The effect of load-induced thermal strain on flat slab behaviour at elevated temperatures

Several recent sets of experimental results on the punching shear behaviour of flat slabs in fire have produced apparently anomalous deflections results, where the slab deflections on heating are in the opposite direction to that expected if arising from free thermal expansion. Using numerical analysis, this paper shows that the results are explained by load-induced thermal strains (LITS). Using two independent modelling approaches, the profound effect of LITS on deflection behaviour is demonstrated. The findings have implications for the design of flat-slab structures to resist fire because ignoring LITS may result in non-conservative design predictions.