Novel structural details to mitigate progressive collapse in steel nominally-pinned joints

Abstract

Steel structures are frequently used worldwide. The beam-column connections play a vital role in those structures. In a case of column removal due to blast, fire or vehicle impact, the disproportionate collapse can occur if the robustness of the joint is not enough and the failure propagates to other members. Current design practices require that the beam-column joints shall withstand a minimum tie force to prevent progressive collapse. However, several pieces of research have shown that nominally pinned joints which are commonly used in steel frames cannot provide the required tie force while undergoing significant rotations imposed by a column removal event. The present thesis proposes a set of novel structural detail to be added to the steel nominally pinned joints to arrest progressive collapse by enhancing both their tensile resistance and rotation capacity. The proposed structural details exploit the exceptional strength and ductility of Duplex stainless steel pins (SSPs) under bending which allows them to withstand excessive deformation prior to their fracture. First, the monotonic fracture capacity of SSPs was experimentally evaluated followed by the calibration of numerical models with the capability of predicting fracture of SSPs. Employing the calibrated numerical models, a set of parametric study was carried out on various geometry properties of SSPs to develop a design procedure to reliably achieve the required levels of tie force and rotation in a joint. An experimental programme including static and dynamic tests on the proposed joint was presented, discussed, and simulated in Abaqus. In addition, more analyses were conducted to determine the Dynamic Increase Factor (DIF). Finally, the proposed joint was modelled as a 3D connection including the primary and secondary directions. It was observed that the proposed joint significantly increases the joint rotation while providing appreciable tie force compared to standard fin plate connection.