Optimization of failure modes of a ductile connection under fire conditions

Connections are the most vulnerable parts of a structure under fire conditions. A novel steel connection with high axial and rotational ductility has been proposed with the objective to improve the performance of steel-framed buildings in fire. Analytical model has been developed to determine the axial displacement of the top and bottom flanges of the beam end at high temperatures. A series of sub-frame models with this ductile connection have been built using Abaqus to study the influence of the characteristics of the connection part between the fin-plate part and face-plate part on the overall connection behaviour. The current critical failure mode of the ductile connection is bolt pull-out from the face-plate zone, and the tensile deformation capacity of the connection is not fully utilized. Therefore, measures to improve the bolt pull-out failure mode of the connection have been tested using the Abaqus sub-frame models, including adding a strengthening plate to the face-plate part of the connection and increasing the connection plate thickness. The simulation results show that the bearing failure of the beam web will become another critical failure mode of the connection, once the bolt pull-out failure is eliminated. To further optimize the high-temperature performance of the connection, the Abaqus steel frame models have also been used to test some measures to delay the occurrence of the beam web bearing failure, including adding strengthening plates to the part of the beam web in contact with the connection, and improving the material properties of the part of the beam web around the bolt holes at high temperatures.