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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 59
Edited by: B.H.V. Topping and B. Kumar
Paper VI.2

Punching Shear Capacity of Internal Column-Flat Slab Junctions with Inplane Restraint: A Comparison Between Finite Element Predictions and Experiments

P. Bhatt and B.T. Lim

Department of Civil Engineering, University of Glasgow, Scotland

Full Bibliographic Reference for this paper
P. Bhatt, B.T. Lim, "Punching Shear Capacity of Internal Column-Flat Slab Junctions with Inplane Restraint: A Comparison Between Finite Element Predictions and Experiments", in B.H.V. Topping, B. Kumar, (Editors), "Developments in Analysis and Design using Finite Element Methods", Civil-Comp Press, Edinburgh, UK, pp 141-147, 1999. doi:10.4203/ccp.59.6.2
The problem of punching shear strength of flat slabs with or without moment transfer but with no in-plane restraint has been the subject of extensive experimental study. Much of this data has been used to develop empirical design equations given in codes of practice. However it is well known that in-plane restraint is always present either due to actual in-plane restraint provided in the form of edge beams but more commonly provided by the rest of the slab away from the zone of punching. Experimental work shows that this in-plane restraint significantly increases the punching shear capacity of the slab. However codes of practice in general do not consciously allow for the enhancement mainly due to the difficulties encountered in including it in a rational way In previous works, the authors successfully used 3-D non-linear finite element analysis based on a 20 node isoparametric element for predicting punching shear strength of interior flat slab column junction without moment transfer or for interior, edge and corner slab - column junctions with moment transfer but ignoring the in-plane restraint. The program used the non-linear elastic isotropic model, proposed by Kotsovos, to model concrete behaviour, while steel was modelled as an embedded clement exhibiting elastic-perfectly plastic response Allowance was made for shear retention in concrete after cracking and also for tension stiffening. Only fixed direction, smeared cracking modelling was adopted. Particular attention was paid to judge using several criteria based on predicted behaviour, the likely mode of failure and that it matched well the observed mode of failure. The object of the present investigation is to see how far the same non-linear program can be used to predict the shear failure of slabs with in-plane restraint. It has to be emphasised that the analysis is based considering small deformation only and no attempt was made to include enhancement in strength due to large geometric changes. 44 slabs covering a very wide range of in-plane restraint and including variables such as percentage of flexural steel, effective depth to span ratio and tested by three different investigators were analysed. Good agreement was observed between predicted ultimate load and the experimentally measured load. It is concluded that the present program can confidently be used to predict the ultimate failure load in practice.

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