Structural assessment on beam-slab reinforced concrete sub-structures under column loss scenario

Abstract

Mobilisation of alternate load path (ALP) mechanisms in 3D beam-slab systems is a key factor in designing structures against progressive collapse. Existing analytical methods on 3D beam-slab systems focusing on limited load-resisting mechanisms often lead to uneconomical and unrealistic design, while finite element models with 3D solid elements are too complicated and time consuming for 3D beam-slab systems. To address these shortcomings, this paper aims to provide structural engineers two simple but effective and reliable approaches to predict structural behaviour of 3D beam-slab systems. They include (i) an analytical method and (ii) a simplified finite element model based on strip method and grillage analysis. Both approaches are validated against published test results for 3D beam-slab systems. Compared to existing approaches on 3D beam-slab systems, these two proposed methods incorporate all the load resisting mechanisms in both the beams and slabs, giving more accurate and realistic predictions of load-displacement curves for the sub-structures considered. In addition, parametric studies on the analytical approach are presented to shed light on the role of boundary conditions and the contribution of slabs to load resistance capacity of 3D beam-slab structures against progressive collapse.