Title: Combined Beam-Slab Collapse Mechanism in Isolated Reinforced Concrete Beam-Slabs—Strength Design and Load Testing

Author(s): Anurag Singh, Bijily Balakrishnan, and Devdas Menon

Publication: Structural Journal

Volume: 118

Issue: 3

Appears on pages(s): 223-240

Keywords: beam-slab system; combined beam-slab failure; rational design methodology; slab alone failure; yield line analysis

DOI: 10.14359/51730527

Date: 5/1/2021

Abstract:
In the conventional method of strength design of reinforced concrete (RC) beam-slab systems, it is assumed that if the beams are adequately stiff, the slab and beams can be analyzed and designed separately under factored gravity loads. This paper demonstrates, through yield line analysis and load testing of isolated beam-slab systems, that such a design, which tacitly assumes a ‘slab alone failure’ mechanism, is irrational and overconservative (failing at a load level much higher than expected). The actual collapse of the conventionally designed beam-slab system invariably involves a combined beam-slab failure mechanism. It is therefore more rational and economical to design explicitly for such a collapse mechanism, accounting for plastic hinge formation in the beams along with yield lines in the slab. The proposed method suggests provision of minimum slab steel (as prescribed by the design code), and then designing the beams aiming for a combined two-way beam-slab failure. Experimental load testing establishes that the collapse occurs as planned and that the proposed economical design has the desired code-specified safety margins.