Finite element investigation on the structural behaviour of cold-formed bolted connections

A finite element model with three-dimensional solid elements was established to investigate the bearing failure of cold-formed steel bolted connections under shear. It was demonstrated (Chung and Ip. Engineering Structures 2000;22:1271-1284) that the predicted load-extension curves of bolted connections in lap shear tests followed closely to the measured load-extension curves provided that measured steel strengths and geometerical dimensions were used in the analysis. Furthermore, it was shown (Chung and Ip. Proceedings of the Second European Conference on Steel Structures, Praha, May 1999, p. 503-506) that stress-strain curves, contact stiffnesses and frictional coefficients between element interfaces, and clamping forces developed in bolt shanks were important parameters for accurate prediction of the deformation characteristics of bolted connections. This paper presents an extension of the finite element investigation onto the structural behaviour of cold-formed steel bolted connections, and three distinctive failure modes (Ip and Chung. Proceeding of the Second International Conference on Advances in Steel Structures, Hong Kong, December 1999) as observed in lap shear tests are successfully modelled: bearing failure; shear-out failure; and net-section failure. Furthermore, a parametric study on bolted connections with different configurations is performed to provide bearing resistances for practical design, and the results of the finite element modelling are also compared with four codified design rules. It is found that the design rules are not applicable for bolted connections with high strength steels due to reduced ductility. Consequently, a semiempirical design formula for bearing resistance of bolted connections is proposed after calibrating against finite element results. The proposed design rule relates the bearing resistances with the design yield and tensile strengths of steel strips through a strength coefficient. It is demonstrated that the design rule is applicable for bolted connections of both low strength and high strength steels with different ductility limits.