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                          ETABS
     Integrated Building Design Software


                   Steel Joist Design Manual




Computers and Structures, Inc.                    Version 8
Berkeley, California, USA                      January 2002
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CONSIDERABLE TIME, EFFORT AND EXPENSE HAVE GONE INTO THE
DEVELOPMENT AND DOCUMENTATION OF ETABS. THE PROGRAM HAS
BEEN THOROUGHLY TESTED AND USED. IN USING THE PROGRAM,
HOWEVER, THE USER ACCEPTS AND UNDERSTANDS THAT NO WARRANTY
IS EXPRESSED OR IMPLIED BY THE DEVELOPERS OR THE DISTRIBUTORS
ON THE ACCURACY OR THE RELIABILITY OF THE PROGRAM.

THIS PROGRAM IS A VERY PRACTICAL TOOL FOR THE DESIGN/CHECK OF
STEEL STRUCTURES. HOWEVER, THE USER MUST THOROUGHLY READ THE
MANUAL AND CLEARLY RECOGNIZE THE ASPECTS OF STEEL JOIST DESIGN
THAT THE PROGRAM ALGORITHMS DO NOT ADDRESS.

THE USER MUST EXPLICITLY UNDERSTAND THE ASSUMPTIONS OF THE
PROGRAM AND MUST INDEPENDENTLY VERIFY THE RESULTS.
                  ©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA JANUARY 2002
                                                              STEEL JOIST DESIGN
                                                                    Contents



Steel Joist Design
              1        General Design Information
                       Units                                                   1-1
                       Beams Designed as Steel Beams                           1-1
                             Section Requirements for Steel Joists             1-1
                             Material Property Requirements for
                                  Steel Joists                                 1-2
                             Other Requirements for Steel Joists               1-2
                             Frame Elements Designed by Default
                                  as Steel Joists                              1-2
                             Overwriting the Frame Design
                                  Procedure for a Steel Joist                  1-3
                       How the Program Optimizes Design Groups                 1-3
                       Analysis Sections and Design Sections                   1-4
                       Output Stations                                         1-6

              2        Steel Joist Design Process
                       Design Process                                          2-1

              3        Interactive Steel Joist Design
                       Member Identification                                   3-1
                       Section Information                                     3-2
                       Acceptable Sections List                                3-3
                       ReDefine                                                3-4
                       Temporary                                               3-4
                       Show Details                                            3-5

              4        Steel Joist Properties
                       General                                                 4-1
                       Joist Properties for Standard Design                    4-1


                                                                                   i
Steel Joist Design Manual


                                 Joist Properties for Envelope Design     4-3

                            5    Overwrites
                                 General                                  5-1
                                 Using the Steel Joist Overwrites Form    5-1
                                 Overwrites                               5-2

                            6    Design Load Combinations
                                 General                                  6-1

                            7    Design Checks for Standard Design
                                 Joist Span                               7-1
                                 Total Load Check                         7-1
                                 Live Load Check                          7-1
                                 Design of Joists When the Load is Not
                                       Uniform                            7-2

                            8    Design Checks for Envelope Design
                                 Moment Capacity                          8-1
                                 Shear Capacity                           8-1
                                 Live Load Deflection Check               8-1
                                 Maximum Equivalent Uniform Load Check    8-1

                            9    Data Plotted Directly on the Model
                                 Overview                                 9-1
                                 Labels Displayed on the Model            9-2
                                 Design Data                              9-2
                                 Design Ratios                            9-2

                            10   Output Details
                                 Summary of Steel Joist Output           10-1
                                 Steel Joist Detailed Output             10-2
                                 Steel Joist Design Check Messages       10-5




ii
                              ©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA JANUARY 2002
                                                                          STEEL JOIST DESIGN
                                                                      Technical Note 1
                                                General Design Information

This Technical Note presents some basic information and concepts that are
useful when performing steel joist design using this program.

Units
For steel joist design in this program, any set of consistent units can be used
for input. Typically, design codes are based on one specific set of units. The
documentation in the Steel Joist Design series of Technical Notes is pre-
sented in kip-inch-seconds units unless otherwise noted.

You can change the system of units at any time using the pull-down menu on
the Status Bar or pull-down menu on individual forms where available.

Note:
You can use any set of units in steel joist design and change the units "on the fly."

Beams Designed as Steel Joists
Section Requirements for Steel Joists
Only beams that are assigned joist sections can be designed as steel joists.
The joist sections can be selected from the built-in program joist section da-
tabase, or they can be user defined. The user-defined sections can be speci-
fied using the Define menu > Frame Sections command and clicking the
Add Steel Joist option.

Note that beam sections that are defined in Section Designer are always
treated as general sections. Thus, if you define a joist-type section in Section
Designer, the program will consider it as a general section, not a joist section,
and will not allow it to be designed as a steel joist.




Units                                                                        Technical Note 1 - 1
General Design Information                                                   Steel Joist Design


Note:
Beam sections defined in the section designer utility cannot be designed as steel joists.

Material Property Requirement for Steel Joists
If a beam is to be designed as a steel joist, the Type of Design associated
with the Material Property Data assigned to the beam must be Steel. Use the
Define menu > Material Properties > Modify/Show Materials command
to check your beams.

Other Requirements for Steel Joists
The line type associated with the line object that represents a steel joist must
be "Beam." In other words, the beam element must lie in a horizontal plane.
Right click on a line object to bring up the Line Information form to check the
Line Type.

For steel joists, the beam local 2-axis must be vertical. The Local axis 2 Angle
is displayed on the Assignments tab of the Line Information form.

The line object representing a steel joist should span from support to support.
Steel joists should not be modeled using multiple, adjacent line objects be-
tween supports for a single joist.

Frame Elements Designed by Default as Steel Joists
The program will design certain frame elements using the design procedures
documented in these Technical Notes by default. Those elements must meet
the following criteria:

    The beam must meet the section requirements described in the subsection
    entitled "Section Requirements for Steel Joists" in this Technical Note.

    The beam must meet the material property requirement described in the
    subsection entitled "Material Property Requirement for Steel Joists" in this
    Technical Note.

    The beam must meet the other requirements described in the subsection
    entitled "Other Requirements for Steel Joists" in this Technical Note.

    The beam must be assigned a steel joist section.




Technical Note 1 - 2                                            Beams Designed as Steel Joists
Steel Joist Design                                           General Design Information


    The beam must not frame continuously into a column or a brace. Both
    ends of the beam must be pinned for major axis bending (bending about
    the local 3-axis).

Overwriting the Frame Design Procedure for a Steel Joist
The design procedures possible for a beam that is assigned a steel joist sec-
tion design are:

    Steel joist design

    No design

All beam elements that meet the requirements described in the previous sub-
section entitled "Frame Elements Designed by Default as Steel Joists" are by
default designed using the steel joist design procedures.

Change the default design procedure used for a beam(s) by selecting the
beam(s) and clicking Design menu > Overwrite Frame Design Proce-
dure. This change is only successful if the design procedure assigned to an
element is valid for that element. For example, if you select two steel beams,
one an I-section and the other a joist section, and attempt to change the de-
sign procedure to Steel Joist Design, the change will be executed for the joist
section, but not for the I-section because it is not a valid section for the steel
joist design procedure.

How the Program Optimizes Design Groups
This section describes the process the program uses to select the optimum
section for a design group. In this description, note the distinction between
the term section, which refers to a joist section in an auto select section list,
and the term beam, which refers to a specific beam element in the design
group.

When considering design groups, the program first discards any beam in the
design group that is not assigned an auto select section list.

Next, the program looks at the auto select section list assigned to each beam
in the design group and creates a new list that contains the sections that are
common to all of the auto select section lists in the design group. The pro-




How the Program Optimizes Design Groups                            Technical Note 1 - 3
General Design Information                                                  Steel Joist Design


gram sorts this new common section list in ascending order, from smallest
section to largest section based on section weight.

Note:
When designing with design groups, the program attempts to quickly eliminate inade-
quate beams.

The program checks all beams in the design group for the first section (small-
est by weight) in the section list. If the section is adequate for all beams in
the design group, the optimum section has been identified. If the section is
not adequate for a beam, the next higher section in the section list is tried
until a section is found that is adequate for all beams in the design group.

If all sections in the section list are tried and none of them are adequate for
all of the beams in the design group, the program proceeds to design each
beam in the design group individually based on its own auto section list and
ignores the rest of the design group.

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 desig-
nated the current design section.

Tip:
It is important to understand the difference between analysis sections and design sec-
tions.

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 16K5
joist and then found in the design that a 16K3 joist worked. In that case, the
last used analysis section is the 16K5 and the current design section is the
16K3. Before you complete the design process, verify that the last used
analysis section and the current design section are the same. The Design
menu > Steel Joist Design > Verify Analysis vs Design Section com-
mand 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:




Technical Note 1 - 4                                     Analysis Sections and Design Sections
Steel Joist Design                                         General Design Information


    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 > Steel Joist 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.

    Deleting the static nonlinear analysis results also deletes the design re-
    sults for any load combination that includes static nonlinear forces. Typi-
    cally, static nonlinear analysis and design results are deleted when one of
    the following actions is taken:

         Use the Define menu > Frame Nonlinear Hinge Properties com-
         mand to redefine existing or define new hinges.

         Use the Define menu > Static Nonlinear/Pushover Cases com-
         mand 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 - 5
General Design Information                                     Steel Joist Design



Output Stations
Frame output stations are designated locations along a frame element. They
are used as locations to report output forces and to perform design, and as
plotting points used for graphic display of force diagrams. When force dia-
grams are plotted, exact forces are plotted at each output station and then
those points are connected by straight lines. Output stations occur at user-
specified locations and at point load locations along a beam. Designate the
output stations for a frame element using the Assign menu.




Technical Note 1 - 6                                             Output Stations
                          ©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA JANUARY 2002
                                                                      STEEL JOIST DESIGN
                                                                  Technical Note 2
                                             Steel Joist Design Process

This Technical Notes describes a basic steel joist design process using this
program. Although the exact steps you follow may vary, the basic design pro-
cess should be similar to that described herein. Other Technical Notes in the
Steel Joist Design series provide additional information.

Design Process
The following sequence describes a typical steel joist design process. Note
that although the sequence of steps you follow may vary, the basic process
probably will be essentially the same.

1. Create the building model.

2. Run the building analysis using the Analyze menu > Run Analysis
   command.

3. Assign steel joist overwrites, if needed, using the Design menu > Steel
   Joist Design > View/Revise Overwrites command. Note that you
   must select beams before using this command. Also note that default val-
   ues are provided for all steel joist design overwrites so it is unnecessary to
   define 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 Steel Joist Design Technical Note 5 Overwrites.

4. Designate design groups, if desired, using the Design menu > Steel
   Joist Design > Select Design Group command. Note that you must
   have already created some groups by selecting objects and clicking the
   Assign menu > Group Names command.

5. To use design load combinations other than the defaults created by the
   program for steel joist design, click the Design menu > Steel Joist De-
   sign > Select Design Combo command. Note that you must have al-




Design Process                                                           Technical Note 2 - 1
Steel Joist Design Process                                        Steel Joist Design


    ready created your own design combos by clicking the Define menu >
    Load Combinations command.

    See Steel Joist Design Technical Note 6 Design Load Combinations for
    more information.

6. Click the Design menu > Steel Joist Design > Start Design Without
   Similarity command to run the steel joist design.

7. Review the steel joist design results by doing one of the following:

    a. Click the Design menu > Steel Joist Design > Display Design
       Info command to display design input and output information on the
       model. See Steel Joist Design Technical Note 9 Data Plotted Directly on
       the Model for further discussion.

    b. Right click on a beam while the design results are displayed on it to
       enter the interactive design mode and interactively design the beam.
       Note that while you are in this mode, you can also view diagrams
       (load, moment, shear and deflection) and view design details on the
       screen. See Steel Joist Design Technical Note 3 Interactive Steel Joist
       Design for more information.

         If design results are not currently displayed (and the design has been
         run), click the Design menu > Steel Joist Design > Interactive
         Steel Joist Design command and then right click a beam to enter the
         interactive design mode for that beam.

    c. Use the File menu > Print Tables > Steel Joist Design command
       to print steel joist design data. If you select beams before using this
       command, data is printed only for the selected beams. See Steel Joist
       Technical Note 10 Output Details for more information.

    d. Use the Design menu > Steel Joist Design > Verify all Members
       Passed command to verify that no members are overstressed or oth-
       erwise unacceptable.

8. Use the Design menu > Steel Joist Design > Change Design Section
   command to change the steel joist design section properties for the se-
   lected joists.




Technical Note 2 - 2                                                Design Process
Steel Joist Design                                                    Steel Joist Design Process


9. Click the Design menu > Steel Joist Design > Start Design/Check of
   Structure command to rerun the steel joist design with the new section
   properties. Review the results using the procedures described in Step 8.

10. 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.

11. Click the Design menu > Steel Joist Design > Start Design/Check of
    Structure command to rerun the composite beam design with the new
    analysis results and new section properties. Review the results using the
    procedures described in Step 8.

12. Again use the Design menu > Steel Joist Design > Change Design
    Section command to change the steel joist design section properties for
    selected joists, if necessary.

13. Repeat Steps 11, 12 and 13 as many times as necessary.

Note:
Steel joist design in the program is an iterative process. Typically, the analysis and de-
sign will be rerun multiple times to complete a design.

14. Select all beams and click the Design menu > Steel Joist Design >
    Make Auto Select Section Null command. This removes any auto select
    section list assignments from the selected beams.

15. Rerun the building analysis using the Analyze menu > Run Analysis
    command. Note that the beam section properties used for the analysis are
    the last specified design section properties.

16. Click the Design menu > Steel Joist Design > Start Design/Check of
    Structure command to rerun the steel joist design with the new section
    properties. Review the results using the procedures described above.

17. Click the Design menu > Composite Beam 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.




Design Process                                                              Technical Note 2 - 3
Steel Joist Design Process                                          Steel Joist Design


18. Use the File menu > Print Tables > Steel Joist Design command to
    print selected steel design results if desired. See Steel Joist Technical Note
    10 Output Details for more information.

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 joist
section sizes and then run a design check using the forces obtained from that
analysis. Use the Design menu > Steel Joist Design > Verify Analysis vs
Design Section command to verify that the design sections are the same as
the analysis sections.




Technical Note 2 - 4                                                  Design Process
                           ©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA JANUARY 2002
                                                                       STEEL JOIST DESIGN
                                                                   Technical Note 3
                                          Interactive Steel Joist Design

Interactive steel joist design is a powerful feature that allows the user to re-
view the design results for any steel joist and interactively revise the design
assumptions and immediately review the revised results.

Note that a design must have been run for the interactive design mode to be
available. To run a design, click the Design menu > Steel Joist Design >
Start Design/Check of Structure command.

To enter the interactive design mode and interactively design the joist, right
click on a joist while the design results are displayed in the active window. If
design results are not displayed (and the design has been run), click the De-
sign menu > Steel Joist Design > Interactive Steel Joist Design com-
mand and then right click a joist.

The following sections describe the features that are included in the Interac-
tive Steel Joist Design and Review form.

Member Identification
Story ID
This is the story level ID associated with the steel joist.

Beam Label
This is the label of the line object to which the steel joist section is assigned.

Design Group
This is the name of the design group that the line object is assigned to if that
design group was considered in the design of the steel joist. If the line object
is part of a design group but the design group was not considered in the de-
sign, N/A is displayed. If the line object is not assigned to any design group,
"NONE" is displayed.

If a joist is redesigned as a result of a change made in the Interactive Steel
Joist Design and Review form, the design group is ignored and only the single



Member Identification                                                     Technical Note 3 - 1
Interactive Steel Joist Design                                            Steel Joist Design


beam is considered. Thus, as soon as you design a beam in the Interactive
Steel Joist Design and Review form, the Design Group box either displays N/A
or None.

Section Information
Auto Select List
This drop-down box displays the name of the auto select section list assigned
to the beam. If no auto select list has been assigned to the beam, NONE is
displayed. You can change this item to another auto select list or to NONE
while in the form and the design results will be updated immediately. If you
change this item to NONE, the design is performed for the Current De-
sign/Next Analysis section property.

Optimal
If an auto select section list is assigned to the beam, this box displays the op-
timal section as determined by joist weight. If no auto select list is assigned
to the beam, N/A is displayed for this item.

Last Analysis
This box displays the name of the section that was used for this beam in the
last analysis. Thus, the beam forces are based on a beam of this section
property. For the final design iteration, the Current Design/Next Analysis sec-
tion property and the Last Analysis section property should be the same.

Current Design/Next Analysis
This box displays the name of the current design section property. If the
beam is assigned an auto select list, the section displayed in this form initially
defaults to the optimal section.

Tip:
The section property displayed for the Current Design/Next Analysis item is used by the
program as the section property for the next analysis run.

If no auto select list has been assigned to the beam, the beam design is per-
formed for the section property specified in this box.

It is important to note that subsequent analyses use the section property
specified in this box for the next analysis section for the beam. Thus, the
forces and moments obtained in the next analysis are based on this joist size.




Technical Note 3 - 2                                                     Section Information
Steel Joist Design                                               Interactive Steel Joist Design


The Current Design/Next Analysis section property can be changed by clicking
the Sections button that is described later in this Technical Note.

Important note: Changes made to the Current Design/Next Analysis section
property are permanently saved (until you revise them again) if you click the
OK button to exit the Interactive Composite Beam Design and Review form. If
you exit the form by clicking the Cancel button, those changes are consid-
ered temporary and are not permanently saved.

Acceptable Sections List
The Acceptable Sections List includes the following information for each joist
section that is acceptable for all considered design load combinations.

    Joist section name

    Controlling design load combination

    Ratio type (flexural, shear or live load deflection)

    Controlling ratio

    Joist unit weight

Tip:
A single beam displayed in a red font in the Acceptable Sections List means that none of
the sections considered were acceptable.

Typically, the ratio displayed is the largest ratio obtained considering flexure,
shear and live load deflection.

If the beam is assigned an auto select list, many joist sections may be listed
in the Acceptable Sections List. If necessary, use the scroll bar to scroll
through the acceptable sections. The optimal section is initially highlighted in
the list.

If the joist is not assigned an auto select list, only one joist section will be
listed in the Acceptable Sections List. It is the same section as specified in the
Current Design/Next Analysis edit box.

At least one joist will always be shown in the Acceptable Sections List, even if
none of the joists considered are acceptable. When no joists are acceptable,



Acceptable Sections List                                                  Technical Note 3 - 3
Interactive Steel Joist Design                                   Steel Joist Design


the program displays the section with the smallest controlling ratio in a red
font. Thus, a single beam displayed in a red font in the Acceptable Sections
List means that none of the sections considered were acceptable.

ReDefine
Sections Button
Use the Sections button to change the Current Design/Next Analysis section
property. This button can designate a new section property whether the sec-
tion property is or is not displayed in the Acceptable Sections List.

When you click on the Sections button, the Select Sections form appears.
Assign any joist section property to the beam by clicking on the desired prop-
erty and clicking OK. Note that if an auto select list is assigned to the beam,
using the Sections button sets the auto select list assignment to NONE.

Overwrites Button
Click the overwrites button to access and make revisions to the steel joist
overwrites and then immediately see the new design results. Modifying some
overwrites in this mode and exiting both the Steel Joist Design Overwrites
form and the Interactive Steel Joist Design and Review form by clicking their
respective OK buttons permanently saves changes made to the overwrites.

Exiting the Steel Joist Design Overwrites form by clicking the OK button tem-
porarily saves changes. Subsequently exiting the Interactive Steel Joist De-
sign and Review form by clicking the Cancel button cancels the changes
made. Permanent saving of the overwrites does not occur until the OK but-
tons in both the Steel Joist Design Overwrites form and the Interactive Steel
Joist Design and Review form have been clicked.

Temporary
Combos Button
Click this button to access and make temporary revisions to the design load
combinations considered for the joist. This is useful for reviewing the results
for one particular load combination, for example. You can temporarily change
the considered design load combinations to be just the one you are interested
in and review the results.




Technical Note 3 - 4                                                     ReDefine
Steel Joist Design                                       Interactive Steel Joist Design


The changes made to the considered design load combinations using the
combos button are temporary. They are not saved when you exit the Interac-
tive Steel Joist Design and Review form, whether you click OK or Cancel to
exit it.

Show Details
Diagrams Button
Clicking the Diagrams button displays a form with the following four types of
diagrams for the beam.

    Applied loads

    Shear

    Moment

    Deflection

The diagrams are plotted for specific design load combinations specified in the
form by the user.

Details Button
Clicking the Details button displays design details for the joist. The informa-
tion displayed is similar to the detailed output that can be printed using the
File menu > Print Tables > Steel Joist Design command. See Steel Joist
Design Technical Note 10 Output Details for more information.




Show Details                                                      Technical Note 3 - 5
                         ©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA JANUARY 2002
                                                                     STEEL JOIST DESIGN
                                                                 Technical Note 4
                                                     Steel Joist Properties

This Technical Note provides an overview of steel joist properties, including
their design capacities.

General
Steel joist properties are defined using the Define menu > Frame Sections
command. Use this command to import joist properties from the joist section
database file named joists.pro that is provided with the program, or to define
your own joist sections. The joist sections available in the database include
the K-Series, KCS-Series, LH-Series and DLH-Series as defined by the Steel
Joist Institute (SJI).

Two types of joist design capacities are considered by the program: Standard
and Envelope design. Standard design is based on specified total uniform load
capacities and live uniform load capacities for a range of spans. Envelope de-
sign is based on specified moment and shear capacities and a specified mo-
ment of inertia that is used to calculate deflection.

The K-Series, LH-Series and DLH-Series joists use the Standard design ca-
pacities. The KCS-Series joists use the Envelope design capacities. User
specified joists can use either Standard design or Envelope design. Each of
the design types is described in more detail later in this technical note.

Joist Properties for Standard Design
Figure 1 shows the Joist Section Properties form for a joist using Standard
design. For Standard design, a series of joist spans is specified along with a
total load capacity for each span and a live load capacity that produces an
L/360 deflection for each span.

In addition, a moment of inertia is provided for each span. This moment of
inertia is only used when reporting the joist deflection in Interactive Steel




General                                                                 Technical Note 4 - 1
Steel Joist Properties                                                      Steel Joist Design




                       Figure 1: Joist Properties - Standard Design

Joist Design and Review (see Steel Joist Design Technical Note 3 Interactive
Steel Joist Design); it is not actually used in the design of the joist.

The joist depth item is specified but is not currently used in the design.

The joist unit weight is used both to calculate an area for the section that is in
the analysis, and to optimize the design when auto select section lists are
used. The optimum joist is the lightest joist that passes all of the design
checks.

The Analysis I33 item is used as the moment of inertia for the joist in the
analysis.




Technical Note 4 - 2                                      Joist Properties for Standard Design
Steel Joist Design                                                  Steel Joist Properties



Joist Properties for Envelope Design
Figure 2 shows a the Joist Section Properties form for a joist using Envelope
design. For Envelope design a moment and shear capacity are specified along
with a minimum and maximum span for which the joist will be designed.




                     Figure 2: Joist Properties - Envelope Design

The joist depth item is specified but is not currently used in the design.

The joist unit weight is used both to calculate an area for the section that is in
the analysis, and to optimize the lightest joist that passes all of the design
checks.

The Analysis I33 item is used both as the moment of inertia for the joist in
the analysis and also to calculate the joist deflection, both for design checks
and when the joist deflection is reported in Interactive Steel Joist Design and
Review (see Steel Joist Design Technical Note 3 Interactive Steel Joist De-
sign).


Joist Properties for Envelope Design                                 Technical Note 4 - 3
                          ©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA JANUARY 2002
                                                                      STEEL JOIST DESIGN
                                                                  Technical Note 5
                                                                         Overwrites

This Technical Note provides instructions on how to use the Steel Joist Design
Overwrites form and describes each overwrite.

General
The steel joist design overwrites are basic assignments that apply only to
those steel joists to which they are assigned. After selecting one or more steel
joists, use the Design menu > Steel Joist Design > View/Revise Over-
writes command to access the Steel Joist Design Overwrites form where you
can view and revise the steel joist design overwrites.

Default values are provided for all steel joist overwrite items. Thus, it is not
required that you specify or change any of the overwrites. However, at least
review the default values for the overwrite items to make sure they are ac-
ceptable. 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.

Using the Steel Joist Overwrites Form
After selecting one or more steel joist, use the Design menu > Steel Joist
Design > View/Revise Overwrites command to access the Steel Joist De-
sign Overwrites form.

The steel joist overwrites are displayed with a column of check boxes and a
two-column spreadsheet. The left column in the spreadsheet contains the
name of the overwrite item. The right column in the spreadsheet contains the
overwrite value.

Initially, the check boxes are all unchecked and all of the cells in the spread-
sheet have a gray background to indicate they are inactive and that the items
in the cells currently cannot be changed. The names of the overwrite items in
the first column of the spreadsheet are visible. The values of the overwrite



General                                                                  Technical Note 5 - 1
Overwrites                                                         Steel Joist Design


items in the second column of the spreadsheet are visible if only one joist was
selected before the Steel Joist design Overwrites form was accessed. If multi-
ple joists were selected, no values show for the overwrite items in the second
column of the spreadsheet.

After selecting one or multiple joists, check the box to the left of an overwrite
item to change it. Then left click in either column of the spread sheet to acti-
vate a drop-down box or to highlight the contents of the cell in the right col-
umn of the spreadsheet. If the drop-down box appears, select a value from
the box. If the cell contents becomes highlighted, type in the desired value.
The overwrite will reflect the change. You cannot change the values in the
drop-down boxes.

When you check a check box or left click in one of the columns in the spread-
sheet, a short description of the item in that row displays in the large text box
just below the list of items. This description helps you recall the purpose of
the overwrite item without referring to the manual.

When changes to the steel joist overwrites have been made, 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 joist(s). 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
will be ignored and the form will be closed.

Overwrites
For purposes of explanation in this Technical Note, the overwrite items are
presented in tables. The column headings in these tables are described as
follows.

    Item: The name of the overwrite item as it appears in the cells at the left
    side of the Steel Joist Design Overwrites form.

    Possible Values: The possible values for the associated overwrite item.

    Default Value: The built-in default value that the program assumes for
    the associated overwrite item.

    Description: A description of the associated overwrite item.



Technical Note 5 - 2                                                      Overwrites
Steel Joist Design                                                                     Overwrites




Table 1: Steel Joist Overwrites

                       Possible        Default
      Item              Values         Value                       Description

Current design       Any defined     The current    The current design section for the joist.
section              joist section   joist design
                                        section

LL deflection             >0             360        Deflection limitation for live load. Input-
limit (L/)                                          ting 360 means that the limit is L/360
                                                    where L is the length of the joist.

Reduced live           Program        Program       Reducible live load is multiplied by this
load factor          calculated or   calculated     factor to obtain the reduced live load. If
                     user-defined                   zero is selected, the program calcu-
                                                    lated valued is used.
Ignore                 Yes, No           No         This item is Yes if story level similarity
similarity                                          (to a master story level) is to be ignored
                                                    when designing the joist.




Overwrites                                                                    Technical Note 5 - 3
                             ©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA JANUARY 2002
                                                                         STEEL JOIST DESIGN
                                                                     Technical Note 6
                                               Design Load Combinations

This Technical Note described the default design load combinations for steel
joist design in the program.

General
Two default design load combinations created by the program for steel joist
design are:

          Σ(DL) + Σ(SDL)                                                               Eqn. 1

          Σ(DL) + Σ(SDL) + Σ(LL) + Σ(RLL)                                              Eqn. 2

where

          Σ(DL)    = Sum of all dead load applied to the joist.

          Σ(SDL) = Sum of all superimposed dead load applied to the joist.

          Σ(LL)    = Sum of all live load applied to the joist.

          Σ(RLL)   = Sum of all reducible live load applied to the joist.

You can replace or supplement these default design load combinations with
your own design load combinations, if desired.




General                                                                     Technical Note 6 - 1
                           ©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA JANUARY 2002
                                                                       STEEL JOIST DESIGN
                                                                   Technical Note 7
                              Design Checks for Standard Design

This Technical Note describes the design checks performed by the program
for Standard joist design.

Joist Span
The joist span used to determine the capacity of K-Series and User joists is
the full center-of-support to center-of-support span.

For LH-Series and DLH-Series joists, the joist span is taken as the full center-
of-support to center-of-support span minus 8 inches.

Total Load Check
For the total load check, the program calculates the ratio of the maximum
total uniform load acting on the joist divided by the total uniform load capac-
ity of the joist. This ratio is reported in the output.

Live Load Check
For the live load check, the program first calculates the uniform live load ca-
pacity using Equation 1.

         LL Capacity = L/360 Capacity *(360 / LL Defl Limit)                         Eqn. 1

where,

         LL Capacity     = Maximum uniform live load capacity

         L/360 Capacity = Uniform live load capacity specified for the joist span
                          in the joist section properties

         LL Defl Limit   = Live load deflection limit specified in the overwrites




Joist Span                                                                Technical Note 7 - 1
Design Checks for Standard Design                                         Steel Joist Design


The program then calculates the ratio of the maximum uniform live load act-
ing on the joist divided by the uniform live load capacity of the joist. This ratio
is reported in the output.

Design of Joists When the Load is Not Uniform
For Standard design, the program checks if the applied load is uniform. If the
load is not uniform, the design section is displayed with SP appended to its
name.

The program uses the following method to determine if the load applied in a
particular design load combination is uniform.

1. Find the maximum moment in the joist.

2. Calculate the uniform load that produces this maximum moment.

3. Calculate the moment cause by the uniform load calculated in step 2 at
   each design output station along the joist.

4. Compare the actual moments obtained from the analysis at each design
   output station with the moments calculated in step 3. If any of the mo-
   ments differ by more than 5%, the load is reported as not uniform.

When the load is not uniform, the program uses an equivalent uniform load to
determine the design ratios. The equivalent uniform load is the one calculated
in step 2 above, and is equal to 8 * Mmax / Span2.




Technical Note 7 - 2                           Design of Joists When the Load is Not Uniform
                          ©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA JANUARY 2002
                                                                      STEEL JOIST DESIGN
                                                                  Technical Note 8
                             Design Checks for Envelope Design

This Technical Note describes the design checks performed by the program
for Envelope joist design.

Moment Capacity
For the moment capacity check, the program calculates the ratio of the
maximum moment anywhere in the joist divided by the moment capacity of
the joist. This ratio is reported in the output.

Shear Capacity
For the shear capacity check, the program calculates the ratio of the maxi-
mum shear in the joist divided by the shear capacity of the joist. This ratio is
reported in the output.

The program also checks that the largest point load anywhere on the joist
does not exceed the shear capacity of the joist.

Live Load Deflection Check
For the live load deflection check, the program calculates the ratio of the ac-
tual maximum live load deflection, calculated using the Analysis I33, divided
by the live load deflection limit specified in the steel joist overwrites.

Maximum Equivalent Uniform Load Check
For Envelope design, the program checks that the maximum equivalent uni-
form load on the joist does not exceed 550 plf. The maximum equivalent
uniform load is equal to 8 * Mmax / Span2, where Mmax is the maximum
moment and Span is the joist span.




Moment Capacity                                                          Technical Note 8 - 1
                             ©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA JANUARY 2002
                                                                         STEEL JOIST DESIGN
                                                                     Technical Note 9
                                   Data Plotted Directly on the Model

This Technical Note describes the steel joist design input and output data that
can be plotted directly on the model.

Overview
Use the Design menu > Steel Joist Design > Display Design Info com-
mand to display on-screen output plotted directly on the model. If desired,
the screen graphics can then be printed using the File menu > Print
Graphics command.

The on-screen display data is organized into three data groups, as follows.

    Labels

    Design Data

    Design Ratios

Each of those data groups is described in more detail later in this Technical
Note. It is important to note that items from different data groups cannot be
displayed simultaneously.

Tip:
The colors related to the joist ratios can be modified by clicking the Options menu >
Colors > Output command.

When design information is displayed directly on the model, the frame ele-
ments are displayed in a color that indicates the value of their controlling ra-
tio. (Note that this controlling ratio may be a flexural, shear or live load de-
flection ratio.) The colors associated with various ranges of ratios are speci-
fied in the Steel Ratios area of the Assign Output Colors form, which is ac-
cessed using the Options menu > Colors > Output command.




Overview                                                                    Technical Note 9 - 1
Data Plotted Directly on the Model                                            Steel Joist Design



Labels Displayed on the Model
Beam labels and associated beam design group labels can be displayed on the
model. A beam label is the label that is assigned to the line object that repre-
sents the steel joist.

Tip:
Long labels may not display or print properly (fully).

If a beam has been assigned to a group that has been designated as a steel
joist design group, the group name for the beam will be displayed when re-
quested. If a beam is not part of a steel joist design group, no group name
will be displayed for that beam. Note that you can assign steel joist design
groups by clicking the Design menu > Steel Joist Design > Select Design
Group command.

Tip:
The design data and ratios output that is plotted directly on the model is also available in
text form in the printed output, which is described in Technical Note Output Details.

Design Data
The following design data can be displayed on the model:

    Joist section (e.g., 16K3)

    Joist end reactions

One or both of these items can be displayed at the same time.

Design Ratios
The following design data can be displayed on the model:

    Controlling ratio

    Controlling ratio type

The controlling ratio is the maximum design ratio obtained for the joist. The
controlling ratio type is either flexure, shear or LL Deflection, indicating the
type of design check that yielded the maximum design ratio.




Technical Note 9 - 2                                              Labels Displayed on the Model
                                   ©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA JANUARY 2002
                                                                               STEEL JOIST DESIGN
                                                                         Technical Note 10
                                                                            Output Details

This Technical Note describes the steel joist design output that can be printed
to a printer or to a text file. It also documents the design check messages, for
example, CHK#2, that indicate the program is unable to design a particular
joist. All the output data documented in this Technical Note, except for the
summary output data, also appears when the Details button in the Show
Details area of the Interactive Steel Joist Design and Review form is clicked.
See Steel Joist Design Technical Note 3 Interactive Steel Joist Design for
more information.

The program provides the output data in a series of tables. The heading or
title for each piece of output data and a description of the data are provided
in the tables in this Technical Note.

Summary of Steel Joist Output
This output is printed when you click the File menu > Print Tables > Steel
Joist Design command and check the Output Summary checkbox on the re-
sulting form. Similar output also appears on screen if you click the Details
button in the Show Details area of the Interactive Composite Beam Design
and Review form. See Steel Joist Design Technical Note 3 Interactive Steel
Joist Design for more details on the interactive design.

Table 1 Summary of Steel Joist Output
OUTPUT ITEM                     DESCRIPTION
Story Level                     Story level associated with the joist.

Beam Label                      Label associated with the line object that represents the joist. A
                                typical label beam would appear as "B23." Do not confuse this
                                with the Design Section Label, which might be identified as
                                "16K3."




Summary of Steel Joist Output                                                    Technical Note 10 - 1
Output Details                                                               Steel Joist Design



Table 1 Summary of Steel Joist Output
OUTPUT ITEM              DESCRIPTION
Design Section           The joist section selected as a result of the design process, for
                         example, 16K3.

Maximum Ratio            The maximum design ratio for the joist. See Steel Joist Design
                         Technical Note 7 Design Checks for Standard Design and Steel
                         Joist Design Technical Note 8 Design Checks for Envelope De-
                         sign for a description of how the ratio is calculated.

Ratio Type               This is either flexure, shear or LL Deflection, indicating the de-
                         sign check that produced the Maximum Ratio.




Steel Joist Detailed Output
This output is printed when you click the File menu > Print Tables > Steel
Joist Design command and check the Detailed Output checkbox on the re-
sulting form. Similar output also appears on screen if you click the Details
button in the Show Details area of the Interactive Steel Joist Design and Re-
view form. See Steel Joist Design Technical Note 3 Interactive Steel Joist De-
sign for more details on the interactive design.

Table 2 Steel Joist Detailed Output
OUTPUT ITEM              DESCRIPTION
Basic Beam Information
Joist                    The joist section selected as a result of the design process, for
                         example, 16K3.

Beam Label               Label associated with the line object that represents the joist. A
                         typical label beam would appear as "B23." Do not confuse this
                         with the Design Section Label, which might be identified as
                         "16K3."

Story                    Story level associated with the joist.

Length                   Length of the joist.




Technical Note 10 - 2                                                Steel Joist Detailed Output
Steel Joist Design                                                                       Output Details



Table 2 Steel Joist Detailed Output
OUTPUT ITEM                    DESCRIPTION
Loc X                          Global X coordinate of the center of the joist.

Loc Y                          Global Y coordinate of the center of the joist.

Group                          Name of the design group (if any) to which the beam has been
                               assigned.

Joist Overwrite Data
LL Deflection Limit            The live load deflection limit specified for the joist.

Ignore Similarity              This item is Yes if story level similarity (to a master story level)
                               is to be ignored when designing the joist.

RLLF                           A reducible live load is multiplied by this factor to obtain the re-
                               duced live load.

Joist Design Results - Standard Design
Analysis section               The joist section used in the last analysis of the structure.

Design section                 The joist section selected as a result of the design process.

Span used to select            The joist span that the program used to select the joist Uniform
capacities                     TL Capacity and Uniform LL Capacity.

Load type                      This is either Uniform or Not Uniform, indicating the type of load
                               assumed by the program. See Steel Joist Design Technical
                               Note 7 Design Checks for Standard Design for a description of
                               how the program determines if a load is uniform.

Controlling Ratio              The controlling design ratio for the joist. It is the larger of the
                               Uniform TL Ratio and the Uniform LL Ratio.

Uniform TL Combo               The design load combination that produces the largest Uniform
                               TL (total load) Ratio.

Equivalent Uniform TL          The equivalent uniform total load acting on the joist. See Steel
                               Joist Design Technical Note 7 Design Checks for Standard De-
                               sign for a description of equivalent uniform total load.

Uniform TL Capacity            The specified uniform total load capacity of the joist.



Table 2 Steel Joist Detailed Output                                               Technical Note 10 - 3
Output Details                                                                Steel Joist Design



Table 2 Steel Joist Detailed Output
OUTPUT ITEM             DESCRIPTION
Uniform TL Ratio        The ratio obtained by dividing the Equivalent Uniform TL by the
                        Uniform TL Capacity.

Uniform LL Combo        The design load combination that produces the largest Uniform
                        LL (live load) Ratio.

Equivalent Uniform LL   The equivalent uniform live load acting on the joist.

Uniform LL Capacity     The specified uniform live load capacity for an L/360 deflection
                        of the joist.

Uniform LL Ratio        The ratio obtained by dividing the Equivalent Uniform LL by the
                        Uniform LL Capacity and then multiplying by a factor to account
                        for the possibility that the specified live load deflection limit may
                        be different from L/360. See Steel Joist Design Technical Note
                        7 Design Checks for Standard Design for a description of how
                        this ratio is calculated.

Joist Design Results - Envelope Design
Analysis section        The joist section used in the last analysis of the structure.

Design section          The joist section selected as a result of the design process.

Load type               This is either Uniform or Not Uniform indicating the type of load
                        assumed by the program. See Steel Joist Design Technical
                        Note 7 Design Checks for Standard Design for a description of
                        how the program determines if a load is uniform.

Equivalent uniform      The equivalent uniform total load acting on the joist. See Steel
total load              Joist Design Technical Note 8 Design Checks for Envelope De-
                        sign for a description of how this is calculated.

Minimum joist length    The minimum span for which the joist design section will be
                        designed by the program.

Maximum joist length    The maximum span for which the joist design section will be
                        designed by the program.

Controlling Ratio       The controlling design ratio for the joist. It is the larger of the
                        Moment Ratio, Shear Ratio and the LL Deflection Ratio.




Technical Note 10 - 4                                         Table 2 Steel Joist Detailed Output
Steel Joist Design                                                                   Output Details



Table 2 Steel Joist Detailed Output
OUTPUT ITEM                 DESCRIPTION
Maximum Moment              The design load combination that produces the Maximum Mo-
Combo                       ment.

Maximum Moment              The maximum moment acting on the joist.

Moment Capacity             The specified moment capacity of the joist.

Moment Ratio                The ratio obtained by dividing the Maximum Moment by the
                            Moment Capacity.

Maximum Shear               The design load combination that produces the Maximum
Combo                       Shear.

Maximum Shear               The maximum shear acting on the joist.

Shear Capacity              The specified shear capacity of the joist.

Shear Ratio                 The ratio obtained by dividing the Maximum Shear by the Shear
                            Capacity.

LL Deflection Combo         The design load combination that produces the Maximum LL
                            Deflection.

Maximum LL Deflec-          The maximum live load deflection for the joist.
tion

LL Deflection Limit         The specified live load deflection limit for the joist in Length
                            units.

LL Deflection Ratio         The ratio obtained by dividing the Maximum LL Deflection by
                            the LL Deflection Limit.




Steel Joist Design Check Messages
This output is displayed on the model and in the printed output when the pro-
gram is unable to design a particular joist. The check messages, such as
CHK#2, are a "shorthand" way of indicating the design problem.




Steel Joist Design Check Messages                                             Technical Note 10 - 5
Output Details                                                                Steel Joist Design


In the printed Steel Joist Detailed Output and the output obtained from the
Interactive Steel Joist Design and Review form, descriptive messages are pro-
vided along with the shorthand messages. In the printed Summary of Steel
Joist Output and for display on the model, only the shorthand messages are
provided.

Table 3 shows that descriptive messages that correspond to the shorthand
check messages.

Table 3 Steel Joist Design Check Messages
OUTPUT ITEM             DESCRIPTION
CHK# 1                  Error: No section in the auto select list is adequate for this joist.

CHK# 2                  Error: The element is not designed because it is not a joist sec-
                        tion.

CHK# 3                  Error: This joist is not designed because there is negative mo-
                        ment.

CHK# 4                  Error: This joist is not designed because the equivalent uniform
                        load exceeds 550 plf.

CHK# 5                  Error: This joist is not designed because a single concentrated
                        load exceeds the shear capacity.

CHK# 6                  Error: This joist is not designed because no load data exists for
                        spans this short.

CHK# 7                  Error: This joist is not designed because no load data exists for
                        spans this long.




Technical Note 10 - 6                                 Table 3 Steel Joist Design Check Messages

				
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