DSM for Web Crippling under Two-Flange Conditions

This paper summarizes recent investigations on the development of Direct Strength Method (DSM) for the design of cold-formed steel beams under two-flange (TF) loading against web crippling failure. Recently, the authors proposed a new approach to predict the web crippling failure load of cold-formed steel beams under External Two Flange (ETF) and Internal Two Flange (ITF) loadings using DSM. Firstly, existing experimental test data are summarized and then the accuracy of North-American Specification (AISI 2012) and Eurocode 3 (CEN 2006) provisions is briefly assessed. In order to obtain additional information on the web crippling behavior of each test specimen, non-linear numerical results are obtained. Since the calibration of the DSM-based formula involves the previous calculation of (i) elastic buckling load and (ii) plastic load, two procedures are presented. Buckling loads are determined using the GBTWEB software, intentionally developed for this purpose, while plastic loads are calculated using analytical expressions based on yield-line models. By adopting a non-linear regression, the coefficients of DSM-based formulae are determined using a set of 128 (ETF) and 130 (ITF) test results and the corresponding estimates of buckling and plastic loads. The DSM-based formulas for ETF and ITF web crippling design are successfully proposed and the resistance factors (LRFD) obtained are φ=0.81 (ETF) and φ=0.75 (ITF)