Shear bolted connections: numerical model for a ductile component, the plate in bearing

Abstract

In order to achieve a full plastic distribution of forces in a shear bolted connection, ductility is required to the steel plate and to the plate-bolt contact zone in the firstly loaded bolt rows. Knowing that bolts present a brittle behavior, deformation capacity has to be obtained from ductile components as the plate-bolt in bearing. In the present paper a numerical model is proposed to evaluate the plate-bolt in bearing component. The main objective is not only to achieve it elastically but to obtain a good approximation of the post-elastic response. The proposed model has been successfully validated by experimental tests on shear bolted connections performed at the Delft University of Technology and at the University of Ljubljana. The EC3 Part 1.8 [1] approach, to evaluate resistance and initial stiffness of the plate-bolt in bearing component, is included in the comparison and discussion of results. 1 ITRODUCTIO In shear bolted connections forces are transferred from one plate to another (others) by plate-to-bolt contact. Neglecting the small friction developed between plates and the negligible bending of the bolt, four sources of resistance and deformation modes should be considered: bearing of the plate and/or bolt; shear in the plates; tension in the plates; shear in the bolt shanks. In these types of connections, the load to be transferred between the plates is distributed non-uniformly amongst the bolt-rows (Figure 1). In [2], Ju et al showed that in the nonlinear range the maximum load achieved by the connection is almost linearly proportional to the number of bolts in the connection. According to [1], a full plastic distribution of forces can be assumed as long as the connection length is limited. Pietrapetrosa el al [3] studied fitted bolted connections and showed that, inside the limits given by the code and by practical guidance, sufficient ductility to achieve a full plastic distribution of internal forces is available. On the other hand, Wald et al [4] verified that if imperfections (misalignment of bolts) are considered, failure could be first attained in the extreme bolts and therefore a full plastic resistance was not reached. The presence of imperfections requires therefore higher deformation capacity from the connection components. Knowing that the bolt has a brittle behavior, ductility has to be obtained from the plate-bolt in bearing component in order to achieve a full plastic resistance, as observed in [5] In EC3 Part 1.8 [1] the bearing resistance and the bearing stiffness may be determined using the proposed design functions. However, these functions are mainly directed to mild steel and to connections with normal round holes. So, in this paper, the calibration of a numerical model to study the plate-bolt in bearing component, which can be later used to extend the actual knowledge to new common practices (connections with High Strength Steel, oversized or slotted holes, etc), is presented. Tests made on shear bolted connections at the University of Ljubljana and at the Delft University of Technology are used to