an orthotropic continuum model for the analysis of masonry structures

46 1995 TNO-95-NM-R07126. CONCLUSIONSAn anisotropic plane stress continuum model for the analysis of masonry structures has been presented.The model combines orthotropic elasticity with orthotropic plasticity. A composite yieldsurface that includes a Hill type yield criterion for compression and a Rankine type yield criterionfor tension has been developed. The model is novel in the sense that a relatively simple compositeyield surface is proposed and hardening and softening are included in a rational way. Modern plasticityconcepts as unconditionally stable implicit Euler backward return mappings, local Newton-Raphson iterative procedures and consistent tangent operators are used for all the modes of themodel. The performance of the implementation is assessed by means of single element tests. It isshown that the numerical algorithm is robust and numerically efÞcient.The model predicts different yield strengths and fracture energies along the material axes, both intension and compression. These features deÞne an extremely ßexible model capable of accommodatingthe behaviour obtained from experiments. The behaviour of the model is detailed by meansof single element tests, in which the response is evaluated upon different choices of the materialparameters. Unfortunately the number of test results of the composite material is relatively scarceand almost non-existent in the post-peak regime. The setup of experimental programs coordinatedby experimentalists and analysts seem therefore crucial.A comparison between numerical results and experimental results available is also included. Previousattempts to use macro-models, speciÞcally developed for masonry structures, included interfaceelements at the boundaries. The interface elements were responsible for most of the non-linear phenomenaobserved and, thus, only a poor validation of previously proposed macro-models exists. Itis shown that the model proposed in the present report is able to predict well the behaviour ofmasonry structures, with both ductile and brittle failure modes, as well as sufÞciently accurate collapseload values. However, this statement is only true if the structure is sufÞciently large that amacro-modelling strategy can be applied.