Membrane-Flexural Failure Modes of Restrained Slabs

The investigation of compression-membrane action in restrained slabs involves elasto-plastic analysis, including the effect of change in geometry during the deformation, followed by rigid-plastic solutions. This procedure leads to the predictions of the loading capacity, magnitude of the restraining forces, and the effects of the boundary conditions, the span to depth and reinforcement ratio. Underreinforced thin slabs are associated with geometrical instability, thick underreinforced slabs with plastic instability, and thick overreinforced slabs with compression failure. In thick slabs, the confined compressive stress leads to an improved loading capacity and modification of the definition of balanced reinforcement. In modified underreinforced slabs, low reinforcement ratios lead to tensile failure, while high ratios lead to initial compression failure followed by tensile failure. The restraint depth of an internal panel in multipanel slabs can be controlled by proper reinforcement design. This panel loses its restraint if surrounded by a slab strip width less than half the panel span, and is fully restrained if this width is more than twice the span.