Tying capacity of web cleat connections in fire, Part 1: Test and finite element simulation

Abstract

The tying capacity of connections between beams and columns is very important in maintaining structural integrity when beam deflections are high due to accidental loads such as fire, but has not so far been thoroughly studied. The project which is the subject of this paper has investigated the robustness of common types of steel connection when subjected to fire. The results reported here concern the performance of web cleat connections in fire, and are drawn largely from experimental investigations. During the testing programme, short cantilever stub beams were subjected to different combinations of shear and tying force. The rotational capacities and resistance to tying forces of their connections at high temperatures were investigated in the presence of other concurrent actions. Test results show that web cleat connections have excellent rotational ductility, and that their resistance reduces rapidly with increase of temperature. Web cleat connections can fail in a number of modes, the selection of which is highly dependent on the connection temperature. Finite element simulations of the test results have been shown to be able to reproduce the behaviour accurately up to the stage at which material failure happens. However, as the ultimate behaviour of connections is often controlled by material fracture, finite element analysis is limited in predicting the ultimate resistance of connections. Investigation of the behaviour of the connection, with some proposed modifications to the general finite element model, showed that finite element analysis can help to interpret the test results and expand the test observations to other similar applications.