Design and Optimization of Cold-Formed Steel Sections in Bolted Moment Connections Considering Bimoment

Abstract

The load transfer mechanism in cold-formed steel (CFS) bolted moment connections is mainly through the bolt-group in the web of beam elements, which may lead to relatively large bimoment and warping deformation. While the bimoment effects can be considered in the Direct Strength Method (DSM), ignoring the bolt-group length in the conventional design process can lead to non-conservative solutions. This paper presents an alternative analytical design approach using Eurocode 3 (EC3) effective width method to determine the ultimate flexural strength of CFS bolted moment connections by considering bimoment effects. The results compare very well with previously published experimental test data as well as detailed finite element models developed in this study. It is shown that a short boltgroup length may lead to up to 25% reduction in the flexural strength of the CFS bolted connections.However, a longer bolt-group length generally results in a moment capacity almost equal to the flexural strength of the CFS channel section. Shape optimisation is then conducted using a Genetic Algorithm (GA) to improve the flexural capacity of the connections by taking into account the bimoment effects.The main design variables are considered to be the relative CFS beam cross-sectional dimensions, while the plate slenderness and dimension limits suggested by EC3 as well as a number of manufacturing and practical end-use constraints are incorporated as design constraints. It is found that, compared with standard cross-sectional dimensions, the optimised sections can improve the flexural strength by as much as 36% for the bolt-group length equal to the depth of beam element.

Constrained optimization of anti-symmetric cold-formed steel beam-column sections

“…More recently, a coupled optimization framework at the element and structural levels was developed by Phan et al [36] to find the optimum solutions for the CFS portal frames. They also conducted shape optimization to improve the flexural capacity of the CFS beam members used in bolted moment connections by taking into account the bimoment effects [37].…”

Numerical Evaluation of the Upright Columns with Partial Reinforcement along with the Utilisation of Neural Networks with Combining Feature-Selection Method to Predict the Load and Displacement

“…Numerical evaluation of racking systems currently is a typical approach to derive the optimum values of CFS sections and upright characteristics. Two famous numerical approaches including finite strip method and direct strength method were conducted along the genetic algorithm (GA) [25,26] to obtain the best possible upright columns [27][28][29][30]. In this study, various lengths and thicknesses of cold-formed uprights were modelled by ABAQUS with different reinforcement distances.…”

Optimisation of cold-formed steel beams for best seismic performance in bolted moment connections

“…Several studies have experimentally and analytically investigated the structural performance of apex and eaves CFS connections under monotonic loads (e.g. [11][12][13][14][15][16][17][18][19][20][21]). It was concluded that the local buckling of CFS beam close to connection zone was normally identified as a dominant failure mode, while it was shown that bolt-group size can have a significant effect on the flexural strength of the connections.…”

“…Bučmys et al [24] presented an analytical approach to determine the rotational stiffness of CFS bolted moment connections based on the component method stipulated in Eurocode 3 [25]. In other relevant studies, Rinchen and Rasmussen [16] and Phan et al [19] developed design approaches for the flexural strength of bolted connections by considering the effects of bimoment. The design aspects of the CFS bolted moment connections were further explored by Mojtabaei et al [20], who attributed premature failure in the web of the cross-section to the shear lag effect.…”