Strut-and-tie model for punching shear of concrete slabs

Tiller, Richard W. (1995) Strut-and-tie model for punching shear of concrete slabs. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (10MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

The reinforced concrete slab system is an economical and popular structural slab system in building and offshore construction. A major concern of this system is localized punching shear failure at the slab-column interface. Punching shear failure occurs when the column "punches" through the slab. This type of failure is unpredictable and often sudden resulting in cathastrophic failure of the slab system. -- Current North American design codes deal with punching shear in an empirical equation based mainly on test results. This approach is limited to concrete with a compressive strength generally less than 40 MPa. The strut-and-tie method considers the flow of forces in a reinforced concrete element to consist of a series of compressive struts and tension ties joined at nodes. The strut-and-tie method is a rational approach to structural concrete design which results in a uniform and consistent design philosophy. -- A strut-and-tie model has been developed to model the punching shear behaviour of a concrete slab. This model provides a quick and simple approach to punching shear behaviour. It is applicable for both normal and high strength concrete under symmetric and nonsymmetric loading with and without shear reinforcement. -- The strut-and-tie model for symmetric punching consists of a "bottle shaped" compressive zone in the upper section of the slab depth leading to a "parallel stress" compressive zone in the lower section depth. Inclined shear cracking develops in the bottle shaped zone prior to failure in the lower zone. Cracking in the bottle shaped zone is related to the diagonal tensile strength of the concrete. Ultimate punching failure occurs in the parallel stress zone by a high radial compressive stress failure. An equation based failure criteria for the strut-and-tie method is used to model the behaviour in the lower compressive stress zone. The results of the strut-and-tie model for symmetric punching shear behaviour were compared to experimental test results performed and published by others. The results of the strut-and-tie model showed excellent agreement with these test results. -- A strut-and-tie model was also developed to rationally model nonsymmetric punching shear behaviour due to unbalanced moment transfer and symmetric punching behaviour of concrete slabs with shear reinforcement. These models showed excellent agreement with test results performed and published by others. -- The strut-and-tie method presents a unified, consistent, rational behaviour model for structural concrete elements including the punching shear phenomena of concrete slabs.

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