Combined Bending and Compression

 

Bending and Axial Compression  (NDS section 3.9.2)

beam-columns are common

 

 

Zahn's Formula Considers/Combines

1. column buckling
2. lateral torsional stability
3. beam-column interaction

 

 

Amplification Factor

• bending + axial compression more critical than bending + axial tension
• P-Δ effect  (second-order effect)

source

• bending moment causes deflection 
• axial load causes further deflection due to curved shape
• but mechanics of materials does not take this into account
• bending stress is amplified in interaction formula

 

 

General Interaction Formula  (NDS section 15.4)

axial compression biaxial bending P-Δ effect eccentric bending additional P-Δ effect