Membrane Action, and Design Against Punching Shear

This paper is concerned with the design method for providing resistance against punching shear for flat slabs where the slab extends substantially up to the surrounding supports - e.g. an internal panel of a multibay flat slab. A signifcant aspect generally ignored in the design of flat slab structures is the development of what is commonly referred to as membrane action. When a load is applied to the slab, the deflection of the slab is accompanied by an outward expansion of the slab boundaries. This tendency to expand laterally is restrained by the supporting columns, beams or walls. The adjacent area of the slab also acts as a stiff restraining diaphragm. This membrane action induces internal axial compressive stresses that significantly influence and enhance the punching shear resistance of the slab. The design method is developed on the basis of a test programme jointly funded by the Department of the Environment and the British Cement Association. The specimens were 9m x 9m in plan and 250mm thick and represented an area of slab surrounding an internal column of a continuous flat slab. It is shown that there is a significant increase in punching shear resistance compared with the smaller conventional specimens. A design method taking membrane action into account is proposed.

P.S. Chana and S.B. Desai