Direct strength prediction of web crippling failure of beams under ETF loading

Abstract

This paper proposes a new approach to predict the web crippling failure load of cold-formed steel beams under External Two Flange (ETF) loading using the Direct Strength Method (DSM). After the description of the existing test data, Eurocode 3 [1] and the North-American Specification [2] are used to predict the corresponding web crippling failure loads and the accuracy of such predictions is briefly assessed. In order to obtain additional information on the web crippling behaviour of each test specimen, non-linear numerical simulations are performed. Since the calibration of the DSM-based design expressionsrequires the previous calculation of (i) elastic buckling loads and (ii) plastic strengths/loads, two procedures are presented to achieve these goals. While the buckling loads are determined using the GBTWEB software, specifically developed for this purpose,the plastic loadsare calculated by means of analytical expressions based on yield-line models. By adopting a non-linear regression procedure, the coefficients of a DSM-based formula are determined on the basis of the set of 128 experimental results available and the corresponding buckling and plastic load values. In spite of the different cross-sections, fastening conditions and test setups considered in the calibration procedure, it is possible to establish a clear relationship between the web crippling slenderness and the nominal-to-plastic load ratio. Finally, it is shown that the developed/proposed DSM-basedformula for ETF web crippling design yields reliable predictions, since they are associated with aLRFD (Load and Resistance Factor Design) resistance factor=0.81, which is located within the range of valuescurrently adopted in the 2012 NAS [2].

New developments in the direct strength method (DSM) for the design of cold-formed steel sections under localised loading

“…The DSM design equations have been proposed to predict the capacities of structural members for the EOF load case as given in Eqs. (6) and (7). These equations are the same as the DSM equations for the IOF load case.…”

“…The DSM design equations were proposed for C and Z sections for the IOF and EOF load cases. More recently, Natário, Silvestre and Camotim [7] collected the experimental data from Hetrakul and Yu [8], Young and Hancock [9], Beshara and Schuster [10] and Macdonald et al [11] to investigate the web crippling behaviour of structural members for the ITF and ETF load cases. From the test data, the authors used the yield-line method to calculate the yield load, whereas the buckling load was obtained from GBTWEB software [12] based on a GBT formulation previously developed by the authors.…”

“…slenderness when P n /P y = 1 and k 1 , k 2 , k 3 are coefficients and exponents calibrated through a non-linear regression procedure, fitting the set of P exp /P y ratios to the right-hand side of Eq. (2), which was proposed previously by Natário et al[7]. Different coefficients and exponents are employed for different load cases to build up suitable DSM design equations.For λ ≤ λ o , the nominal inelastic capacity of structural members is based on Eq.…”

07.01: New developments in the Direct Strength Method (DSM) for design of cold‐formed steel sections under localised loading

“…where λ is the sectional slenderness, λ ο is the sectional slenderness when / 1 n y P P = k 1 , k 2 , k 3 are coefficients and exponents calibrated through a non-linear regression procedure, fitting the set of ratios P exp /P y to the right hand side of Eq. (2) which was proposed previously by Natário et al [7]. For different load cases, different coefficients and exponents are employed to build up suitable DSM design equations.…”

“…load cases. More recently, Natário, Silvestre and Camotim [7] collected the experimental data from Hetrakul and Yu [8], Young and Hancock [9], Beshara and Schuster [10] and Macdonald et al [11] to investigate the web crippling behaviour of structural members under the ITF and ETF load cases. From the test data, the authors used the yield-line method to calculate the yield load, while the buckling load was obtained from GBTWEB software [12] which is based on a GBT formulation previously developed by the authors.…”