Abstract
The objective of this paper is to investigate the buckling behavior and design method of the ultimate strength for the cold-formed steel (CFS) built-up I-sectional columns under axial compression which failed in distortional buckling and interactive buckling. A total of 56 CFS built-up I-sectional columns subjected to axial compression were tested, and the different buckling modes and ultimate strengths were analyzed in detail by varying the thickness, the length, the spacing of screws, the end fastener group, and the cross-sectional dimensions of CFS built-up I-sectional columns. It was shown in the test that noticeable interaction of local and distortional buckling or interaction of local, distortional, and global buckling was observed for the built-up I-sectional columns with different lengths and cross-sectional dimensions. A finite element model (FEM) was developed and validated with experimental results. A further parametric study has been conducted including different cross sections and slenderness ratios for the built-up I-sectional columns. The load-carrying capacities obtained from the experimental and numerical study were used to investigate the feasibility of the current direct strength method (DSM) when DSM was applied to CFS built-up I-sectional columns. The comparison results showed that the current DSM is not safe for CFS built-up columns failed in distortional buckling and interactive buckling. Therefore, the improved design formulas were proposed, and their accuracy was verified by using finite element analysis (FEA) and experimental results of CFS built-up I-sectional columns subjected to axial compression.
Highlights
Introduction e use ofcoldformed steel (CFS) members has become increasingly popular during the past few decades because CFS has high strength and stiffness, convenient manufacturing and transportation, and a high construction speed
“Technical Specification for Low-Rise Cold-Formed in-Walled Steel Buildings” (JGJ227-2011) [1] specifies that the ultimate strength is the summation of the ultimate strength of both individual member for the built-up I-section column. e 2016 AISI Specification [2] specifies that the ultimate strength of built-up I-sectional columns should be predicted with a modified slenderness ratio (KL/r)m by considering the effect of shear force between individual sections; the modified slenderness ratio can be predicted by using the following formula:
Design Method e effective width method (EWM) and direct strength method (DSM) are two basic design methods for CFS members in the worldwide design specifications. e DSM is only selected to determine the ultimate strength of the CFS built-up I-sectional columns in this paper
Summary
Experimental Study and Direct Strength Method for Cold-Formed Steel Built-Up I-Sectional Columns under Axial Compression. E objective of this paper is to investigate the buckling behavior and design method of the ultimate strength for the coldformed steel (CFS) built-up I-sectional columns under axial compression which failed in distortional buckling and interactive buckling. E effects of cross section and length of the member on the buckling behavior of the built-up columns connected with four U-sections were tested by Anbarasu et al [10], which showed that DSM cannot predict the ultimate strength of this kind of section. Li et al [13, 14] investigated the ultimate strength of CFS box columns by test and numerical analysis and proposed the design method to predict the load capacities of the built-up box members.
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