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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

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)

- 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

if shape has compact sections

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