Nonlinear analysis of reinforced concrete structural slabs
Nonlinear response of a structure to progressive loading may originate from two different sources viz, geometric nonlinearity and material nonlinear behaviour. For a rationally proportioned concrete structure, the material nonlinear responses are believed to contribute the major part of its total nonlinear behaviour. Geometric nonlinearities, become significant only when the structure is relatively slender. It is the material nonlinearities of reinforced concrete structures that are of interest in this investigation. Two plate bending finite elements have been generalised to include coupling of inplane actions with the bending effects. This was achieved through layering concept. One of these elements had been employed by some previous researchers. But the present formulation is different from theirs in that a numerical integration scheme is introduced to evaluate the stiffnesses and internal equivalent forces. A number of schemes for solving the nonlinear equations have been included in the present formulation. Suitability and effectiveness of these schemes in tracing the material nonlinear responses of concrete slabs have been examined. The numerical material model behaviour is based on the experimental observation reported by various authors. Readily available material characteristic properties are used in the description of the model. The overall response of reinforced concrete slabs is found to be significantly influenced by the cracking and post cracking treatment of concrete. Some form of tension stiffening scheme seems necessary to represent the structural response realistically. A number of conventional tension stiffening schemes have been incorporated, including a simple alternative formulation. The effect of different tension stiffening schemes and some other numerical parameters on the numerical solution of concrete structures have been investigated. Laboratory tests were carried out on a number of square and rectangular model slabs. The supporting arrangement and the applied loading systems were the main variables. These experimental records were later compared with the numerical predictions. Some other test results from literature have been included also.