1. Design of Beams - Limit States
Flexure
Elastic
Plastic
Stability (buckling)
Shear
Deflection

2. Nominal Flexural Strength – Compact Shapes

3. Nominal Flexural Strength – NON-Compact Shapes
FLB

4. Design for Shear Large concentrated loads placed near beam supports
Rigid connection of beams and columns with webs on the same plane
Notched or coped beams
Heavily loaded short beams
Thin webs in girders

5. Design for Shear V: Vertical shear at the section under consideration
Q: First moment about of neutral axis of area of the cross section between point of interest and top or bottom of section (depends on y)
I: Moment of inertia of section
b: width of section at point of interest

6. Web fails before flanges
Design for Shear
Small width b
d/b=2 Error ~3%
d/b=1 Error ~12%
d/b=1/4 Error 100%
Web fails before flanges
Average Shear Stress
Nominal Strength if no buckling:

7. Design for Shear h/tw Failure of Web due to Shear: Yielding
Inelastic Buckling
Elastic Buckling
h/tw>260 Stiffeners are required
Appendix F2

8. Design for Shear AISC Specs G pp 16.1-64
Shear Strength must be sufficient to satisfy
LRFD
resistance factor for shear=0.9
maximum shear based on the controlling combination for factored loads
nominal shear strength
depends on failure mode
ASD
maximum shear based on the controlling combination for service loads
Safety factor

9. AISC Spec requirements for Shear
Cv depends on whether the limit state is web yielding, web inelastic buckling or web elastic buckling

10. AISC Spec requirements for Shear
Special Case for Hot Rolled I shapes with
Most W shapes with

11. AISC Spec requirements for Shear Chapter G
All other doubly and singly symmetric shapes except round HSS

12. DEFLECTIONS AISC Specs Chapter L
Serviceability Limit State
Limiting Value
Deflections due to Service Loads
<
Governing Building Code, IBC etc
Use deflection formulas in AISC Part 3 Or standard analytical or numerical methods
Calculate due to UNFACTORED (service) loads

13. Shear is rarely a problem in rolled steel beams usual practice
Design
Shear is rarely a problem in rolled steel beams
usual practice
Design for Flexure and Check for Shear and Deflections Or
Design for Deflections and Check for Flexure and Shear

14. Design Compute Required Moment Strength Mu or Ma
Weight of Beam can be assumed and verified or ignored and checked after member is selected
Select shape that satisfies strength requirements
Assume shape, compute strength, compare with required, revise if necessary or
Use beam design aids in Part 3 of the Manual
Check Shear and deflections

15. HOMEWORK
5.2-3
5.4-1
5.5-3
5.5-5
5.6-2
5.8-2