Unified analytical and design-oriented models for compressive and tensile membrane actions in RC beam-slab structures under internal column loss

Abstract

Resisting mechanisms including compressive membrane action (CMA) and tensile membrane action (TMA) are critical for RC beam-slab structures against progressive collapse. However, due to the difficulties in considering the nonlinear behaviors and beam-slab interactions, limited analytical studies are currently available to accurately determine the whole resistance evolution path, let alone a simplified design model. This study presents a unified analytical model and a design-oriented simplified model to predict the whole resistance displacement of RC beam-slab substructures under internal column loss. Both equivalent uniformly distributed load (EUDL) and concentrate load (CL) conditions have been considered. In the analytical model, the beam-slab system is discretized into interior beams and multiple slab strips with consideration of their interaction. The compatibility and equilibrium conditions, curvature equations, and constitutive laws of concrete and reinforcement are incorporated to analyze each beam and slab strip. In the design model, a new strategy is proposed to decompose the structural resistance of membrane effect into summation of two components, CMA and TMA resistances, with explicit expressions. Both developed models are validated through experimental and numerical results and good agreements are achieved. Results of the analytical model show that ignoring the beam-slab interactions can lead to underestimation of structural resistance, especially during the transition from the CMA to TMA. The locations of loading points should be carefully selected to make sure 12-point loading system effective. A rule is also suggested to determine proper locations. The simplified design method gives slightly conservative predictions of structural resistance, and its calculation is easy for engineers to use.