Lim, Boon Tiong
Punching shear capacity of flat slab-column junctions (a study by 3-D non-linear finite element analysis).
PhD thesis, University of Glasgow.
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This thesis presents a study of punching shear capacity of flat slab-column junctions. A three dimensional non-linear finite element program based on 20 node isoparametric solid element was used for the investigation. The non-linear 3-D elastic isotropic model proposed by Motsovos was used to describe the behaviour of concrete before cracking or crushing. After cracking, a yield criteria for 2-D model similar to Kupfer-Hilsdorf was used and concrete was assumed to be anisotropic. No softening in compression is assumed. Smeared crack approach with simple tension stiffening and shear retention equations were employed to mimic the post-cracking behaviour of concrete. Reinforcing bars were represented by one dimensional element embedded in the solid elements and for both tension and compression, linear elastic-plastic behaviour is assumed.
A comparison was first made between the predictions of slab behaviour using Kotsovos' model (In-house program) and plasticity based model used in the commercial package ABAQUS. From this it was concluded that Kotsovos' concrete model is a good model for the three dimensional analysis of the punching shear problem but the ABAQUS model was unsuitable.
In order to achieve an accurate and economical solution for the non-linear analysis, a parametric study was carried out to choose a suitable analytical model. After having chosen the "best" concrete model, over 175 slabs from different sources were analysed using a constant set parameters. The analysis includes various types connections (interior, edge and corner) with and without shear reinforcement, subjected to shear force alone or to a combination of shear force and unbalanced moment. These slabs cover most of the factors affecting punching shear strength, such as slab thickness, flexural reinforcement ratios, concrete strength, and column size. This study also includes the effect of in-plane restraint on punching shear strength of slabs.
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