Triaxial concrete constitutive models and their application to the nonlinear analysis of nuclear plant structures

At the Los Alamos National Laboratory the finite element method has been used to predict the response of several types of concrete structures to severe accident conditions that could occur at nuclear power plants. Both prestressed and normally reinforced concrete structures have been analyzed to determine their responses to seismic events and quasistatic and dynamic pressure loads. Structures analyzed include concete containment buildings, prestressed concrete reactor vessels, and concrete shear walls. Finite element models of the structures have been developed with both the NONSAP-C and ADINA computer codes. Because the purpose of our analyses has generally been to determine failure loads and modes of failure, calculations are carried out well into the nonlinear range. Therefore, the computer codes have to include concrete constitutive models that treat concrete cracking and crushing and other nonlinear effects. In the paper we describe the concrete constitutive models and their application and discuss the shortcomings of the models in the structural simulations. We also discuss the numerical procedures used in our analyses and suggest some improvements that should make the analysis of concrete structures numerically stable to the point of failure. In several of the analyses presented, we compare computed response with measured response through at least the linear range. Our analysis of the shear wall response includes comparisons with test data to failure