Moment Amplification Factor for P-δ Effect of Steel Beam-Column

The American Institute of Steel Construction load and resistance factor design (AISC-LRFD) Specification states that second-order effects should be considered in the design of frames; however, most designers are experienced only in first-order analysis. To accomplish the second-order design requirement, the AISC-LRFD Specification provides an approximate method to account for the second-order effect bases on first-order analysis, where moment amplification factors B₁ and B₂ are introduced to account for the P-δ effect (member instability) and PΔ effect (frame instability), respectively. However, the B₁ factor of the AISC-LRFD Specification may vary greatly from the exact solution, especially when the member is under a high axial load. In this paper, a new moment amplification factor ${\mathit{B}}_{\mathit{1}}^{\mathit{*}}$ is proposed for calculating the P-δ effect in the design of steel beam-columns. Parametric studies were performed to examine the accuracy of the proposed moment amplification factor and to compare it with that from theoretical analysis and from current design specification. It was found that the proposed method is simpler and more accurate than that given in the current design specification.