A stress resultant plasticity model for the analysis of reinforced concrete shell and box structures

This paper concerns the development and implementation of an orthotropic, stress resultant elastoplastic finite-element model for the collapse load analysis of reinforced concrete shells and box beams. The model is based on the accepted rationale of yield line theory for reinforced concrete, with the essential approximations required to obtain closed-form solutions for the yield function for shells. The behaviour of these functions is studied, and modifications are introduced to ensure a robust finite-element model of complex cases involving six stress resultants (M-x, M-y, M-xy, N-x, N-y, N-xy). Onset of plasticity is always governed by the general yield-line model (YLM), but in some cases the stress-resultant form of a von Mises function is used post-yield to ensure the proper evolution of plastic strains. Case studies are presented, involving isotropic and orthotropic shells and boxes, to assess the behaviour of the yield-line approach. The YLM function is shown to perform extremely well, compared with experiment and analytical solutions, in predicting both the collapse loads and failure mechanisms.