Seismic Moment End Plate Joint Performance Under Fire Conditions

Large fires in buildings cause structural member strength and stiffness losses, and detrimentally affect the behaviour of structural systems. Restrained thermal expansion induces compressive forces into beams during the early stages of heating together with large deflections. At high temperatures, large deflections and catenary tension forces develop. During cooling, tensile forces increase. The resulting beam actions due to the heating and cooling lead to large rotational and moment demands at beam connections. Moment-resisting joints in earthquake-prone regions have specific detailing to ensure good seismic performance. They must resist reversing overstrength moment demands while preventing the development of inelastic demands in non-ductile components. This paper seeks to evaluate if seismic-purpose moment end plate joints perform better than non-seismic connections under fire conditions. An extended endplate designed following the British SCI P398 guidelines, representing the non-seismic-purpose detail is considered. Also, a New Zealand seismically-designed moment endplate, which uses a thicker end plate and larger bolts symmetrically placed to provide equal hogging and sagging capacity is used for comparison. A finite element analysis is conducted using ABAQUS to compare the performance of these joints subjected to the ISO834 fire with and without cooling. The analysis shows that the New Zealand details result in a failure time approximately the same as the British detail for the cases considered. Failure is governed by plastic hinge formation beside the joint. The British end plate and bolts exhibit significantly more inelastic deformation. When a cooling phase is considered, both joints showed increased inelastic deformations.