Nonlinear analysis of moderately thick reinforced concrete slabs at elevated temperatures using a rectangular layered plate element with Timoshenko beam functions

A simple displacement-based 4-node, 24-DOF rectangular layered plate element for nonlinear finite element analysis of thin-to-moderately-thick reinforced concrete slabs subjected to combined external and thermal loading is developed in this paper. Timoshenko's composite beam functions are extended to form the basis of the bending strain of the layered plate element developed herein, so that the proposed model and approach not only provide a unified formulation for thin and moderately thick plates, but also avoid shear locking naturally. In addition to temperature-dependent material nonlinearity, geometric nonlinearity is accounted for to include the tension membrane effect, which has been identified as the major contributor to the load carrying capacity of RC slabs at elevated temperatures. Based on the proposed element model, the updated Lagrangian approach is employed to formulate the nonlinear finite element analysis and solution procedures for the nonlinear analysis of reinforced concrete slabs under constant external loading and thermal loading which are proposed in this paper. Comparison of the results from the proposed model and previous literatures for the numerical analysis of reinforced concrete slabs at ambient and elevated temperatures have demonstrated the effectiveness of the proposed model and solution procedures.