1. Column Theory - Column Strength Curve

2. Example I OK – Column is Stable
A W12x50 is used as a column to support a compressive load of 145 kips. The length is 20 ft and the ends are pinned. Without regard to LRFD or ASD investigate the stability of the column
For a W12x50
OK – Column is Stable

3. Example I NG – Column is Unstable
A W12x50 is used as a column to support a compressive load of 145 kips. The length is 20 ft the bottom is fixed and the top is free. Without regard to LRFD or ASD investigate the stability of the column
For a W12x50
NG – Column is Unstable

4. AISC Requirements CHAPTER E pp 16.1-32 Nominal Compressive Strength
AISC Eqtn E3-1

5. AISC Requirements
LRFD

6. AISC Requirements
ASD

7. AISC Requirements
ASD – Allowable Stress

8. To compute Fcr – ELASTIC BUCKLING
Recall Assumptions

9. Column is perfectly straight The load is axial, with no eccentricity
Assumptions
Column is perfectly straight
The load is axial, with no eccentricity
The column is pinned at both ends

10. To compute Fcr – ELASTIC BUCKLING
Accounts for Imperfections

11. To compute Fcr – INELASTIC BUCKLING

12. Design Strength

13. Alternatively
Inelastic Buckling

14. In Summary

15. Example
A W14x74 of A992 steel has a length of 20 feet and pinned ends. Compute the design strength for LRFD and the allowable compressive strength for ASD
Slenderness Ratio

16. Example

17. Example
LRFD
ASD