Ultimate Behavior of an R.C. Nuclear Containment Subjected to Internal Pressure and Earthquake

The results of nonlinear analysis of a reinforced concrete nuclear containment vessel subjected to dead load, internal pressure, and earthquake are presented. The membrane reinforcement for the containment is first designed based on the principle of minimum resistance using the stresses from an elastic analysis. The nonlinear analysis shows that the containment is able to achieve 102% of the design pressure and earthquake load along with its dead load. The objective of the research program involved is to understand and establish a relationship between the reinforcement design and the ultimate behavior of concrete shells. A nonlinear finite element program has been developed. The computer program includes a new concrete cracking model which is consistent with the limit state. The program also includes a new selective integration scheme which enables an accurate evaluation of the cracked element's stiffness matrix. Some of the initial cracking is due to the combined effect of hoop and shear stresses. As expected, these cracks are inclined at an angle less than 45° to the vertical. However, as more loading is applied and the cracking is spread wider, these and other cracks realine themselves to be closer to 45° to the vertical. The 45° orientation of the cracks allows for a more efficient resistance of combined direct and shear stresses by the reinforced concrete. It is found that the meridional and hoop reinforcements yield in the general areas predicted to be critical by the elastic analysis.