Modelling concrete slabs subjected to fires using nonlinear layered shell elements and concrete damage-plasticity material

Floor slabs are crucial in the global load bearing mechanism during fire by providing critical alternate load-paths including tensile membrane action. It is desirable, but expensive and difficult, to predict their behaviour accurately with minimal calibration of model parameters. Two new developments are added to OpenSEES for this purpose. First, a thermo-mechanical nonlinear shell element extended for modelling large deflection of slabs in fire along with a multi-layered section to account for temperature-dependent material behaviour including plasticity and thermal expansion. The shell model is ported to include fire induced thermal action definitions induced by real fire exposure, which is critical in accurate simulation of deflections and stress states. Second, a plane-stress formulation of the concrete damage-plasticity material at elevated temperature is introduced to effectively model concrete response and damage in fire. These state-of-the-art developments provide a new, powerful, and open-source tool for researchers and engineers to investigate structural-fire problems at different scales with satisfying accuracy. The code is verified using benchmark solutions and validated by modelling flat reinforced concrete slabs tested at ambient temperature and in fire, followed by simulating the large-scale Cardington Corner fire test. The results of these exercises agree well with analytical and experimental data and show that the new developments are well conceived and implemented.