BUCKLING STRENGTH OF COLUMNS IN LOW-RISE MULTI-SPAN FRAMES EVALUATED BY THE STABILITY INDEX

Abstract

The objective of this study was to investigate the validity of the effective length factors for low-rise multi-span frames obtained by the stability index (SI) method, and SI is defined by the ratio of PΔ moment to story moment. The SI method calculates the buckling load based on the condition that the story with the maximum stability index is the first to lose its stiffness compared with the other stories at the time of buckling. The analytical parameters used in the present study were the stiffness ratios of beams and columns. The effective length factors obtained by the SI method were compared with the exact effective length factors provided by the buckling slope-deflection method. The story displacement Δ of the PΔ moments was calculated by the application of horizontal forces at the top of the column of each story. This paper outlines a valid process to evaluate the effective length factors using the SI method and demonstrates the impact of the horizontal force distribution and Pδ moments on the accuracy of the SI method in low-rise, multi-span frames.