SOFTENING AND SNAP-THROUGH BEHAVIOR OF REINFORCED ELEMENTS

The writers present a fracture mechanics model for reinforced concrete collapse, which is a refinement of that proposed previously, based on compliance and stress-intensification concepts. In this case, a crack-opening displacement congruence condition replaces the rotational congruence condition, while the reinforcement reactions are applied directly to the crack surfaces and not as closing forces at infinity. The theoretical results confirm a transition from ductile to brittle collapse by varying a nondimensional brittleness number defined in previous contributions. In addition, with the present model, yielding or slippage of reinforcement can precede or follow crack propagation in concrete. The moment-versus-rotation response presents softening and snap-through behaviors and is substantially in agreement with the experimental results. Such a theoretical approach appears to be very useful in estimating the minimum reinforcement for members in flexure.