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									REVIEW OF STEEL DESIGN
 KNOWLEDGE BASE REQUIRED:

 STRENGTH OF MATERIALS
 TIMBER DESIGN
 SOIL MECHANICS
 STEEL DESIGN
REVIEW OF STEEL DESIGN
 BASIC STEEL DESIGN REVIEW:

Review of AISC Construction Manual (cont):

Compact vs. Non- Compact
Compact Beam are rolled beam that can achieve
the plastic moment.

     Stress Distribution of I Beam




      section    non- compact   compact
  REVIEW OF STEEL DESIGN
    BASIC STEEL DESIGN REVIEW:

Review of AISC Construction Manual (cont):

Compact Sections-
•are symmetrical about the y-y axis
•webs/flanges must have certain width-thickness ratios
 (Spec Section - Table B5.1,P.5-36)
•compression flange must be adequately braced
 against lateral buckling
•When the theoretical yield stress F’y is equal to or
 exceeded by the yielding stress of 65ksi than the
 section is compact.
  REVIEW OF STEEL DESIGN
    BASIC STEEL DESIGN REVIEW:
Design Procedure for Bending(using Sx)
1. Determine the Maximum Bending Moment

2. Compute the Required Section Modulus based
   on allowable stresses Fb=.66Fy (compact)
   [equat. F1-1,Chapt. F1.1] or Fb=.60 Fy
  (for non compact)[equat. F1-5,Chapt. F1.2]

3. Enter the ASD selection table and find the
   nearest tabulated value of Sx. The lightest weight
   and the most economical section that will serve for
   the yield strength stated is in bold face, and should
   be selected adjacent to or above the required Sx.

4. Check F’y column to be sure of compact section.

5. Check the lc & lu to make sure of adequate
   bracing.
  REVIEW OF STEEL DESIGN
    BASIC STEEL DESIGN REVIEW:



Note:For Members with Compact or Non-compact
    sections.

• Recall lc is the max. unbraced length in feet of the
  compression flange at which the allowable bending
  is taken at 0.66 Fy

• Recall lu is the max. unbraced length in feet of the
  compression flange for which allowable bending
  stress may be taken at 0.60 Fy when Cb=1
  REVIEW OF STEEL DESIGN
    BASIC STEEL DESIGN REVIEW:
Recall l, lc, and lu
if l is the given length between lateral supports
then,
• lc>l use Fb=.66Fy (assuming compact section)
• lu>l>lc use Fb=.60Fy
• l>lu use the charts of allowable moments in beams
  (p.2-146 to 2-212) where Cb=1

Note: Cb is the bending coefficient dependent upon
moment gradient (F1.3)
                       M1          M1 2
     Cb  1.75  1.05(    )  0.3(    )
                       M2          M2
 Cb=1
 •when the bending moment at any point within
  an unbraced length is larger than that at both
  ends of this length
 •when frames are braced against joint translation.
 •when considering a conservative value for cantilever
  REVIEW OF STEEL DESIGN
    BASIC STEEL DESIGN REVIEW:

Given:
Select a beam of Fy=36ksi steel subjected to a
bending moment of 125 kip-ft., having its compression
flange braced at 6 ft. intervals.
Solution:
Assume compact section, Fb=0.66Fy=23.8ksi

1. Maximum Bending Moment Given in Problem
2. Sx(reqd)=M/Fb=(125x12)/23.8=63 cu.in.

3. Nearest Tabulated Value
W16x40 64.7
W12x50 64.7

Since W16x40 is bold face, it is the lightest
suitable section that will serve for that yield strength.
  REVIEW OF STEEL DESIGN
    BASIC STEEL DESIGN REVIEW:

Given:
Select a beam of Fy=36ksi steel subjected to a
bending moment of 125 kip-ft., having its compression
flange braced at 6 ft. intervals.

Solution contd:

4. A check of the F’y column shows a dash, indicating
   that F’y is greater than 65 ksi. Therefore, the shape
   is compact.

5. From the table, Lc=7.4 ft. >6.0 ft. so the bracing is
   adequate and the assumed allowable stress of .66Fy
   is correct. Use W16x40
  REVIEW OF STEEL DESIGN
    BASIC STEEL DESIGN REVIEW:
    Recall: Mr is the beam resisting moment
       Fb S x
 MR          kip  ft
        12
 where
 Fb  .66 Fy         if shape has compact sections

 Fb  Fy [0.79  0.002(b f / 2t f ) Fy
             if shape has non compact flanges

Design Procedure for Bending(using Mr)

1. Enter the ASD selection table and find the
   nearest tabulated value of Mr. The lightest weight
   and the most economical section that will serve for
   the yield strength stated is in bold face, and should
   be selected adjacent to or above the required Mr.
  REVIEW OF STEEL DESIGN
    BASIC STEEL DESIGN REVIEW:

2. Check F’y column to be sure of compact section.
3. Check the lc & lu to make sure of adequate
   bracing.
4. Remember Mr is only valid for l<lc

Given:
Select a beam of Fy=36ksi steel subjected to a
bending moment of 125 kip-ft., having its compression
flange braced at 6 ft. intervals.

Solution:
Assume compact section, Fb=0.66Fy=23.8ksi

1. Enter Bending Moment Given in Problem
    Nearest Tabulated Value
    W16x40 128 k-ft
    W12x50 128 k-ft

 Since W16x40 is bold face, it is the lightest
 suitable section that will serve for that yield strength.
  REVIEW OF STEEL DESIGN
    BASIC STEEL DESIGN REVIEW:

Given:
Select a beam of Fy=36ksi steel subjected to a
bending moment of 125 kip-ft., having its compression
flange braced at 6 ft. intervals.

3. Check F’y column to be sure of compact section.
   OK the same as before
4. Check the lc & lu to make sure of adequate
   bracing.
   Lc=7.4ft > 6.0ft therefore Mr is valid
   Use W16x40

								
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