Surround stiffness to membrane action in concrete slabs

Abstract

Previous attempts to provide a convenient analysis enabling realisation of the very significant benefits of membrane action in concrete slab design have made use of rigid–plastic analysis modified by assuming a linear elastic in-plane perimeter at the mechanism boundary. There are compelling reasons why these methods or any consideration of membrane action in slab design are still not routinely employed in design. There is a lack of information on the value of the appropriate boundary stiffness that may arise from the various slab surroundings in construction. Furthermore, previous tests have generally not confirmed predictions from theories based upon a straightforward in-plane boundary stiffness. The present paper suggests that, where a failure mechanism occurs entirely within the overall slab area, the surrounding slab alone may be considered to provide the membrane boundary restraint. This conveniently requires only the properties of the slab itself and may be regarded as providing a lower bound to membrane enhancement. The paper then shows that an improved representation of edge restraint, which considers the interaction between in-plane and rotational stiffness of the slab, provides much more promising agreement with load–deflection behaviour found in previous tests. Until more information becomes available on the additional influences of various support systems, the new model could form the basis for future design taking advantage of the considerable benefits of membrane action.