity-shear force obtained by applying the calculated probable ultimate moment capacities at the two ends of the column acting in two opposite directions. Therefore, Vp is the maximum of VP1 and VP2 , where

VP1 = VP2 =

− + MI + M J , and L + − MI + M J , where L

Design Column Shear Reinforcement

Technical Note 10 - 11

Column Design

Concrete Frame Design UBC97

+ − M I , M I , = Positive and negative moment capacities at end I of the

column using a steel yield stress value of αfy and no ϕ factors (ϕ = 1.0),
+ − M J , M J , = Positive and negative moment capacities at end J of the

column using a steel yield stress value of αfy and no ϕ factors (ϕ = 1.0), and L = Clear span of column.

For Special moment resisting frames, α is taken as 1.25 (UBC 1921.0). VD+L is the contribution of shear force from the in-span distribution of gravity loads. For most of the columns, it is zero. For Intermediate moment resisting frames, the shear capacity of the column is also checked for the capacity-shear based on the nominal moment capacities at the ends and the factored gravity loads, in addition to the check required for Ordinary moment resisting frames. The design shear force is taken to be the minimum of that based on the nominal (ϕ = 1.0) moment capacity and factored shear force. The procedure for calculating nominal moment capacity is the same as that for computing the probable moment capacity for special moment resisting frames, except that α is taken equal to 1 rather than 1.25 (UBC 1921.0, 1921.8.3). The factored shear forces are based on the specified load factors, except the earthquake load factors are doubled (UBC 1921.8.3).

Determine Concrete Shear Capacity
Given the design force set Pu and Vu, the shear force carried by the concrete, Vc, is calculated as follows: If the column is subjected to axial compression, i.e., Pu is positive,  Pu Vc = 2 f c' 1 +  2,000 Ag  where, f c' ≤ 100 psi, and (UBC 1911.1.2)   Acv ,   (UBC 1911.3.1.2)

Technical Note 10 - 12

Design Column Shear Reinforcement

Concrete Frame Design UBC97

Column Design

Vc ≤ 3.5 f c'

 1 + Pu  500 Ag 

  Acv .  

(UBC 1911.3.2.2)

The term

Pu must have psi units. Acv is the effective shear area which is Ag

shown shaded in Figure 6. For circular columns, Acv is not taken to be greater than 0.8 times the gross area (UBC 1911.5.6.2).

Figure 6 Shear Stress Area, Acv

Design Column Shear Reinforcement

Technical Note 10 - 13

Column Design

Concrete Frame Design UBC97

If the column is subjected to axial tension, Pu is negative, (UBC 1911.3.2.3)  Pu Vc = 2 f c' 1 +  500 Ag    Acv ≥ 0   (UBC 1911.3.2.3)

For Special moment resisting concrete frame design, Vc is set to zero if the factored axial compressive force, Pu, including the earthquake effect is small (Pu < f c' Ag / 20) and if the shear force contribution from earthquake, VE, is more than half of the total factored maximum shear force over the length of the member Vu(VE ≥ 0.5Vu) (UBC 1921.4.5.2).

Determine Required Shear Reinforcement
Given Vu and Vc, the required shear reinforcement in the form of stirrups or ties within a spacing, s, is given for rectangular and circular columns by the following: Av = (Vu / ϕ − Vc )s , for rectangular columns f ys d 2 (Vu / ϕ − Vc )s , for circular columns f ys D' π (UBC 1911.5.6.1, 1911.5.6.2)

Av =

(UBC 1911.5.6.1, 1911.5.6.2)

Vu is limited by the following relationship. (Vu / ϕ-Vc) ≤ 8 f c' Acv (UBC 1911.5.6.8)

Otherwise redimensioning of the concrete section is required. Here ϕ, the strength reduction factor, is 0.85 for nonseismic design or for seismic design in Seismic Zones 0, 1, and 2 (UBC 1909.3.2.3) and is 0.60 for seismic design in Seismic Zones 3 and 4 (UBC 1909.3.4.1). The maximum of all the calculated values obtained from each load combination are reported for the major and minor directions of the column, along with the controlling shear force and associated load combination label. The column shear reinforcement requirements reported by the program are based purely on shear strength consideration. Any minimum stirrup requirements to satisfy spacing considerations or transverse reinforcement volumet-

Technical Note 10 - 14

Design Column Shear Reinforcement

Concrete Frame Design UBC97

Column Design

ric considerations must be investigated independently of the program by the user.

Reference
White. D. W., and J.F., Hajjar. 1991. Application of Second-Order Elastic Analysis in LRFD: Research in Practice. Engineering Journal. American Institute of Steel Construction, Inc. Vol. 28, No. 4.

Reference

Technical Note 10 - 15

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN UBC97

Technical Note 11

Beam Design
This Technical Note describes how this program completes beam design when the UBC97 code is selected. The program calculates and reports the required areas of steel for flexure and shear based on the beam moments, shears, load combination factors and other criteria described herein.

Overview
In the design of concrete beams, the program calculates and reports the required areas of steel for flexure and shear based upon the beam moments, shears, load combination factors, and other criteria described below. The reinforcement requirements are calculated at a user-defined number of check/design stations along the beam span. All beams are designed for major direction flexure and shear only. Effects caused by axial forces, minor direction bending, and torsion that may exist in the beams must be investigated independently by the user. The beam design procedure involves the following steps: Design beam flexural reinforcement Design beam shear reinforcement

Design Beam Flexural Reinforcement
The beam top and bottom flexural steel is designed at check/design stations along the beam span. The following steps are involved in designing the flexural reinforcement for the major moment for a particular beam for a particular section: Determine the maximum factored moments Determine the reinforcing steel

Overview

Technical Note 11 - 1

Beam Design

Concrete Frame Design UBC97

Determine Factored Moments
In the design of flexural reinforcement of Special, Intermediate, or Ordinary moment resisting concrete frame beams, the factored moments for each load combination at a particular beam section are obtained by factoring the corresponding moments for different load cases with the corresponding load factors.
+ The beam section is then designed for the maximum positive M u and maxi− mum negative M u factored moments obtained from all of the load combina-

tions. Negative beam moments produce top steel. In such cases, the beam is always designed as a rectangular section. Positive beam moments produce bottom steel. In such cases, the beam may be designed as a Rectangular- or a T-beam.

Determine Required Flexural Reinforcement
In the flexural reinforcement design process, the program calculates both the tension and compression reinforcement. Compression reinforcement is added when the applied design moment exceeds the maximum moment capacity of a singly reinforced section. The user has the option of avoiding the compression reinforcement by increasing the effective depth, the width, or the grade of concrete. The design procedure is based on the simplified rectangular stress block as shown in Figure 1 (UBC 1910.2). It is assumed that the compression carried by concrete is less than 0.75 times that which can be carried at the balanced condition (UBC 1910.3.3). When the applied moment exceeds the moment capacity at this designed balanced condition, the area of compression reinforcement is calculated assuming that the additional moment will be carried by compression and additional tension reinforcement. The design procedure used by the program for both rectangular and flanged sections (L- and T-beams) is summarized below. It is assumed that the design ultimate axial force does not exceed 0.1 f c' Ag (UBC 1910.3.3); hence, all the beams are designed for major direction flexure and shear only.

Technical Note 11 - 2

Design Beam Flexural Reinforcement

Concrete Frame Design UBC97

Beam Design

Figure 1 Design of a Rectangular Beam Section

Design for Rectangular Beam
In designing for a factored negative or positive moment, Mu (i.e., designing top or bottom steel), the depth of the compression block is given by a (see Figure 1), where, a=dd2 − 2 Mu 0.85f c' ϕb ,

where the value of ϕ is 0.90 (UBC 1909.3.2.1) in the above and the following equations. Also β1 and cb are calculated as follows:  f ' − 4,000  , β1 = 0.85 - 0.05  c  1,000    cb = εc E s 87,000 d. d = ε c E s + fy 87,000 + f y 0.65 ≤ β1 ≤ 0.85, (UBC 1910.2.7.3)

(UBC 1910.2.3, 1910.2.4)

Design Beam Flexural Reinforcement

Technical Note 11 - 3

Beam Design

Concrete Frame Design UBC97

The maximum allowed depth of the compression block is given by amax = 0.75β1cb. (UBC 1910.2.7.1, 1910.3.3)

If a ≤ amax, the area of tensile steel reinforcement is given by As = Mu a  ϕf y  d −  2  .

This steel is to be placed at the bottom if Mu is positive, or at the top if Mu is negative. If a > amax, compression reinforcement is required (UBC 1910.3.3) and is calculated as follows:
−

The compressive force developed in concrete alone is given by C = 0.85 f c' bamax, and (UBC 1910.2.7.1)

the moment resisted by concrete compression and tensile steel is a  Muc = C  d − max  2 
−

  ϕ.  

Therefore the moment resisted by compression steel and tensile steel is Mus = Mu - Muc.

−

So the required compression steel is given by
' As =

M us f s' (d − d' )ϕ

, where

 c − d'  f s' = 0.003Es   .  c 
−

(UBC 1910.2.4)

The required tensile steel for balancing the compression in concrete is

Technical Note 11 - 4

Design Beam Flexural Reinforcement

Concrete Frame Design UBC97

Beam Design

As1 =

Muc a   f y d − max  ϕ 2  

, and

the tensile steel for balancing the compression in steel is given by As2 = M us . f y (d − d' )ϕ

−

Therefore, the total tensile reinforcement, As = As1 + As2, and total com' ' pression reinforcement is As . As is to be placed at bottom and As is to

be placed at top if Mu is positive, and vice versa if Mu is negative.

Design for T-Beam
In designing for a factored negative moment, Mu (i.e., designing top steel), the calculation of the steel area is exactly the same as above, i.e., no T-Beam data is to be used. See Figure 2. If Mu > 0, the depth of the compression block is given by a = d - d2 − 2M u 0.85f c' ϕbf .

The maximum allowed depth of the compression block is given by amax = 0.75β1cb. (UBC 1910.2.7.1)

If a ≤ ds, the subsequent calculations for As are exactly the same as previously defined for the rectangular section design. However, in this case, the width of the compression flange is taken as the width of the beam for analysis. Compression reinforcement is required if a > amax. If a > ds, calculation for As is performed in two parts. The first part is for balancing the compressive force from the flange, Cf, and the second part is for balancing the compressive force from the web, Cw, as shown in Figure 2. Cf is given by Cf = 0.85 f c' (bf - bw) ds.

Design Beam Flexural Reinforcement

Technical Note 11 - 5

Beam Design

Concrete Frame Design UBC97

Figure 2 Design of a T-Beam Section
Therefore, As1 = given by d  Muf = Cf  d − s  2   ϕ .   Cf fy and the portion of Mu that is resisted by the flange is

Again, the value for ϕ is 0.90. Therefore, the balance of the moment, Mu to be carried by the web is given by Muw = Mu - Muf. The web is a rectangular section of dimensions bw and d, for which the design depth of the compression block is recalculated as a1 = d d2 − 2M uw 0.85f c' ϕbw .

If a1 ≤ amax, the area of tensile steel reinforcement is then given by

Technical Note 11 - 6

Design Beam Flexural Reinforcement

Concrete Frame Design UBC97

Beam Design

As2 =

M uw a   ϕf y  d − 1   2   

, and

As = As1 + As2. This steel is to be placed at the bottom of the T-beam. If a1 > amax, compression reinforcement is required (UBC 1910.3.3) and is calculated as follows:
−

The compressive force in web concrete alone is given by C = 0.85 f c' bamax. (UBC 1910.2.7.1)

−

Therefore the moment resisted by concrete web and tensile steel is a  Muc = C  d − max  2    ϕ, and  

the moment resisted by compression steel and tensile steel is Mus = Muw - Muc.
−

Therefore, the compression steel is computed as
' As =

M us f s' (d − d' )ϕ

, where

 c − d'  f s' = 0.003Es  .  c 
−

(UBC 1910.2.4)

The tensile steel for balancing compression in web concrete is As2 = M uc a  f y  d − max  2   ϕ   , and

the tensile steel for balancing compression in steel is

Design Beam Flexural Reinforcement

Technical Note 11 - 7

Beam Design

Concrete Frame Design UBC97

As3 =

Mus . f y (d − d')ϕ

−

The total tensile reinforcement, As = As1 + As2 + As3, and total compres' ' sion reinforcement is As . As is to be placed at bottom and As is to be

placed at top.

Minimum Tensile Reinforcement
The minimum flexural tensile steel provided in a rectangular section in an Ordinary moment resisting frame is given by the minimum of the two following limits: 3 f '  200   c As ≥ max  bw d and bw d  or fy  fy    As ≥ 4 As(required) 3 (UBC 1910.5.1)

(UBC 1910.5.3)

Special Consideration for Seismic Design
For Special moment resisting concrete frames (seismic design), the beam design satisfies the following additional conditions (see also Table 1 for comprehensive listing): The minimum longitudinal reinforcement shall be provided at both the top and bottom. Any of the top and bottom reinforcement shall not be less than As(min) (UBC 1921.3.2.1). 3 f '  200   c As(min) ≥ max  bw d and bw d  or fy  fy    As(min) ≥ 4 As(required). 3 (UBC 1910.5.1, 1921.3.2.1)

(UBC 1910.5.3, 1921.3.2.1)

The beam flexural steel is limited to a maximum given by As ≤ 0.25 bwd. (UBC 1921.3.2.1)

Technical Note 11 - 8

Design Beam Flexural Reinforcement

Concrete Frame Design UBC97

Beam Design

Table 1 Design Criteria Table
Type of Check/ Design Column Check (interaction) Column Design (interaction) Column Shears Ordinary Moment Resisting Frames (Seismic Zones 0&1) NLDa Combinations NLDa Combinations 1% < ρ < 8% Intermediate Moment Resisting Frames (Seismic Zone 2) NLDa Combinations Special Moment Resisting Frames (Seismic Zones 3 & 4) NLDa Combinations NLDa Combinations α = 1.0 1% < ρ < 6% NLDa Combinations and Column shear capacity ϕ = 1.0 and α = 1.25 NLDa Combinations ρ ≤ 0.025 ρ≥
3 f c' fy ,ρ ≥ 200 fy

NLDa Combinations 1% < ρ < 8% Modified NLDa Combinations (earthquake loads doubled) Column Capacity ϕ = 1.0 and α = 1.0

NLDa

Combinations

Beam Design Flexure

NLDa Combinations

NLDa Combinations

Beam Min. Moment Override Check

+ M uEND ≥

No Requirement

+ M uSPAN
− M uSPAN

1 − M uEND 3 1 + − ≥ max M u , M u 5

+ MuEND ≥

{

}

1 − MuEND 2

END

+ MuSPAN ≥ − MuSPAN

≥

1 + − max M u , M u 5

{

}

END

1 + − max Mu , Mu 4 1 − − ≥ max Mu , Mu 4

{ {

} }

END

END

Beam Design Shear Joint Design Beam/ Column Capacity Ratio

NLDa Combinations

Modified NLDa Combinations (earthquake loads doubled) Beam Capacity Shear (Vp) with α = 1.0 and ϕ = 1.0 plus VD+L No Requirement

NLDa Combinations Beam Capacity Shear (Vp) with α = 1.25 and ϕ = 1.0 plus VD+L Vc = 0 Checked for shear

No Requirement

No Requirement

No Requirement

Reported in output file

NLDa = Number of specified loading

Design Beam Flexural Reinforcement

Technical Note 11 - 9

Beam Design

Concrete Frame Design UBC97

At any end (support) of the beam, the beam positive moment capacity (i.e., associated with the bottom steel) would not be less than 1/2 of the beam negative moment capacity (i.e., associated with the top steel) at that end (UBC 1921.3.2.2). Neither the negative moment capacity nor the positive moment capacity at any of the sections within the beam would be less than 1/4 of the maximum of positive or negative moment capacities of any of the beam end (support) stations (UBC 1921.3.2.2). For Intermediate moment resisting concrete frames (i.e., seismic design), the beam design would satisfy the following conditions: At any support of the beam, the beam positive moment capacity would not be less than 1/3 of the beam negative moment capacity at that end (UBC 1921.8.4.1). Neither the negative moment capacity nor the positive moment capacity at any of the sections within the beam would be less than 1/5 of the maximum of positive or negative moment capacities of any of the beam end (support) stations (UBC 1921.8.4.1).

Design Beam Shear Reinforcement
The shear reinforcement is designed for each load combination at a userdefined number of stations along the beam span. The following steps are involved in designing the shear reinforcement for a particular beam for a particular load combination at a particular station resulting from the beam major shear: Determine the factored shear force, Vu. Determine the shear force, Vc, that can be resisted by the concrete. Determine the reinforcement steel required to carry the balance. For Special and Intermediate moment resisting frames (Ductile frames), the shear design of the beams is also based on the probable and nominal moment capacities of the members, respectively, in addition to the factored load design.

Technical Note 11 - 10

Design Beam Shear Reinforcement

Concrete Frame Design UBC97

Beam Design

The following three sections describe in detail the algorithms associated with this process.

Determine Shear Force and Moment
In the design of the beam shear reinforcement of an Ordinary moment resisting concrete frame, the shear forces and moments for a particular load combination at a particular beam section are obtained by factoring the associated shear forces and moments with the corresponding load combination factors. In the design of Special moment resisting concrete frames (i.e., seismic design), the shear capacity of the beam is also checked for the capacity-shear associated with the probable moment capacities at the ends and the factored gravity load. This check is performed in addition to the design check required for Ordinary moment resisting frames. The capacity-shear force, Vp, is calculated from the probable moment capacities of each end of the beam and the gravity shear forces. The procedure for calculating the design shear force in a beam from probable moment capacity is the same as that described for a column in section “Design Column Shear Reinforcement” in Concrete Frame Design UBC97 Technical Note 10 Column Design. See also Table 1 for details. The design shear force Vu is then given by (UBC 1921.3.4.1) Vu = Vp + VD+L (UBC 1921.3.4.1)

where Vp is the capacity shear force obtained by applying the calculated probable ultimate moment capacities at the two ends of the beams acting in opposite directions. Therefore, Vp is the maximum of VP1 and VP2 , where

VP1 = VP2 =
− MI

− + MI + M J , and L + − MI + M J , where L

= Moment capacity at end I, with top steel in tension, using a steel yield stress value of αfy and no ϕ factors (ϕ = 1.0),

Design Beam Shear Reinforcement

Technical Note 11 - 11

Beam Design

Concrete Frame Design UBC97

+ MJ

= Moment capacity at end J, with bottom steel in tension, using a steel yield stress value of αfy and no ϕ factors (ϕ = 1.0),

+ MI

= Moment capacity at end I, with bottom steel in tension, using a steel yield stress value of αfy and no ϕ factors (ϕ = 1.0),

− MJ

= Moment capacity at end J, with top steel in tension, using a
steel yield stress value of αfy and no ϕ factors (ϕ = 1.0), and

L

= Clear span of beam.

For Special moment resisting frames, α is taken as 1.25 (UBC 1921.0). VD+L is the contribution of shear force from the in-span distribution of gravity loads. For Intermediate moment resisting frames, the shear capacity of the beam is also checked for the capacity shear based on the nominal moment capacities at the ends and the factored gravity loads, in addition to the check required for Ordinary moment resisting frames. The design shear force in beams is taken to be the minimum of that based on the nominal moment capacity and factored shear force. The procedure for calculating nominal (ϕ = 1.0) moment capacity is the same as that for computing the probable moment capacity for Special moment resisting frames, except that α is taken equal to 1 rather than 1.25 (UBC 1921.0, 1921.8.3). The factored shear forces are based on the specified load factors, except the earthquake load factors are doubled (UBC 1921.8.3). The computation of the design shear force in a beam of an Intermediate moment resisting frame is also the same as that for columns, which is described in Concrete Frame Design UBC97 Technical Note 10 Column Design. Also see Table 1 for details.

Determine Concrete Shear Capacity
The allowable concrete shear capacity is given by Vc = 2 f c' bwd. (UBC 1911.3.1.1)

For Special moment resisting frame concrete design, Vc is set to zero if both the factored axial compressive force, including the earthquake effect Pu, is less than f c' Ag/20 and the shear force contribution from earthquake VE is

Technical Note 11 - 12

Design Beam Shear Reinforcement

Concrete Frame Design UBC97

Beam Design

more than half of the total maximum shear force over the length of the member Vu (i.e., VE ≥ 0.5Vu) (UBC 1921.3.4.2).

Determine Required Shear Reinforcement
Given Vu and Vc, the required shear reinforcement in area/unit length is calculated as Av = (Vu / ϕ − Vc )s . f ys d (UBC 1911.5.6.1, 1911.5.6.2)

The shear force resisted by steel is limited by (Vu/ϕ - Vc) ≤ 8 f c' bd. (UBC 1911.5.6.8)

Otherwise, redimensioning of the concrete section is required. Here ϕ, the strength reduction factor, is 0.85 for nonseismic design or for seismic design in Seismic Zones 0, 1, and 2 (UBC 1909.3.2.3) and is 0.60 for seismic design in Seismic Zones 3 and 4 (UBC 1909.3.4.1). The maximum of all the calculated Av values, obtained from each load combination, is reported along with the controlling shear force and associated load combination number. The beam shear reinforcement requirements displayed by the program are based purely on shear strength considerations. Any minimum stirrup requirements to satisfy spacing and volumetric considerations must be investigated independently of the program by the user.

Design Beam Shear Reinforcement

Technical Note 11 - 13

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN UBC97

Technical Note 12 Joint Design
This Technical Note explains how the program performs a rational analysis of the beam-column panel zone to determine the shear forces that are generated in a joint. The program then checks this against design shear strength.

Overview
To ensure that the beam-column joint of special moment resisting frames possesses adequate shear strength, the program performs a rational analysis of the beam-column panel zone to determine the shear forces that are generated in the joint. The program then checks this against design shear strength. Only joints having a column below the joint are designed. The material properties of the joint are assumed to be the same as those of the column below the joint. The joint analysis is completed in the major and the minor directions of the column. The joint design procedure involves the following steps: • • • Determine the panel zone design shear force,Vuh Determine the effective area of the joint Check panel zone shear stress

The algorithms associated with these three steps are described in detail in the following three sections.

Determine the Panel Zone Shear Force
Figure 1 illustrates the free body stress condition of a typical beam-column intersection for a column direction, major or minor.

Overview

Technical Note 12 - 1

Joint Design

Concrete Frame Design UBC97

Figure1 Beam-Column Joint Analysis

Technical Note 12 - 2

Determine the Panel Zone Shear Force

Concrete Frame Design UBC97

Joint Design

The force Vuh is the horizontal panel zone shear force that is to be calculated. The forces that act on the joint are Pu, Vu, MuL and MuR. The forces Pu and Vu are axial force and shear force, respectively, from the column framing into the top of the joint. The moments MuL and MuR are obtained from the beams framing into the joint. The program calculates the joint shear force Vuh by resolving the moments into C and T forces. Noting that TL = CL and TR = CR, Vuh = TL + TR - Vu The location of C or T forces is determined by the direction of the moment. The magnitude of C or T forces is conservatively determined using basic principles of ultimate strength theory, ignoring compression reinforcement as follows. The program first calculates the maximum compression, Cmax, and the maximum moment, Mmax, that can be carried by the beam. C max = 0.85f c' bd Mmax = C max d 2

Then the program conservatively determines C and T forces as follows:

 abs( M )   C = T = C max 1 − 1 −  M max   
The program resolves the moments and the C and T forces from beams that frame into the joint in a direction that is not parallel to the major or minor directions of the column along the direction that is being investigated, thereby contributing force components to the analysis. Also, the program calculates the C and T for the positive and negative moments, considering the fact that the concrete cover may be different for the direction of moment. In the design of special moment resisting concrete frames, the evaluation of the design shear force is based on the moment capacities (with reinforcing steel overstrength factor, α, and no ϕ factors) of the beams framing into the joint (UBC 1921.5.1.1). The C and T forces are based on these moment capacities. The program calculates the column shear force Vu from the beam moment capacities, as follows:

Determine the Panel Zone Shear Force

Technical Note 12 - 3

Joint Design

Concrete Frame Design UBC97

Vu =

Mu + Mu H

L

R

See Figure 2. It should be noted that the points of inflection shown on Figure 2 are taken as midway between actual lateral support points for the columns. If there is no column at the top of the joint, the shear force from the top of the column is taken as zero.

Figure 2 Column Shear Force Vu

Technical Note 12 - 4

Determine the Panel Zone Shear Force

Concrete Frame Design UBC97

Joint Design

The effects of load reversals, as illustrated in Case 1 and Case 2 of Figure 1, are investigated and the design is based on the maximum of the joint shears obtained from the two cases.

Determine the Effective Area of Joint
The joint area that resists the shear forces is assumed always to be rectangular in plan view. The dimensions of the rectangle correspond to the major and minor dimensions of the column below the joint, except if the beam framing into the joint is very narrow. The effective width of the joint area to be used in the calculation is limited to the width of the beam plus the depth of the column. The area of the joint is assumed not to exceed the area of the column below. The joint area for joint shear along the major and minor directions is calculated separately (ACI R21.5.3). It should be noted that if the beam frames into the joint eccentrically, the above assumptions may be unconservative and the user should investigate the acceptability of the particular joint.

Check Panel Zone Shear Stress
The panel zone shear stress is evaluated by dividing the shear force Vuh by the effective area of the joint and comparing it with the following design shear strengths (UBC 1921.5.3):

v =

{

20ϕ 15ϕ 12ϕ

f 'c f 'c f 'c

for joints confined on all four sides for joints confined on three faces or on two opposite faces for all other joints

where ϕ = 0.85 (by default).

(UBC 1909.3.2.3,1909.3.4.1)

A beam that frames into a face of a column at the joint is considered in this program to provide confinement to the joint if at least three-quarters of the face of the joint is covered by the framing member (UBC 1921.5.3.1).

Determine the Effective Area of Joint

Technical Note 12 - 5

Joint Design

Concrete Frame Design UBC97

For light-weight aggregate concrete, the design shear strength of the joint is reduced in the program to at least three-quarters of that of the normal weight concrete by replacing the minf cs, factor f ' c ,3 / 4 f c'      f c' with (UBC 1921.5.3.2)

For joint design, the program reports the joint shear, the joint shear stress, the allowable joint shear stress and a capacity ratio.

Beam/Column Flexural Capacity Ratios
At a particular joint for a particular column direction, major or minor, the program will calculate the ratio of the sum of the beam moment capacities to the sum of the column moment capacities. For Special Moment-Resisting Frames, the following UBC provision needs to be satisfied (UBC 1921.4.2.2). ∑Me ≥ 6 ∑Mg 5 (UBC 1921.4.2.2)

The capacities are calculated with no reinforcing overstrength factor, α, and including ϕ factors. The beam capacities are calculated for reversed situations (Cases 1 and 2) as illustrated in Figure 1 and the maximum summation obtained is used. The moment capacities of beams that frame into the joint in a direction that is not parallel to the major or minor direction of the column are resolved along the direction that is being investigated and the resolved components are added to the summation. The column capacity summation includes the column above and the column below the joint. For each load combination, the axial force, Pu, in each of the columns is calculated from the program analysis load combinations. For each load combination, the moment capacity of each column under the influence of the corresponding axial load Pu is then determined separately for the major and minor directions of the column, using the uniaxial column interaction diagram, see Figure 3. The moment capacities of the two columns are added to give the capacity summation for the corresponding load combination. The maximum capacity summations obtained from all of the load combinations is used for the beam/column capacity ratio.

Technical Note 12 - 6

Beam/Column Flexural Capacity Ratios

Concrete Frame Design UBC97

Joint Design

The beam/column flexural capacity ratios are only reported for Special Moment-Resisting Frames involving seismic design load combinations. If this ratio is greater than 5/6, a warning message is printed in the output file.

Figure 3 Moment Capacity Mu at a Given Axial Load Pu

Beam/Column Flexural Capacity Ratios

Technical Note 12 - 7

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN UBC97

Technical Note 13

Input Data
This Technical Note describes the concrete frame design input data for UBC97. The input can be printed to a printer or to a text file when you click the File menu > Print Tables > Concrete Frame Design command. A printout of the input data provides the user with the opportunity to carefully review the parameters that have been input into the program and upon which program design is based. Further information about using the Print Design Tables form is presented at the end of this Technical Note.

Input Data
The program provides the printout of the input data in a series of tables. The column headings for input data and a description of what is included in the columns of the tables are provided in Table 1 of this Technical Note.

Table 1 Concrete Frame Design Input Data
COLUMN HEADING Combo Type Case Factor DESCRIPTION Design load combination. See Technical Note 8. Load type: dead, live, superimposed dead, earthquake, wind, snow, reduced live load, other. Name of load case. Load combination scale factor. Bending strength reduction factor. Tensile strength reduction factor. Compressive strength reduction factor for tied columns. Compressive strength reduction factor for reinforced columns. Shear strength reduction factor.

Load Combination Multipliers

Code Preferences
Phi_bending Phi_tension Phi_compression (Tied) Phi_compression (Spiral) Phi_shear

Input Data

Technical Note 13 - 1

Input Data

Concrete Frame Design UBC97

Table 1 Concrete Frame Design Input Data
COLUMN HEADING DESCRIPTION Concrete, steel, other. Isotropic or orthotropic.

Material Property Data
Material Name Material Type Design Type Modulus of Elasticity Poisson's Ratio Thermal Coeff Shear Modulus Coefficient of thermal expansion.

Material Property Mass and Weight
Material Name Mass Per Unit Vol Weight Per Unit Vol Material Name Lightweight Concrete Concrete FC Rebar FY Rebar FYS Lightwt Reduc Fact Concrete compressive strength. Bending reinforcing steel yield strength. Shear reinforcing steel yield strength. Shear strength reduction factor for light weight concrete; default = 1.0. Label applied to section. Material label. Concrete, steel, other. Used to calculate self-mass of structure. Used to calculate self-weight of structure. Concrete, steel, other.

Material Design Data for Concrete Materials

Concrete Column Property Data
Section Label Mat Label Column Depth Column Width Rebar Pattern Concrete Cover Bar Area Layout of main flexural reinforcing steel. Minimum clear concrete cover. Area of individual reinforcing bar to be used.

Technical Note 13 - 2

Table 1 Concrete Frame Design Input Data

Concrete Frame Design UBC97

Input Data

Table 1 Concrete Frame Design Input Data
COLUMN HEADING Story ID Column Line Section ID Framing Type RLLF Factor L_Ratio Major L_Ratio Minor K Major K Minor Story ID Bay ID Section ID Framing type RLLF Factor L_Ratio Major L_Ratio Minor Unbraced length about major axis. Unbraced length about minor axis. Unbraced length about major axis. Unbraced length about minor axis. Effective length factor; default = 1.0. Effective length factor; default = 1.0. Story level at which beam occurs. Grid lines locating beam. Section number assigned to beam. Lateral or gravity. DESCRIPTION Column assigned to story level at top of column. Grid line. Name of section assigned to column. Lateral or gravity.

Concrete Column Design Element Information

Concrete Beam Design Element Information

Using the Print Design Tables Form
To print steel frame design input data directly to a printer, use the File menu > Print Tables > Concrete Frame Design command and click the check box on the Print Design Tables form. Click the OK button to send the print to your printer. Click the Cancel button rather than the OK button to cancel the print. Use the File menu > Print Setup command and the Setup>> button to change printers, if necessary. To print steel frame design input data to a file, click the Print to File check box on the Print Design Tables form. Click the Filename>> button to change the

Using the Print Design Tables Form

Technical Note 13 - 3

Input Data

Concrete Frame Design UBC97

path or filename. Use the appropriate file extension for the desired format (e.g., .txt, .xls, .doc). Click the OK buttons on the Open File for Printing Tables form and the Print Design Tables form to complete the request. Note: The File menu > Display Input/Output Text Files command is useful for displaying output that is printed to a text file. The Append check box allows you to add data to an existing file. The path and filename of the current file is displayed in the box near the bottom of the Print Design Tables form. Data will be added to this file. Or use the Filename>> button to locate another file, and when the Open File for Printing Tables caution box appears, click Yes to replace the existing file. If you select a specific frame element(s) before using the File menu > Print Tables > Concrete Frame Design command, the Selection Only check box will be checked. The print will be for the selected beam(s) only.

Technical Note 13 - 4

Using the Print Design Tables Form

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN UBC97

Technical Note 14

Output Details
This Technical Note describes the concrete frame design output for UBC97 that can be printed to a printer or to a text file. The design output is printed when you click the File menu > Print Tables > Concrete Frame Design command and select Output Summary of the Print Design Tables dialog box. Further information about using the Print Design Tables dialog box is presented at the end of this Technical Note. The program provides the output data in a series of tables. The column headings for output data and a description of what is included in the columns of the tables are provided in Table 1 of this Technical Note.

Table 1 Concrete Column Design Output
COLUMN HEADING Story ID Column Line Section ID Station ID DESCRIPTION Column assigned to story level at top of column. Grid lines. Name of section assigned to column.

Biaxial P-M Interaction and Shear Design of Column-Type Elements

Required Reinforcing
Longitudinal Combo Shear22 Combo Shear33 Area of longitudinal reinforcing required. Load combination for which the reinforcing is designed. Shear reinforcing required. Load combination for which the reinforcing is designed. Shear reinforcing required.

Table 1 Concrete Column Design Output

Technical Note 14 - 1

Output Details

Concrete Frame Design UBC97

Table 1 Concrete Column Design Output
COLUMN HEADING Combo DESCRIPTION Load combination for which the reinforcing is designed.

Table 2 Concrete Column Joint Output
COLUMN HEADING DESCRIPTION Beam to Column Capacity Ratios and Joint Shear Capacity Check Story ID Column Line Section ID Story level at which joint occurs. Grid line. Assigned section name.

Beam-Column Capacity Ratios Major Combo Ratio of beam moment capacity to column capacity. Load combination upon which the ratio of beam moment capacity to column capacity is based. Ratio of beam moment capacity to column capacity. Load combination upon which the ratio of beam moment capacity to column capacity is based.

Minor Combo

Joint Shear Capacity Ratios Major Combo Ratio of factored load versus allowed capacity. Load combination upon which the ratio of factored load versus allowed capacity is based. Ratio of factored load versus allowed capacity. Load combination upon which the ratio of factored load versus allowed capacity is based.

Minor Combo

Technical Note 14 - 2

Table 2 Concrete Column Joint Output

Concrete Frame Design UBC97

Output Details

Using the Print Design Tables Form
To print concrete frame design input data directly to a printer, use the File menu > Print Tables > Concrete Frame Design command and click the check box on the Print Design Tables dialog box. Click the OK button to send the print to your printer. Click the Cancel button rather than the OK button to cancel the print. Use the File menu > Print Setup command and the Setup>> button to change printers, if necessary. To print concrete frame design input data to a file, click the Print to File check box on the Print Design Tables dialog box. Click the Filename>> button to change the path or filename. Use the appropriate file extension for the desired format (e.g., .txt, .xls, .doc). Click the OK buttons on the Open File for Printing Tables dialog box and the Print Design Tables dialog box to complete the request. Note: The File menu > Display Input/Output Text Files command is useful for displaying output that is printed to a text file. The Append check box allows you to add data to an existing file. The path and filename of the current file is displayed in the box near the bottom of the Print Design Tables dialog box. Data will be added to this file. Or use the Filename>> button to locate another file, and when the Open File for Printing Tables caution box appears, click Yes to replace the existing file. If you select a specific frame element(s) before using the File menu > Print Tables > Concrete Frame Design command, the Selection Only check box will be checked. The print will be for the selected beam(s) only.

Using the Print Design Tables Form

Technical Note 14 - 3

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN ACI-318-99

Technical Note 15

General and Notation Introduction to the ACI318-99 Series of Technical Notes
The ACI-318-99 Concrete Frame Design series of Technical Notes describes in detail the various aspects of the concrete design procedure that is used by this program when the user selects the ACI-318-99 Design Code (ACI 1999). The various notations used in this series are listed herein. The design is based on user-specified loading combinations. The program provides a set of default load combinations that should satisfy requirements for the design of most building type structures. See Concrete Frame Design ACI-318-99 Technical Note 18 Design Load Combination for more information. The program provides options to design or check Earthquake resisting frames; Ordinary, Earthquake resisting frames; Intermediate (moderate seismic risk areas), and Earthquake resisting frames; Special (high seismic risk areas) moment resisting frames as required for seismic design provisions. The details of the design criteria used for the different framing systems are described in Concrete Frame Design ACI-318-99 Technical Note 19 Strength Reduction Factors, Concrete Frame Design ACI-318-99 Technical Note 20 Column Design, Concrete Frame Design ACI-318-99 Technical Note 21 Beam Design, and Concrete Frame Design ACI-318-99 Technical Note 22 Joint Design. The program uses preferences and overwrites, which are described in Concrete Frame Design ACI-318-99 Technical Note 16 Preferences and Concrete Frame Design ACI-318-99 Technical Note 17 Overwrites. It also provides input and output data summaries, which are described in Concrete Frame Design ACI-318-99 Technical Note 23 Input Data and Concrete Frame Design ACI-318-99 Technical Note 24 Output Details. English as well as SI and MKS metric units can be used for input. But the code is based on Inch-Pound-Second units. For simplicity, all equations and descriptions presented in this chapter correspond to Inch-Pound-Second units unless otherwise noted.

Introduction to the ACI318-99 Series of Technical Notes

Technical Note 15 - 1

General and Notation

Concrete Frame Design ACI-318-99

Notation
Acv Ag As
' As

Area of concrete used to determine shear stress, sq-in Gross area of concrete, sq-in Area of tension reinforcement, sq-in Area of compression reinforcement, sq-in Area of steel required for tension reinforcement, sq-in Total area of column longitudinal reinforcement, sq-in Area of shear reinforcement, sq-in Coefficient, dependent upon column curvature, used to calculate moment magnification factor Modulus of elasticity of concrete, psi Modulus of elasticity of reinforcement, assumed as 29,000,000 psi (ACI 8.5.2) Moment of inertia of gross concrete section about centroidal axis, neglecting reinforcement, in4 Moment of inertia of reinforcement about centroidal axis of member cross section, in4 Clear unsupported length, in Smaller factored end moment in a column, lb-in Larger factored end moment in a column, lb-in Factored moment to be used in design, lb-in Nonsway component of factored end moment, lb-in Sway component of factored end moment, lb-in

As(required) Ast Av Cm

Ec Es

Ig

Ise

L M1 M2 Mc Mns Ms

Technical Note 15 - 2

Notation

Concrete Frame Design ACI-318-99

General and Notation

Mu Mux Muy Pb Pc Pmax P0 Pu Vc VE VD+L Vu Vp a ab b bf bw c cb d d'

Factored moment at section, lb-in Factored moment at section about X-axis, lb-in Factored moment at section about Y-axis, lb-in Axial load capacity at balanced strain conditions, lb Critical buckling strength of column, lb Maximum axial load strength allowed, lb Axial load capacity at zero eccentricity, lb Factored axial load at section, lb Shear resisted by concrete, lb Shear force caused by earthquake loads, lb Shear force from span loading, lb Factored shear force at a section, lb Shear force computed from probable moment capacity, lb Depth of compression block, in Depth of compression block at balanced condition, in Width of member, in Effective width of flange (T-Beam section), in Width of web (T-Beam section), in Depth to neutral axis, in Depth to neutral axis at balanced conditions, in Distance from compression face to tension reinforcement, in Concrete cover to center of reinforcing, in

Notation

Technical Note 15 - 3

General and Notation

Concrete Frame Design ACI-318-99

ds f c' fy

Thickness of slab (T-Beam section), in Specified compressive strength of concrete, psi Specified yield strength of flexural reinforcement, psi fy ≤ 80,000 psi (ACI 9.4) Specified yield strength of shear reinforcement, psi Dimension of column, in Effective length factor Radius of gyration of column section, in Reinforcing steel overstrength factor Absolute value of ratio of maximum factored axial dead load to maximum factored axial total load Absolute value of ratio or maximum factored axial dead load to maximum factored axial total load Moment magnification factor for sway moments Moment magnification factor for nonsway moments Strain in concrete Strain in reinforcing steel Strength reduction factor

fys h k r α β1

βd

δs δns εc εs ϕ

Technical Note 15 - 4

Notation

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN ACI318-99

Technical Note 16 Preferences
This Technical Note describes the items in the Preferences form.

General
The concrete frame design preferences in this program are basic assignments that apply to all concrete frame elements. Use the Options menu > Preferences > Concrete Frame Design command to access the Preferences form where you can view and revise the concrete frame design preferences. Default values are provided for all concrete frame design preference items. Thus, it is not required that you specify or change any of the preferences. You should, however, at least review the default values for the preference items to make sure they are acceptable to you.

Using the Preferences Form
To view preferences, select the Options menu > Preferences > Concrete Frame Design. The Preferences form will display. The preference options are displayed in a two-column spreadsheet. The left column of the spreadsheet displays the preference item name. The right column of the spreadsheet displays the preference item value. To change a preference item, left click the desired preference item in either the left or right column of the spreadsheet. This activates a drop-down box or highlights the current preference value. If the drop-down box appears, select a new value. If the cell is highlighted, type in the desired value. The preference value will update accordingly. You cannot overwrite values in the dropdown boxes. When you have finished making changes to the composite beam preferences, click the OK button to close the form. You must click the OK button for the changes to be accepted by the program. If you click the Cancel button to exit

General

Technical Note 16 - 1

Preferences

Concrete Frame Design ACI318-99

the form, any changes made to the preferences are ignored and the form is closed.

Preferences
For purposes of explanation in this Technical Note, the preference items are presented in Table. The column headings in the table are described as follows: Item: The name of the preference item as it appears in the cells at the left side of the Preferences form. Possible Values: The possible values that the associated preference item can have. Default Value: The built-in default value that the program assumes for the associated preference item. Description: A description of the associated preference item.

Table 1: Concrete Frame Preferences
Item Design Code Possible Values Any code in the program >0 >0 >0 >0 ≥4.0 Default Value ACI 318-99 Description Design code used for design of concrete frame elements. Unitless strength reduction factor per ACI 9.3. Unitless strength reduction factor per ACI 9.3. Unitless strength reduction factor per ACI 9.3. Unitless strength reduction factor per ACI 9.3. Number of equally spaced interaction curves used to create a full 360-degree interaction surface (this item should be a multiple of four). We recommend that you use 24 for this item.

Phi Bending Tension Phi Compression Tied Phi Compression Spiral Phi Shear Number Interaction Curves

0.9 0.7 0.75 0.85 24

Technical Note 16 - 2

Preferences

Concrete Frame Design ACI318-99

Preferences

Table 1: Concrete Frame Preferences
Item Possible Values Default Value 11 Description Number of points used for defining a single curve in a concrete frame interaction surface (this item should be odd). Toggle for design load combinations that include a time history designed for the envelope of the time history, or designed step-by-step for the entire time history. If a single design load combination has more than one time history case in it, that design load combination is designed for the envelopes of the time histories, regardless of what is specified here.

Number Inter- Any odd value action Points ≥4.0 Time History Design Envelopes or Step-by-Step

Envelopes

Preferences

Technical Note 16 - 3

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN ACI318-99

Technical Note 17

Overwrites General
The concrete frame design overwrites are basic assignments that apply only to those elements to which they are assigned. This Technical Note describes concrete frame design overwrites for ACI318-99. To access the overwrites, select an element and click the Design menu > Concrete Frame Design > View/Revise Overwrites command. Default values are provided for all overwrite items. Thus, you do not need to specify or change any of the overwrites. However, at least review the default values for the overwrite items to make sure they are acceptable. When changes are made to overwrite items, the program applies the changes only to the elements to which they are specifically assigned; that is, to the elements that are selected when the overwrites are changed.

Overwrites
For explanation purposes in this Technical Note, the overwrites are presented in Table 1. The column headings in the table are described as follows. Item: The name of the overwrite item as it appears in the program. To save space in the formes, these names are generally short. Possible Values: The possible values that the associated overwrite item can have. Default Value: The default value that the program assumes for the associated overwrite item. Description: A description of the associated overwrite item. An explanation of how to change an overwrite is provided at the end of this Technical Note.

Overwrites

Technical Note 17 - 1

Overwrites

Concrete Frame Design ACI318-99

Table 1 Concrete Frame Design Overwrites
Item Element Section Sway Special, Sway Special Frame type per moment frame definition given in ACI 21.1. Sway Intermediate, Sway Ordinary NonSway >0 ≤1.0 >0 ≤1.0 >0 ≤1.0 >0 ≤1.0 >0 ≤1.0 >0 ≤1.0 >0 ≤1.0 >0 ≤1.0 >0 ≤1.0 1 1 1 1 1 See ACI 10.12, 10.13 and Figure R10.12.1. See ACI 10.12, 10.13 and Figure R10.12.1. Factor relating actual moment diagram to an equivalent uniform moment diagram. See ACI 10.12.3. Factor relating actual moment diagram to an equivalent uniform moment diagram. See ACI 10.12.3. See ACI 10.12. 1.0 1.0 1 1. Used to reduce the live load contribution to the factored loading. Possible Values Default Value Description

Element Type

Live Load Reduction Factor Horizontal Earthquake Factor Unbraced Length Ratio (Major) Unbraced Length Ratio (Minor) Effective Length Factor (K Major) Effective Length Factor (K Minor) Moment Coefficient (Cm Major) Moment Coefficient (Cm Minor) NonSway Moment Factor (Dns Major)

Technical Note 17 - 2

Overwrites

Concrete Frame Design ACI318-99

Overwrites

Table 1 Concrete Frame Design Overwrites
Item NonSway Moment Factor (Dns Minor) Sway Moment Factor (Ds Major) Sway Moment Factor (Ds Minor) Possible Values Default Value 1 Description See ACI 10.13.

1

See ACI 10.13.

1

See ACI 10.13.

Making Changes in the Overwrites Form
To access the concrete frame overwrites, select an element and click the Design menu > Concrete Frame Design > View/Revise Overwrites command. The overwrites are displayed in the form with a column of check boxes and a two-column spreadsheet. The left column of the spreadsheet contains the name of the overwrite item. The right column of the spreadsheet contains the overwrites values. Initially, the check boxes in the Concrete Frame Design Overwrites form are all unchecked and all of the cells in the spreadsheet have a gray background to indicate that they are inactive and the items in the cells cannot be changed. The names of the overwrite items are displayed in the first column of the spreadsheet. The values of the overwrite items are visible in the second column of the spreadsheet if only one element was selected before the overwrites form was accessed. If multiple elements were selected, no values show for the overwrite items in the second column of the spreadsheet. After selecting one or multiple elements, check the box to the left of an overwrite item to change it. Then left click in either column of the spreadsheet to activate a drop-down box or highlight the contents in the cell in the right column of the spreadsheet. If the drop-down box appears, select a value from

Overwrites

Technical Note 17 - 3

Overwrites

Concrete Frame Design ACI318-99

the box. If the cell contents is highlighted, type in the desired value. The overwrite will reflect the change. You cannot change the values of the dropdown boxes. When changes to the overwrites have been completed, click the OK button to close the form. The program then changes all of the overwrite items whose associated check boxes are checked for the selected members. You must click the OK button for the changes to be accepted by the program. If you click the Cancel button to exit the form, any changes made to the overwrites are ignored and the form is closed.

Resetting Concrete Frame Overwrites to Default Values
Use the Design menu > Concrete Frame Design > Reset All Overwrites command to reset all of the steel frame overwrites. All current design results will be deleted when this command is executed. Important note about resetting overwrites: The program defaults for the overwrite items are built into the program. The concrete frame overwrite values that were in a .edb file that you used to initialize your model may be different from the built-in program default values. When you reset overwrites, the program resets the overwrite values to its built-in values, not to the values that were in the .edb file used to initialize the model.

Technical Note 17 - 4

Overwrites

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN ACI-318-99

Technical Note 18

Design Load Combinations
The design load combinations are the various combinations of the prescribed load cases for which the structure needs to be checked. For the ACI 318-99 code, if a structure is subjected to dead load (DL) and live load (LL) only, the stress check may need only one load combination, namely 1.4 DL + 1.7 LL (ACI 9.2.1). However, in addition to the dead and live loads, if the structure is subjected to wind (WL) and earthquake (EL) loads and considering that wind and earthquake forces are reversible, the following load combinations should be considered (ACI 9.2). 1.4 DL 1.4 DL + 1.7 LL 0.9 DL ± 1.3 WL 0.75 (1.4 DL + 1.7 LL ± 1.7 WL) 0.9 DL ± 1.3 * 1.1 EL 0.75 (1.4 DL + 1.7 LL ± 1.7 * 1.1 EL) (ACI 9.2.1)

(ACI 9.2.2)

(ACI 9.2.3)

These are also the default design load combinations in the program whenever the ACI 318-99 code is used. The user is warned that the above load combinations involving seismic loads consider service-level seismic forces. Different load factors may apply with strength-level seismic forces (ACI R9.2.3). Live load reduction factors can be applied to the member forces of the live load condition on an element-by-element basis to reduce the contribution of the live load to the factored loading. See Concrete Frame Design ACI 318-99 Technical Note 17 Overwrites for more information.

Design Load Combinations

Technical Note 18 - 1

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN ACI-318-99

Technical Note 19

Strength Reduction Factors
The strength reduction factors, ϕ, are applied on the nominal strength to obtain the design strength provided by a member. The ϕ factors for flexure, axial force, shear, and torsion are as follows: ϕ ϕ ϕ ϕ = 0.90 for flexure = 0.90 for axial tension = 0.90 for axial tension and flexure (ACI 9.3.2.1) (ACI 9.3.2.2) (ACI 9.3.2.2)

= 0.75 for axial compression, and axial compression and flexure (spirally reinforced column) (ACI 9.3.2.2) = 0.70 for axial compression, and axial compression and flexure (tied column) (ACI 9.3.2.2) = 0.85 for shear and torsion (ACI 9.3.2.3)

ϕ

ϕ

Strength Reduction Factors

Technical Note 19 - 1

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN ACI-318-99

Technical Note 20

Column Design
This Technical Note describes how the program checks column capacity or designs reinforced concrete columns when the ACI-318-99 code is selected.

Overview
The program can be used to check column capacity or to design columns. If you define the geometry of the reinforcing bar configuration of each concrete column section, the program will check the column capacity. Alternatively, the program can calculate the amount of reinforcing required to design the column. The design procedure for the reinforced concrete columns of the structure involves the following steps: Generate axial force/biaxial moment interaction surfaces for all of the different concrete section types of the model. A typical biaxial interaction surface is shown in Figure 1. When the steel is undefined, the program generates the interaction surfaces for the range of allowable reinforcement  1 to 8 percent for Ordinary and Intermediate moment resisting frames (ACI 10.9.1) and 1 to 6 percent for Special moment resisting frames (ACI 21.4.3.1). Calculate the capacity ratio or the required reinforcing area for the factored axial force and biaxial (or uniaxial) bending moments obtained from each loading combination at each station of the column. The target capacity ratio is taken as one when calculating the required reinforcing area. Design the column shear reinforcement. The following four sections describe in detail the algorithms associated with this process.

Overview

Technical Note 20 - 1

Column Design

Concrete Frame Design ACI-318-99

Figure 1 A Typical Column Interaction Surface

Generation of Biaxial Interaction Surfaces
The column capacity interaction volume is numerically described by a series of discrete points that are generated on the three-dimensional interaction failure surface. In addition to axial compression and biaxial bending, the formulation allows for axial tension and biaxial bending considerations. A typical interaction diagram is shown in Figure 1. The coordinates of these points are determined by rotating a plane of linear strain in three dimensions on the section of the column. See Figure 2. The

Technical Note 20 - 2

Generation of Biaxial Interaction Surfaces

Concrete Frame Design ACI-318-99

Column Design

linear strain diagram limits the maximum concrete strain, εc, at the extremity of the section, to 0.003 (ACI 10.2.3). The formulation is based consistently upon the general principles of ultimate strength design (ACI 10.3), and allows for any doubly symmetric rectangular, square, or circular column section. The stress in the steel is given by the product of the steel strain and the steel modulus of elasticity, εsEs, and is limited to the yield stress of the steel, fy (ACI 10.2.4). The area associated with each reinforcing bar is assumed to be placed at the actual location of the center of the bar and the algorithm does not assume any further simplifications with respect to distributing the area of steel over the cross section of the column, such as an equivalent steel tube or cylinder. See Figure 3. The concrete compression stress block is assumed to be rectangular, with a stress value of 0.85 f c' (ACI 10.2.7.1). See Figure 3. The interaction algorithm provides correction to account for the concrete area that is displaced by the reinforcement in the compression zone. The effects of the strength reduction factor, ϕ, are included in the generation of the interaction surfaces. The maximum compressive axial load is limited to ϕPn(max), where ϕPn(max) = 0.85ϕ[0.85 f c' (Ag-Ast)+fyAst] spiral column, ϕPn(max) = 0.80ϕ[0.85 f c' (Ag-Ast)+fyAst] tied column, ϕ ϕ = = 0.70 for tied columns, and 0.75 for spirally reinforced columns. (ACI 10.3.5.1) (ACI 10.3.5.2) (ACI 9.3.2.2) (ACI 9.3.2.2)

The value of ϕ used in the interaction diagram varies from ϕ(compression) to ϕ(flexure) based on the axial load. For low values of axial load, ϕ is increased linearly from ϕ(compression) to ϕ(flexure) as the ϕPn decreases from the smaller of ϕPb or 0.1 f c' Ag to zero, where ϕPb is the axial force at the balanced condition. The ϕ factor used in calculating ϕPn and ϕPb is the ϕ(compression). In cases involving axial tension, ϕ is always ϕ(flexure), which is 0.9 by default (ACI 9.3.2.2).

Generation of Biaxial Interaction Surfaces

Technical Note 20 - 3

Column Design

Concrete Frame Design ACI-318-99

Figure 2 Idealized Strain Distribution for Generation of Interaction Source

Technical Note 20 - 4

Generation of Biaxial Interaction Surfaces

Concrete Frame Design ACI-318-99

Column Design

Figure 3 Idealization of Stress and Strain Distribution in a Column Section

Calculate Column Capacity Ratio
The column capacity ratio is calculated for each load combination at each output station of each column. The following steps are involved in calculating the capacity ratio of a particular column for a particular load combination at a particular location: Determine the factored moments and forces from the analysis load cases and the specified load combination factors to give Pu, Mux, and Muy. Determine the moment magnification factors for the column moments. Apply the moment magnification factors to the factored moments. Determine whether the point, defined by the resulting axial load and biaxial moment set, lies within the interaction volume. The factored moments and corresponding magnification factors depend on the identification of the individual column as either “sway” or “non-sway.” The following three sections describe in detail the algorithms associated with this process.

Calculate Column Capacity Ratio

Technical Note 20 - 5

Column Design

Concrete Frame Design ACI-318-99

Determine Factored Moments and Forces
The factored loads for a particular load combination are obtained by applying the corresponding load factors to all the load cases, giving Pu, Mux, and Muy. The factored moments are further increased for non-sway columns, if required, to obtain minimum eccentricities of (0.6+0.03h) inches, where h is the dimension of the column in the corresponding direction (ACI 10.12.3.2).

Determine Moment Magnification Factors
The moment magnification factors are calculated separately for sway (overall stability effect), δs and for non-sway (individual column stability effect), δns. Also, the moment magnification factors in the major and minor directions are in general different (ACI 10.0, R10.13). The moment obtained from analysis is separated into two components: the sway (Ms) and the non-sway (Mns) components. The non-sway components, which are identified by “ns” subscripts, are predominantly caused by gravity load. The sway components are identified by the “s” subscripts. The sway moments are predominantly caused by lateral loads, and are related to the cause of side sway. For individual columns or column-members in a floor, the magnified moments about two axes at any station of a column can be obtained as M = Mns + δsMs. (ACI 10.13.3)

The factor δs is the moment magnification factor for moments causing side sway. The moment magnification factors for sway moments, δs, is taken as 1 because the component moments Ms and Mns are obtained from a “second order elastic (P-delta) analysis” (ACI R10.10, 10.10.1, R10.13, 10.13.4.1). The program assumes that it performs a P-delta analysis and, therefore, moment magnification factor δs for moments causing side-sway is taken as unity (ACI 10.10.2). For the P-delta analysis, the load should correspond to a load combination of 1.4 dead load + 1.7 live load (ACI 10.13.6). See also White and Hajjar (1991). The user should use reduction factors for the moment of inertias in the program as specified in ACI 10.11. The moment of inertia reduction for sustained lateral load involves a factor βd (ACI 10.11). This βd for sway frame in second-order analysis is different from the one that is defined later for non-sway moment magnification (ACI 10.0, R10.12.3, R10.13.4.1). The default moment of inertia factor in this program is 1.

Technical Note 20 - 6

Calculate Column Capacity Ratio

Concrete Frame Design ACI-318-99

Column Design

The computed moments are further amplified for individual column stability effect (ACI 10.12.3, 10.13.5) by the nonsway moment magnification factor, δns, as follows: Mc = δnsM, where (ACI 10.12.3)

Mc is the factored moment to be used in design. The non-sway moment magnification factor, δns, associated with the major or minor direction of the column is given by (ACI 10.12.3) δns = Cm ≤ 1.0, where Pu 1− 0.75Pc Ma ≥ 0.4, Mb (ACI 10.12.3)

Cm

= 0.6 +0.4

(ACI 10.12.3.1)

Ma and Mb are the moments at the ends of the column, and Mb is numerically larger than Ma. Ma / Mb is positive for single curvature bending and negative for double curvature bending. The above expression of Cm is valid if there is no transverse load applied between the supports. If transverse load is present on the span, or the length is overwritten, Cm=1. The user can overwrite Cm on an element-byelement basis. Pc = π 2 EI (kl u )2 , where (ACI 10.12.3)

k is conservatively taken as 1; however, the program allows the user to override this value (ACI 10.12.1). lu is the unsupported length of the column for the direction of bending considered. The two unsupported lengths are l22 and l33, corresponding to instability in the minor and major directions of the element, respectively. See Figure 4. These are the lengths

Calculate Column Capacity Ratio

Technical Note 20 - 7

Column Design

Concrete Frame Design ACI-318-99

Figure 4 Axes of Bending and Unsupported Length
between the support points of the element in the corresponding directions. EI is associated with a particular column direction: EI = 0.4E c I g 1 + βd , where (ACI 10.12.3)

βd = maximum factored axial sustained (dead) load
maximum factored axial total load

(ACI 10.0,R10.12.3)

The magnification factor, δns, must be a positive number and greater than one. Therefore, Pu must be less than 0.75Pc. If Pu is found to be greater than or equal to 0.75Pc, a failure condition is declared.

Technical Note 20 - 8

Calculate Column Capacity Ratio

Concrete Frame Design ACI-318-99

Column Design

The above calculations are performed for major and minor directions separately. That means that δs, δns, Cm, k, lu, EI, and Pc assume different values for major and minor directions of bending. If the program assumptions are not satisfactory for a particular member, the user can explicitly specify values of δs and δns.

Determine Capacity Ratio
As a measure of the stress condition of the column, a capacity ratio is calculated. The capacity ratio is basically a factor that gives an indication of the stress condition of the column with respect to the capacity of the column. Before entering the interaction diagram to check the column capacity, the moment magnification factors are applied to the factored loads to obtain Pu, Mux, and Muy. The point (Pu, Mux, Muy) is then placed in the interaction space shown as point L in Figure 5. If the point lies within the interaction volume, the column capacity is adequate; however, if the point lies outside the interaction volume, the column is overstressed. This capacity ratio is achieved by plotting the point L and determining the location of point C. The point C is defined as the point where the line OL (if extended outwards) will intersect the failure surface. This point is determined by three-dimensional linear interpolation between the points that define the failOL ure surface. See Figure 5. The capacity ratio, CR, is given by the ratio . OC If OL = OC (or CR=1), the point lies on the interaction surface and the column is stressed to capacity. If OL < OC (or CR<1), the point lies within the interaction volume and the column capacity is adequate. If OL > OC (or CR>1), the point lies outside the interaction volume and the column is overstressed. The maximum of all the values of CR calculated from each load combination is reported for each check station of the column along with the controlling Pu, Mux, and Muy set and associated load combination number.

Calculate Column Capacity Ratio

Technical Note 20 - 9

Column Design

Concrete Frame Design ACI-318-99

Figure 5 Geometric Representation of Column Capacity Ratio

Required Reinforcing Area
If the reinforcing area is not defined, the program computes the reinforcement that will give a column capacity ratio of one, calculated as described in the previous section entitled "Calculate Column Capacity Ratio."

Design Column Shear Reinforcement
The shear reinforcement is designed for each load combination in the major and minor directions of the column. The following steps are involved in designing the shear reinforcing for a particular column for a particular load combination resulting from shear forces in a particular direction:

Technical Note 20 - 10

Required Reinforcing Area

Concrete Frame Design ACI-318-99

Column Design

Determine the factored forces acting on the section, Pu and Vu. Note that Pu is needed for the calculation of Vc. Determine the shear force, Vc, that can be resisted by concrete alone. Calculate the reinforcement steel required to carry the balance. For Special and Intermediate moment resisting frames (Ductile frames), the shear design of the columns is also based on the Probable moment and nominal moment capacities of the members, respectively, in addition to the factored moments. Effects of the axial forces on the column moment capacities are included in the formulation. The following three sections describe in detail the algorithms associated with this process.

Determine Section Forces
In the design of the column shear reinforcement of an Ordinary moment resisting concrete frame, the forces for a particular load combination, namely, the column axial force, Pu, and the column shear force, Vu, in a particular direction are obtained by factoring the program analysis load cases with the corresponding load combination factors. In the shear design of Special moment resisting frames (i.e., seismic design), the column is checked for capacity shear in addition to the requirement for the Ordinary moment resisting frames. The capacity shear force in a column, Vp, in a particular direction is calculated from the probable moment capacities of the column associated with the factored axial force acting on the column. For each load combination, the factored axial load, Pu, is calculated. Then,
+ − the positive and negative moment capacities, Mu and Mu , of the column

in a particular direction under the influence of the axial force Pu is calculated using the uniaxial interaction diagram in the corresponding direction. The design shear force, Vu, is then given by (ACI 21.4.5.1) Vu = Vp + VD+L (ACI 21.4.5.1)

where, Vp is the capacity shear force obtained by applying the calculated probable ultimate moment capacities at the two ends of the column acting

Design Column Shear Reinforcement

Technical Note 20 - 11

Column Design

Concrete Frame Design ACI-318-99

in two opposite directions. Therefore, Vp is the maximum of VP1 and VP2 , where

VP1 = VP2 =

− + MI + M J , and L + − MI + M J , where L

+ − MI , MI ,

= Positive and negative moment capacities at end I of the column using a steel yield stress value of αfy and no ϕ factors (ϕ = 1.0),

+ − MJ , MJ ,

= Positive and negative moment capacities at end J of the column using a steel yield stress value of αfy and no ϕ factors (ϕ = 1.0), and

L

= Clear span of column.

For Special moment resisting frames α is taken as 1.25 (ACI 10.0, R21.4.5.1). VD+L is the contribution of shear force from the in-span distribution of gravity loads. For most of the columns, it is zero. For Intermediate moment resisting frames, the shear capacity of the column is also checked for the capacity shear based on the nominal moment capacities at the ends and the factored gravity loads, in addition to the check required for Ordinary moment resisting frames. The design shear force is taken to be the minimum of that based on the nominal (ϕ = 1.0) moment capacity and modified factored shear force. The procedure for calculating nominal moment capacity is the same as that for computing the probable moment capacity for special moment resisting frames, except that α is taken equal to 1 rather than 1.25 (ACI 21.10.3.a, R21.10). The modified factored shear forces are based on the specified load factors, except the earthquake load factors are doubled (ACI 21.10.3.b).

Determine Concrete Shear Capacity
Given the design force set Pu and Vu, the shear force carried by the concrete, Vc, is calculated as follows:

Technical Note 20 - 12

Design Column Shear Reinforcement

Concrete Frame Design ACI-318-99

Column Design

If the column is subjected to axial compression, i.e., Pu is positive,  Pu Vc = 2 f c' 1 +  2,000 Ag  f c' ≤ 100 psi, and Vc ≤ 3.5 f c'  1 + Pu  500 Ag    Acv.     Acv, where   (ACI 11.3.1.2)

(ACI 11.1.2)

(ACI 11.3.2.2)

The term Pu / Ag must have psi units. Acv is the effective shear area, which is shown shaded in Figure 6. For circular columns, Acv is taken to be equal to the gross area of the section (ACI 11.3.3, R11.3.3). If the column is subjected to axial tension, Pu is negative Vc = 2 f c'  1 + Pu  500 Ag    Acv ≥ 0   (ACI 11.3.2.3)

For Special moment resisting concrete frame design, Vc is set to zero if the factored axial compressive force, Pu, including the earthquake effect, is small (Pu < f c' Ag / 20) and if the shear force contribution from earthquake, VE, is more than half of the total factored maximum shear force over the length of the member Vu (VE ≥ 0.5Vu) (ACI 21.4.5.2).

Determine Required Shear Reinforcement
Given Vu and Vc, the required shear reinforcement in the form of stirrups or ties within a spacing, s, is given for rectangular and circular columns by Av = (Vu / ϕ − Vc )s , for rectangular columns and f ys d (Vu / ϕ − Vc )s , for circular columns. f ys (0.8D) (ACI 11.5.6.1, 11.5.6.2)

Av =

(ACI 11.5.6.3, 11.3.3)

Vu is limited by the following relationship. (Vu / ϕ-Vc) ≤ 8 f c' Acv (ACI 11.5.6.9)

Design Column Shear Reinforcement

Technical Note 20 - 13

Column Design

Concrete Frame Design ACI-318-99

Figure 6 Shear Stress Area, Acv
Otherwise, redimensioning of the concrete section is required. Here ϕ, the strength reduction factor, is 0.85 (ACI 9.3.2.3). The maximum of all the calculated Av values obtained from each load combination are reported for the major and minor directions of the column, along with the controlling shear force and associated load combination label. The column shear reinforcement requirements reported by the program are based purely on shear strength consideration. Any minimum stirrup requirements to satisfy spacing considerations or transverse reinforcement volumetric considerations must be investigated independently of the program by the user.

Technical Note 20 - 14

Design Column Shear Reinforcement

Concrete Frame Design ACI-318-99

Column Design

Reference
White, D.W. and J.F. Hajjar. 1991. Application of Second-Order Elastic Analysis in LRFD: Research to Practice. Engineering Journal. American Institute of Steel Construction, Inc. Vol. 28. No. 4.

Reference

Technical Note 20 - 15

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN ACI-318-99

Technical Note 21

Beam Design
This Technical Note describes how this program completes beam design when the ACI 318-99 code is selected. The program calculates and reports the required areas of steel for flexure and shear based on the beam moments, shears, load combination factors and other criteria described herein.

Overview
In the design of concrete beams, the program calculates and reports the required areas of steel for flexure and shear based on the beam moments, shears, load combination factors, and other criteria described below. The reinforcement requirements are calculated at a user-defined number of check/design stations along the beam span. All beams are designed for major direction flexure and shear only. Effects resulting from any axial forces, minor direction bending, and torsion that may exist in the beams must be investigated independently by the user. The beam design procedure involves the following steps: Design beam flexural reinforcement Design beam shear reinforcement

Design Beam Flexural Reinforcement
The beam top and bottom flexural steel is designed at check/design stations along the beam span. The following steps are involved in designing the flexural reinforcement for the major moment for a particular beam for a particular section: Determine the maximum factored moments Determine the reinforcing steel

Overview

Technical Note 21 - 1

Beam Design

Concrete Frame Design ACI-318-99

Determine Factored Moments
In the design of flexural reinforcement of Special, Intermediate, or Ordinary moment resisting concrete frame beams, the factored moments for each load combination at a particular beam section are obtained by factoring the corresponding moments for different load cases with the corresponding load factors.
+ The beam section is then designed for the maximum positive M u and maxi− mum negative M u factored moments obtained from all of the load combina-

tions. Negative beam moments produce top steel. In such cases, the beam is always designed as a rectangular section. Positive beam moments produce bottom steel. In such cases, the beam may be designed as a Rectangular- or a T-beam.

Determine Required Flexural Reinforcement
In the flexural reinforcement design process, the program calculates both the tension and compression reinforcement. Compression reinforcement is added when the applied design moment exceeds the maximum moment capacity of a singly reinforced section. The user has the option of avoiding the compression reinforcement by increasing the effective depth, the width, or the grade of concrete. The design procedure is based on the simplified rectangular stress block as shown in Figure 1 (ACI 10.2). It is assumed that the compression carried by concrete is less than 0.75 times that which can be carried at the balanced condition (ACI 10.3.3). When the applied moment exceeds the moment capacity at this designed balanced condition, the area of compression reinforcement is calculated assuming that the additional moment will be carried by compression and additional tension reinforcement. The design procedure used by this program for both rectangular and flanged sections (L- and T-beams) is summarized below. It is assumed that the design ultimate axial force does not exceed 0.1 f c' Ag (ACI 10.3.3); hence, all the beams are designed for major direction flexure and shear only.

Technical Note 21 - 2

Design Beam Flexural Reinforcement

Concrete Frame Design ACI-318-99

Beam Design

Figure 1 Design of Rectangular Beam Section

Design for Rectangular Beam
In designing for a factored negative or positive moment, Mu (i.e., designing top or bottom steel), the depth of the compression block is given by a (see Figure 1), where, a=dd2 − 2 Mu
1 0.85f c ϕb

,

(ACI 10.2.7.1)

where, the value of ϕ is 0.90 (ACI 9.3.2.1) in the above and the following equations. Also β1 and cb are calculated as follows:  f ' − 4,000   , 0.65 ≤ β1 ≤ 0.85, β1 = 0.85-0.05  c  1,000    cb = εc Es 87,000 d = d. 87,000 + f y ε c E s + fy (ACI 10.2.7.3)

(ACI 10.2.3, 10.2.4)

Design Beam Flexural Reinforcement

Technical Note 21 - 3

Beam Design

Concrete Frame Design ACI-318-99

The maximum allowed depth of the compression block is given by amax = 0.75β1cb. (ACI 10.2.7.1, 10.3.3)

If a ≤ amax, the area of tensile steel reinforcement is then given by As = Mu a  ϕf y  d −  2  .

This steel is to be placed at the bottom if Mu is positive, or at the top if Mu is negative. If a > amax, compression reinforcement is required (ACI 10.3.3) and is calculated as follows:
−

The compressive force developed in concrete alone is given by C = 0.85 f c' bamax, and (ACI 10.2.7.1)

the moment resisted by concrete compression and tensile steel is a  Muc = C  d − max  2 
−

  ϕ.  

Therefore the moment resisted by compression steel and tensile steel is Mus = Mu - Muc.

−

So the required compression steel is given by
' As =

M us f s' (d − d' )ϕ

, where

 c − d'  f s' = 0.003Es  .  c 
−

(ACI 10.2.4)

The required tensile steel for balancing the compression in concrete is

Technical Note 21 - 4

Design Beam Flexural Reinforcement

Concrete Frame Design ACI-318-99

Beam Design

As1 =

M uc a   f y d − max  ϕ 2  

, and

the tensile steel for balancing the compression in steel is given by As2 = M us . f y (d − d' )ϕ

−

Therefore, the total tensile reinforcement, As = As1 + As2, and total
' ' compression reinforcement is As . As is to be placed at bottom and As

is to be placed at top if Mu is positive, and vice versa if Mu is negative.

Design for T-Beam
In designing for a factored negative moment, Mu (i.e., designing top steel), the calculation of the steel area is exactly the same as above, i.e., no T-Beam data is to be used. See Figure 2. If Mu > 0, the depth of the compression block is given by a=dd2 − 2Mu 0.85f c' ϕbf .

The maximum allowed depth of compression block is given by amax = 0.75β1cb. (ACI 10.2.7.1, 10.3.3)

•

If a ≤ ds, the subsequent calculations for As are exactly the same as previously defined for the rectangular section design. However, in this case the width of the compression flange is taken as the width of the beam for analysis. Compression reinforcement is required if a > amax. If a > ds, calculation for As is performed in two parts. The first part is for balancing the compressive force from the flange, Cf, and the second part is for balancing the compressive force from the web, Cw, as shown in Figure 2. Cf is given by Cf = 0.85 f c' (bf - bw)ds.

•

Design Beam Flexural Reinforcement

Technical Note 21 - 5

Beam Design

Concrete Frame Design ACI-318-99

Figure 2 Design of a T-Beam Section
Therefore, As1 = given by d   Muf = Cf  d − s  ϕ.  2    Again, the value for ϕ is ϕ(flexure), which is 0.90 by default. Therefore, the balance of the moment, Mu to be carried by the web is given by Muw = Mu - Muf. The web is a rectangular section of dimensions bw and d, for which the design depth of the compression block is recalculated as a1 = d d2 − 2Muw 0.85f ci ϕbw . Cf fy and the portion of Mu that is resisted by the flange is

If a1 ≤ amax, the area of tensile steel reinforcement is then given by As2 = Muw a   ϕf y  d − 1   2    , and

Technical Note 21 - 6

Design Beam Flexural Reinforcement

Concrete Frame Design ACI-318-99

Beam Design

As = As1 + As2. This steel is to be placed at the bottom of the T-beam. If a1 > amax, compression reinforcement is required (ACI 10.3.3) and is calculated as follows:
−

The compressive force in web concrete alone is given by C = 0.85 f c' bamax. (ACI 10.2.7.1)

−

Therefore, the moment resisted by concrete web and tensile steel is a   Muc = C  d − max ϕ , and  2    the moment resisted by compression steel and tensile steel is Mus = Muw - Muc.

−

Therefore, the compression steel is computed as
' As =

Mus f s' (d − d' )ϕ

, where

 c − d'  f s' = 0.003Es  .  c 
−

(ACI 10.2.4)

The tensile steel for balancing compression in web concrete is As2 = Muc , and amax )ϕ f y (d − 2

the tensile steel for balancing compression in steel is As3 = Mus . f y (d − d' )ϕ

Design Beam Flexural Reinforcement

Technical Note 21 - 7

Beam Design

Concrete Frame Design ACI-318-99

−

The total tensile reinforcement, As = As1 + As2 + As3, and total
' compression reinforcement is As . As is to be placed at bottom and ' As is to be placed at top.

Minimum Tensile Reinforcement
The minimum flexural tensile steel provided in a rectangular section in an Ordinary moment resisting frame is given by the minimum of the two following limits:  3 f ' 200   c As ≥ max  bw d and bw d  or fy fy     As ≥ (4/3)As(required). (ACI 10.5.1) (ACI 10.5.3)

Special Consideration for Seismic Design
For Special moment resisting concrete frames (seismic design), the beam design satisfies the following additional conditions (see also Table 1): The minimum longitudinal reinforcement shall be provided at both the top and bottom. Any of the top and bottom reinforcement shall not be less than As(min) (ACI 21.3.2.1). 3 f '  200   c As(min) ≥ max  bw d and bw d  or fy fy     As(min) ≥ 4 As(required). 3 (ACI 10.5.1)

(ACI 10.5.3)

The beam flexural steel is limited to a maximum given by As ≤ 0.025 bwd. (ACI 21.3.2.1)

At any end (support) of the beam, the beam positive moment capacity (i.e., associated with the bottom steel) would not be less than 1/2 of the beam negative moment capacity (i.e., associated with the top steel) at that end (ACI 21.3.2.2). Neither the negative moment capacity nor the positive moment capacity at any of the sections within the beam would be less than 1/4 of the

Technical Note 21 - 8

Design Beam Flexural Reinforcement

Concrete Frame Design ACI-318-99

Beam Design

maximum of positive or negative moment capacities of any of the beam end (support) stations (ACI 21.3.2.2). For Intermediate moment resisting concrete frames (i.e., seismic design), the beam design would satisfy the following conditions: At any support of the beam, the beam positive moment capacity would not be less than 1/3 of the beam negative moment capacity at that end (ACI 21.10.4.1). Neither the negative moment capacity nor the positive moment capacity at any of the sections within the beam would be less than 1/5 of the maximum of positive or negative moment capacities of any of the beam end (support) stations (ACI 21.10.4.1).

Design Beam Shear Reinforcement
The shear reinforcement is designed for each load combination at a user defined number of stations along the beam span. The following steps are involved in designing the shear reinforcement for a particular beam for a particular load combination at a particular station due to the beam major shear:

• • •

Determine the factored shear force, Vu. Determine the shear force, Vc, that can be resisted by the concrete. Determine the reinforcement steel required to carry the balance.

For Special and Intermediate moment resisting frames (ductile frames), the shear design of the beams is also based upon the probable and nominal moment capacities of the members, respectively, in addition to the factored load design. The following three sections describe in detail the algorithms associated with this process.

Design Beam Shear Reinforcement

Technical Note 21 - 9

Beam Design

Concrete Frame Design ACI-318-99

Table 1 Design Criteria Table
Type of Check/ Design Column Check (interaction) Column Design (interaction) Ordinary Moment Resisting Frames (non-Seismic) NLDa Combinations Intermediate Moment Resisting Frames (Seismic) NLDa Combinations Special Moment Resisting Frames (Seismic) NLDa Combinations

NLDa Combinations 1% < ρ < 8%

NLDa Combinations 1% < ρ < 8% Modified NLDa Combinations (earthquake loads doubled) Column capacity ϕ = 1.0 and α = 1.0

NLDa Combinations α = 1.0 1% < ρ < 6% NLDa Combinations Column shear capacity ϕ = 1.0 and α = 1.25 NLDa Combinations ρ ≤ 0.025 ρ≥
3 f c' fy

Column Shears

NLDa Combinations

Beam Design Flexure

NLDa Combinations

NLDa Combinations

, ρ ≥ 200
fy

Beam Min. Moment Override Check

+ M uEND ≥

No Requirement

+ MuSPAN
− M uSPAN

{ 1 ≥ max{ M 5

1 − M u END 3 1 + − ≥ max M u , M u 5

+ M uEND ≥

+ − u , M u END

} }

END

+ MuSPAN
− MuSPAN

{ } 1 ≥ max{ , M } M 4
− u

1 − M u END 2 1 + − ≥ max Mu , Mu 4

END

− u END

Beam Design Shear

NLDa Combinations

Modified NLDa Combinations (earthquake loads doubled) Beam Capacity Shear (Vp) with α = 1.0 and ϕ = 1.0 plus VD+L No Requirement

NLDa Combinations Beam Capacity Shear (Vp) with α = 1.25 and ϕ = 1.0 plus VD+L Vc = 0 Checked for shear

Joint Design Beam/Column Capacity Ratio

No Requirement

No Requirement

No Requirement

Reported in output file

NLDa = Number of specified loading

Technical Note 21 - 10

Design Beam Shear Reinforcement

Concrete Frame Design ACI-318-99

Beam Design

Determine Shear Force and Moment
•
In the design of the beam shear reinforcement of an Ordinary moment resisting concrete frame, the shear forces and moments for a particular load combination at a particular beam section are obtained by factoring the associated shear forces and moments with the corresponding load combination factors. In the design of Special moment resisting concrete frames (i.e., seismic design), the shear capacity of the beam is also checked for the capacity shear resulting from the probable moment capacities at the ends and the factored gravity load. This check is performed in addition to the design check required for Ordinary moment resisting frames. The capacity shear force, Vp, is calculated from the probable moment capacities of each end of the beam and the gravity shear forces. The procedure for calculating the design shear force in a beam from probable moment capacity is the same as that described for a column in section “Design Column Shear Reinforcement” of Concrete Frame Design ACI318-99 Technical Note 20 Column Design. See also Table 1 for details. The design shear force Vu is then given by (ACI 21.3.4.1) Vu = Vp + VD+L (ACI 21.3.4.1)

•

where Vp is the capacity shear force obtained by applying the calculated probable ultimate moment capacities at the two ends of the beams acting in two opposite directions. Therefore, Vp is the maximum of VP1 and VP2 , where

VP1 VP2
− MI

=

− + MI + MJ , and L + − MI + MJ , where L

=

= Moment capacity at end I, with top steel in tension, using a steel yield stress value of αfy and no ϕ factors (ϕ = 1.0),

+ MJ

= Moment capacity at end J, with bottom steel in tension, using a steel yield stress value of αfy and no ϕ factors (ϕ = 1.0),

Design Beam Shear Reinforcement

Technical Note 21 - 11

Beam Design

Concrete Frame Design ACI-318-99

+ MI

= Moment capacity at end I, with bottom steel in tension, using a steel yield stress value of αfy and no ϕ factors (ϕ = 1.0),

− MJ

= Moment capacity at end J, with top steel in tension, using a
steel yield stress value of αfy and no ϕ factors (ϕ = 1.0), and = Clear span of beam.

L

For Special moment resisting frames α is taken as 1.25 (ACI 21.0, R21.3.4.1). VD+L is the contribution of shear force from the in-span distribution of gravity loads.

•

For Intermediate moment resisting frames, the shear capacity of the beam is also checked for the capacity shear based on the nominal moment capacities at the ends and the factored gravity loads, in addition to the check required for Ordinary moment resisting frames. The design shear force in beams is taken to be the minimum of that based on the nominal moment capacity and modified factored shear force. The procedure for calculating nominal (ϕ = 1.0) moment capacity is the same as that for computing the probable moment capacity for Special moment resisting frames, except that α is taken equal to 1 rather than 1.25 (ACI 21.10.3.a, R21.10). The modified factored shear forces are based on the specified load factors, except the earthquake load factors are doubled (ACI 21.10.3.b). The computation of the design shear force in a beam of an Intermediate moment resisting frame is the same as described for columns in section “Determine Section Forces” of Concrete Frame Design ACI318-99 Technical Note 20 Column Design. See also Table 1 for details.

Determine Concrete Shear Capacity
The allowable concrete shear capacity is given by Vc = 2 f c' bwd. (ACI 11.3.1.1)

For Special moment resisting frame concrete design, Vc is set to zero if both the factored axial compressive force, including the earthquake effect Pu, is less than f c' Ag/20 and the shear force contribution from earthquake VE is more than half of the total maximum shear force over the length of the member Vu (i.e., VE ≥ 0.5Vu) (ACI 21.3.4.2).

Technical Note 21 - 12

Design Beam Shear Reinforcement

Concrete Frame Design ACI-318-99

Beam Design

Determine Required Shear Reinforcement
Given Vu and Vc, the required shear reinforcement in area/unit length is calculated as Av = (Vu / ϕ − Vc )s . f ys d (ACI 11.5.6.1, 11.5.6.2)

The shear force resisted by steel is limited by (Vu / ϕ - Vc) ≤ 8 f c' bd. (ACI 11.5.6.9)

Otherwise, redimensioning of the concrete section is required. Here, ϕ, the strength reduction factor for shear, is 0.85 by default (ACI 9.3.2.3). The maximum of all the calculated Av values, obtained from each load combination, is reported along with the controlling shear force and associated load combination number. The beam shear reinforcement requirements displayed by the program are based purely on shear strength considerations. Any minimum stirrup requirements to satisfy spacing and volumetric considerations must be investigated independently of the program by the user.

Design Beam Shear Reinforcement

Technical Note 21 - 13

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN ACI318-99

Technical Note 22 Joint Design
This Technical Note explains how the program performs a rational analysis of the beam-column panel zone to determine the shear forces that are generated in a joint. The program then checks this against design shear strength.

Overview
To ensure that the beam-column joint of special moment resisting frames possesses adequate shear strength, the program performs a rational analysis of the beam-column panel zone to determine the shear forces that are generated in the joint. The program then checks this against design shear strength. Only joints having a column below the joint are designed. The material properties of the joint are assumed to be the same as those of the column below the joint. The joint analysis is completed in the major and the minor directions of the column. The joint design procedure involves the following steps: Determine the panel zone design shear force, Vuh Determine the effective area of the joint Check panel zone shear stress The algorithms associated with these three steps are described in detail in the following three sections.

Determine the Panel Zone Shear Force
Figure 1 illustrates the free body stress condition of a typical beam-column intersection for a column direction, major or minor.

Overview

Technical Note 22 - 1

Joint Design

Concrete Frame Design ACI318-99

Figure 1 Beam-Column Joint Analysis

Technical Note 22 - 2

Determine the Panel Zone Shear Force

Concrete Frame Design ACI318-99

Joint Design

The force Vuh is the horizontal panel zone shear force that is to be calculated. The forces that act on the joint are Pu, Vu, MuL and MuR. The forces Pu and Vu are axial force and shear force, respectively, from the column framing into the top of the joint. The moments MuL and MuR are obtained from the beams framing into the joint. The program calculates the joint shear force Vuh by resolving the moments into C and T forces. Noting that TL = CL and TR = CR, Vuh = TL + TR - Vu The location of C or T forces is determined by the direction of the moment. The magnitude of C or T forces is conservatively determined using basic principles of ultimate strength theory, ignoring compression reinforcement as follows. The program first calculates the maximum compression, Cmax, and the maximum moment, Mmax, that can be carried by the beam. C max = 0.85f ' c bd Mmax = C max d 2

Then the program conservatively determines C and T forces as follows:

 abs( M )   C = T = C max 1 − 1 −  M max   
The program resolves the moments and the C and T forces from beams that frame into the joint in a direction that is not parallel to the major or minor directions of the column along the direction that is being investigated, thereby contributing force components to the analysis. Also, the program calculates the C and T for the positive and negative moments, considering the fact that the concrete cover may be different for the direction of moment. In the design of special moment resisting concrete frames, the evaluation of the design shear force is based on the moment capacities (with reinforcing steel overstrength factor, α, and no ϕ factors) of the beams framing into the joint (ACI 21.5.1.1, UBC 1921.5.1.1). The C and T force are based on these moment capacities. The program calculates the column shear force Vu from the beam moment capacities, as follows:

Determine the Panel Zone Shear Force

Technical Note 22 - 3

Joint Design

Concrete Frame Design ACI318-99

Vu =

Mu + Mu H

L

R

See Figure 2. It should be noted that the points of inflection shown on Figure 2 are taken as midway between actual lateral support points for the columns. If there is no column at the top of the joint, the shear force from the top of the column is taken as zero. The effects of load reversals, as illustrated in Case 1 and Case 2 of Figure 1, are investigated and the design is based on the maximum of the joint shears obtained from the two cases.

Determine the Effective Area of Joint
The joint area that resists the shear forces is assumed always to be rectangular in plan view. The dimensions of the rectangle correspond to the major and minor dimensions of the column below the joint, except if the beam framing into the joint is very narrow. The effective width of the joint area to be used in the calculation is limited to the width of the beam plus the depth of the column. The area of the joint is assumed not to exceed the area of the column below. The joint area for joint shear along the major and minor directions is calculated separately (ACI R21.5.3). It should be noted that if the beam frames into the joint eccentrically, the above assumptions may be unconservative and the user should investigate the acceptability of the particular joint.

Check Panel Zone Shear Stress
The panel zone shear stress is evaluated by dividing the shear force Vuh by the effective area of the joint and comparing it with the following design shear strengths (ACI 21.5.3, UBC 1921.5.3):

v =

{

20ϕ 15ϕ 12ϕ

f 'c f 'c f 'c

for joints confirmed on all four sides for joints confirmed on three faces or on two opposite faces for all other joints

Technical Note 22 - 4

Determine the Effective Area of Joint

Concrete Frame Design ACI318-99

Joint Design

Figure 2 Column Shear Force Vu

where ϕ = 0.85 (by default).

(ACI 9.3.2.3, UBC 1909.3.2.3,1909.3.4.1)

A beam that frames into a face of a column at the joint is considered in this program to provide confinement to the joint if at least three-quarters of the face of the joint is covered by the framing member (ACI 21.5.3.1, UBC 1921.5.3.1).

Determine the Effective Area of Joint

Technical Note 22 - 5

Joint Design

Concrete Frame Design ACI318-99

For light-weight aggregate concrete, the design shear strength of the joint is reduced in the program to at least three-quarters of that of the normal weight concrete by replacing the f c' with (ACI 21.5.3.2, UBC 1921.5.3.2)

minf cs, factor f c' ,3 / 4 f c'     

For joint design, the program reports the joint shear, the joint shear stress, the allowable joint shear stress and a capacity ratio.

Beam/Column Flexural Capacity Ratios
At a particular joint for a particular column direction, major or minor, the program will calculate the ratio of the sum of the beam moment capacities to the sum of the column moment capacities (ACI 21.4.2.2). ∑Me ≥ 6 ∑Mg 5 (ACI 21.4.2.2)

The capacities are calculated with no reinforcing overstrength factor, α , and including ϕ factors. The beam capacities are calculated for reversed situations (Cases 1 and 2) as illustrated in Figure 1 and the maximum summation obtained is used. The moment capacities of beams that frame into the joint in a direction that is not parallel to the major or minor direction of the column are resolved along the direction that is being investigated and the resolved components are added to the summation. The column capacity summation includes the column above and the column below the joint. For each load combination, the axial force, Pu, in each of the columns is calculated from the program analysis load combinations. For each load combination, the moment capacity of each column under the influence of the corresponding axial load Pu is then determined separately for the major and minor directions of the column, using the uniaxial column interaction diagram; see Figure 3. The moment capacities of the two columns are added to give the capacity summation for the corresponding load combination. The maximum capacity summations obtained from all of the load combinations is used for the beam/column capacity ratio.

Technical Note 22 - 6

Beam/Column Flexural Capacity Ratios

Concrete Frame Design ACI318-99

Joint Design

The beam/column flexural capacity ratios are only reported for Special Moment-Resisting Frames involving seismic design load combinations. If this ratio is greater than 5/6, a warning message is printed in the output file.

Figure 3 Moment Capacity Mu at a Given Axial Load Pu

Beam/Column Flexural Capacity Ratios

Technical Note 22 - 7

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN ACI318-99

Technical Note 23

Input Data
This Technical Note describes the concrete frame design input data for ACI318-99. The input can be printed to a printer or to a text file when you click the File menu > Print Tables > Concrete Frame Design command. A printout of the input data provides the user with the opportunity to carefully review the parameters that have been input into the program and upon which program design is based. Further information about using the Print Design Tables form is presented at the end of this Technical Note.

Input Data
The program provides the printout of the input data in a series of tables. The column headings for input data and a description of what is included in the columns of the tables are provided in Table 1 of this Technical Note.

Table 1 Concrete Frame Design Input Data
COLUMN HEADING Combo Type Case Factor DESCRIPTION Design load combination. See Technical Note 8. Load type: dead, live, superimposed dead, earthquake, wind, snow, reduced live load, other. Name of load case. Load combination scale factor. Bending strength reduction factor. Tensile strength reduction factor. Compressive strength reduction factor for tied columns. Compressive strength reduction factor for reinforced columns. Shear strength reduction factor.

Load Combination Multipliers

Code Preferences
Phi_bending Phi_tension Phi_compression (Tied) Phi_compression (Spiral) Phi_shear

Input Data

Technical Note 23 - 1

Input Data

Concrete Frame Design ACI318-99

Table 1 Concrete Frame Design Input Data
COLUMN HEADING DESCRIPTION Concrete, steel, other. Isotropic or orthotropic.

Material Property Data
Material Name Material Type Design Type Modulus of Elasticity Poisson's Ratio Thermal Coeff Shear Modulus Coefficient of thermal expansion.

Material Property Mass and Weight
Material Name Mass Per Unit Vol Weight Per Unit Vol Material Name Lightweight Concrete Concrete FC Rebar FY Rebar FYS Lightwt Reduc Fact Concrete compressive strength. Bending reinforcing steel yield strength. Shear reinforcing steel yield strength. Shear strength reduction factor for light weight concrete; default = 1.0. Label applied to section. Material label. Concrete, steel, other. Used to calculate self-mass of structure. Used to calculate self-weight of structure. Concrete, steel, other.

Material Design Data for Concrete Materials

Concrete Column Property Data
Section Label Mat Label Column Depth Column Width Rebar Pattern Concrete Cover Bar Area Layout of main flexural reinforcing steel. Minimum clear concrete cover. Area of individual reinforcing bar to be used.

Technical Note 23 - 2

Table 1 Concrete Frame Design Input Data

Concrete Frame Design ACI318-99

Input Data

Table 1 Concrete Frame Design Input Data
COLUMN HEADING Story ID Column Line Section ID Framing Type RLLF Factor L_Ratio Major L_Ratio Minor K Major K Minor Story ID Bay ID Section ID Framing type RLLF Factor L_Ratio Major L_Ratio Minor Unbraced length about major axis. Unbraced length about minor axis. Unbraced length about major axis. Unbraced length about minor axis. Effective length factor; default = 1.0. Effective length factor; default = 1.0. Story level at which beam occurs. Grid lines locating beam. Section number assigned to beam. Lateral or gravity. DESCRIPTION Column assigned to story level at top of column. Grid line. Name of section assigned to column. Lateral or gravity.

Concrete Column Design Element Information

Concrete Beam Design Element Information

Using the Print Design Tables Form
To print concrete frame design input data directly to a printer, use the File menu > Print Tables > Concrete Frame Design command and click the check box on the Print Design Tables form. Click the OK button to send the print to your printer. Click the Cancel button rather than the OK button to cancel the print. Use the File menu > Print Setup command and the Setup>> button to change printers, if necessary. To print concrete frame design input data to a file, click the Print to File check box on the Print Design Tables form. Click the Filename>> button to change

Using the Print Design Tables Form

Technical Note 23 - 3

Input Data

Concrete Frame Design ACI318-99

the path or filename. Use the appropriate file extension for the desired format (e.g., .txt, .xls, .doc). Click the OK buttons on the Open File for Printing Tables form and the Print Design Tables form to complete the request. Note: The File menu > Display Input/Output Text Files command is useful for displaying output that is printed to a text file. The Append check box allows you to add data to an existing file. The path and filename of the current file is displayed in the box near the bottom of the Print Design Tables form. Data will be added to this file. Or use the Filename>> button to locate another file, and when the Open File for Printing Tables caution box appears, click Yes to replace the existing file. If you select a specific frame element(s) before using the File menu > Print Tables > Concrete Frame Design command, the Selection Only check box will be checked. The print will be for the selected beam(s) only.

Technical Note 23 - 4

Using the Print Design Tables Form

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN ACI318-99

Technical Note 24

Output Details
This Technical Note describes the concrete frame design output for ACI318-99 that can be printed to a printer or to a text file. The design output is printed when you click the File menu > Print Tables > Concrete Frame Design command and select Output Summary on the Print Design Tables form. Further information about using the Print Design Tables form is presented at the end of this Technical Note. The program provides the output data in a series of tables. The column headings for output data and a description of what is included in the columns of the tables are provided in Table 1 of this Technical Note.

Table 1 Concrete Column Design Output
COLUMN HEADING Story ID Column Line Section ID Station ID DESCRIPTION Column assigned to story level at top of column. Grid lines. Name of section assigned to column.

Biaxial P-M Interaction and Shear Design of Column-Type Elements

Required Reinforcing
Longitudinal Combo Shear22 Combo Shear33 Area of longitudinal reinforcing required. Load combination for which the reinforcing is designed. Shear reinforcing required. Load combination for which the reinforcing is designed. Shear reinforcing required.

Table 1 Concrete Column Design Output

Technical Note 24 - 1

Output Details

Concrete Frame Design ACI318-99

Table 1 Concrete Column Design Output
COLUMN HEADING Combo DESCRIPTION Load combination for which the reinforcing is designed.

Table 2 Concrete Column Joint Output
COLUMN HEADING DESCRIPTION Beam to Column Capacity Ratios and Joint Shear Capacity Check Story ID Column Line Section ID Story level at which joint occurs. Grid line. Assigned section name.

Beam-Column Capacity Ratios Major Combo Ratio of beam moment capacity to column capacity. Load combination upon which the ratio of beam moment capacity to column capacity is based. Ratio of beam moment capacity to column capacity. Load combination upon which the ratio of beam moment capacity to column capacity is based.

Minor Combo

Joint Shear Capacity Ratios Major Combo Ratio of factored load versus allowed capacity. Load combination upon which the ratio of factored load versus allowed capacity is based. Ratio of factored load versus allowed capacity. Load combination upon which the ratio of factored load versus allowed capacity is based.

Minor Combo

Technical Note 24 - 2

Table 2 Concrete Column Joint Output

Concrete Frame Design ACI318-99

Output Details

Using the Print Design Tables Form
To print concrete frame design input data directly to a printer, use the File menu > Print Tables > Concrete Frame Design command and click the check box on the Print Design Tables form. Click the OK button to send the print to your printer. Click the Cancel button rather than the OK button to cancel the print. Use the File menu > Print Setup command and the Setup>> button to change printers, if necessary. To print concrete frame design input data to a file, click the Print to File check box on the Print Design Tables form. Click the Filename>> button to change the path or filename. Use the appropriate file extension for the desired format (e.g., .txt, .xls, .doc). Click the OK buttons on the Open File for Printing Tables form and the Print Design Tables form to complete the request. Note: The File menu > Display Input/Output Text Files command is useful for displaying output that is printed to a text file. The Append check box allows you to add data to an existing file. The path and filename of the current file is displayed in the box near the bottom of the Print Design Tables form. Data will be added to this file. Or use the Filename>> button to locate another file, and when the Open File for Printing Tables caution box appears, click Yes to replace the existing file. If you select a specific frame element(s) before using the File menu > Print Tables > Concrete Frame Design command, the Selection Only check box will be checked. The print will be for the selected beam(s) only.

Using the Print Design Tables Form

Technical Note 24 - 3


								
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