07.04: Web crippling design of hollow flange channel beams under one flange load cases

Abstract

The advantage of having no unstiffened elements coupled with material located away from the neutral axis makes hollow flange channel (HFC) beam sections structurally efficient in bending when compared with other commonly used open cold-formed steel sections. This concept is similar to hot-rolled steel sections such as the universal beam and channel beam sections, which are very efficient in bending. However, the hot-rolled sections are heavier, torsionally weak, and have low resistance to flexural-torsional buckling. The two hollow flanges in HFC beams make them torsionally strong and also eliminate the occurrence of distortional and local flange buckling modes in most cases. However, HFC beams have slender webs, making them vulnerable to web crippling failure modes. To understand the web crippling behaviour of HFC beams and develop accurate design rules, finite element models of HFC beams were developed and validated using available experimental results under End One Flange (EOF) and Interior One Flange (IOF) load cases. Using the validated finite element models, a detailed parametric study was conducted for many HFC sections. Finite element analyses provided the required elastic buckling and ultimate loads of HFC beams in web crippling (EOF and IOF load cases). New predictive equations were proposed to determine the elastic buckling coefficients of HFC beams, followed by Direct Strength Method (DSM) based design rules using the test, elastic buckling and nonlinear analysis results from finite element analyses. This paper presents the details of the web crippling design rules developed based on the detailed numerical study on the web crippling behaviour of hollow flange channel beams under one flange load cases.