Reinforced concrete slabs with partial lateral edge restraint

 A A Olonisakan

It is well-known that compressive membrane (arch or dome) action in reinforced concrete slab systems, arising from total or partial restraint of lateral expansion at the edges of the slab, can increase the peak-load capacity of the slab to several times the value predicted by the conventional yield-line theory or any simple bending theory for the same slab unrestrained. While this phenomenon is widely being relied upon as an added safety factor in the design of slab structures, no well-defined and generally agreed procedure has yet been developed to assess its effects in the design of laterally restrained slabs.

In this dissertation, numerical models for tackling the problem of compressive membrane action in uniformly-loaded one-way slabs and two-way square slabs, with partial lateral edge restraints, are proposed. Much emphasis is placed on speed and simplicity, and the ability of the proposed method to reproduce the short-term load-deflection response of the slabs, in full detail, throughout the entire load range. The calculation procedure, based on the Galerkin method, incorporates a modified constant arc-length method for getting over difficulties in convergence to a solution at or beyond peaks on the non-linear load-deflection curve. The theoretical predictions are validated against the results of laboratory tests on reinforced concrete slab models, with limited lateral restraint stiffnesses, subjected to uniform or simulated uniform transverse loading. The proposed numerical models are shown to give rapid and realistic solutions, with complete load-deflection curves, and reasonably good correlation with experimental results.

Computer programs for the thorough analysis of partially restrained one-way slabs and two-way square slabs under uniform load are developed. It is thought that these computer programs, probably more convenient than ordinary non-linear finite element solutions, could be valuable to design engineers, in allowing rapid predictions of the salient features of slab behaviour.

Keywords: Compressive membrane action, partial lateral edge restraint, reinforced concrete slab, in-plane slab stiffness, load-deflection curve, Galerkin method.