Experimental investigation of the P-Δ effect of low rise unbraced steel frames

Abstract

In this study, the influences of the P-Δ effect on the behavior of low rise unbraced steel frames and the validity of factor B2, which is suggested by KBC 2008 (draft) to consider the P-Δ effect, were evaluated using the experimental approach. Seven specimens, one story-one bay unbraced steel frames, were tested under static loading conditions. The main parameters of the tests were the stiffness ratio of the column to the beam, and the axial load ratio. As revealed by the experimental research that was conducted, the axial load and the decrement of frame stiffness are the main factors that govern the P-Δ effect and that influence the P-Δ effect on the frame behavior. The story stiffness of the frame, which is related to factor B2, was dramatically decreased when the nonlinear behavior started. Factor B2 was compared with the moment amplification factor obtained in the test that had been conducted, and it was found that factor B2, which is based on the linear elastic theory, does not properly estimate the P-Δ effect of an unbraced frame when its assumptions are not satisfied. Thus, careful consideration is needed to apply factor B2 if the design is made using the inelastic part of the material.