The development of new Cold-Formed Steel (CFS) channels with staggered slotted perforations has led to advances in improved thermal efficiency of buildings. These new generations of CFS channels reduce the thermal bridging effect interrupting the direct heat transfer across the web. However, the integration of these staggered perforations creates challenges in terms of reduced structural capacity. It is therefore vital to study the structural behaviour under various loading scenarios. Therefore, the web crippling performance of staggered slotted perforated channels under End-One-Flange (EOF) loading condition and flanges unfastened to bearing plate was investigated in the present paper. Finite Element (FE) models were developed to capture the web crippling strength and failure mechanism of these staggered slotted perforated channels. The validity of the FE modelling techniques was ensured by comparing the web crippling experimental results of CFS channels with solid and perforated webs under the EOF loading. Upon validation, an extensive parametric study comprising 360 FE models was then performed with the aim of (i) examining the effect of staggered slotted configurations and (ii) the corresponding degree of web crippling strength reduction. The results provided a direct mean of notable web crippling strength reduction up to 74%. The numerically derived data points were used to develop a reduction factor based new design equation, which can directly be applied to predictive equations of web crippling. The proposed approach yields more accurate and consistent strength predictions and improves the understanding of CFS channels with staggered slotted perforations.
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The authors would like to acknowledge the financial support and research facilities provided by Northumbria University .
As specified in CFS design codes, the design provisions to estimate the web crippling failure loads under the EOF loading are presented herein. The European standard, EN1993-1-3 , employs different equations to estimate the bearing (crippling or buckling) failure strength for sections subject to support reaction or local transverse force applied through the flange. The North American (AISI S100 ) and Australian/New Zealand (AS/NZS 4600 ) standards provide a unified design equation for the web crippling strength estimation, and the coefficients are selected according to the loading type and flange restrained conditions. The AS/NZS 4600  and AISI S100  design approaches were also modified by Sundararajah et al.  based on experimental and numerical results to enhance their accuracy. The design equation to estimate the web crippling strength of CFS channels without web holes under EOF loading and flanges unfastened to support conditions are summarised in Table 10. The specific limitations to use these design equations are also given in Table 10, and detailed limits can be found elsewhere [5,6,8].The comparison of reduction factors obtained from parametric FE analysis with the proposed reduction factor is depicted in Fig. 18 for different web slenderness values. The comparison demonstrates good agreement. The developed reduction factor formula Eq. (6) can be directly used in Eq. (1) for qs. Therefore, the equation to estimate the web crippling strength of staggered slotted CFS channels under EOF loading and flange unfastened to support condition is presented in Eq. (7).The increased use of a new generation of staggered slotted perforated channels has motivated researchers to conduct several studies for providing structural design guidance to practising engineers. As a part of that, the web crippling performance of CFS channels with staggered slotted perforations under EOF loading and flanges unfastened to the support condition has been investigated in this paper. FE models of CFS channels with and without web holes were created and validated with web crippling test results of CFS channels under EOF loading. The validated FE models were extended for parametric FE analysis of CFS channels with staggered slotted perforations. The parametric study included 288 FE models of staggered slotted perforated channels and 72 FE models of corresponding solid web channels (without web perforations). The results show that staggered slotted perforations led to considerable web crippling strength reduction, and the maximum strength reduction obtained was 74% (qs = 0.26). Moreover, the failure modes indicated a formation of local yielding zones around the corners of staggered slotted perforations. The existing design codes EN1993-1-3 , AS/NZS 4600  and AISI S100  do not include design provisions for these new generations of CFS channels under web crippling actions. Instead, these design codes employ design provisions for discrete web holes. Having analysed the obtained results throughout the parametric study, a new design equation was developed (Eq. (7)) to estimate the web crippling strength of staggered slotted perforated channels under EOF loading. This newly developed equation provides more suitable results and is useful for the practicing engineers.The authors would like to acknowledge the financial support and research facilities provided by Northumbria University.
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