Elastic Strength Diagnosis of the Dez Concrete Arch Dam Using Thermal Inverse Analysis

Abstract

Strength degradation of mass concrete of the Dez concrete arch dam was evaluated using inverse analysis methods. A three-dimensional nonlinear finite element model (FEM) was developed here for such an evaluation by considering the effect of interaction between vertical adjacent blocks of the dam. The special attention was paid to the thermal loads. The Young’s modulus and Poisson’s ratio and thermal expansion coefficient of mass concrete of the dam were selected as variable indices for monitoring the strength degradation of dam concrete in the proposed model. An iterative solution scheme was performed to determine the mentioned indices in such a way that a predefined error function would be minimized. An error function has been considered as the sum of the squares of the errors in the nodes of the mesh. An error in a node was defined as the difference between computed displacement vector based on the developed model and the recorded displacement vector with the instruments located in the dam body. The sequences of the solution method have been presented in the paper. The unique characteristic of the suggested method is the contribution of thermal loads in the inverse analysis. The obtained results indicated that the mass concrete of the dam has experienced approximately 34% reduction in its initial elastic modulus, 15% enlargement in its initial Poisson’s ratio, and 25% reduction in its initial thermal expansion coefficient during its 42-year life period (1965–2007). According to the fundamentals of theory of elasticity, it is concluded that the failure surface (the eigenvalues of elastic tensor establish a failure surface for concrete in stress space) of the concrete material of the Dez dam has been contracted significantly. This reduction is strongly thought to be attributable to aggressive hygro-thermo-mechanical effects on downstream parts and may be the result of hygo-thermo-chemo (namely calcium leaching)-mechanical effects at upstream parts of the dam based on similar evidence recorded in the scientific research.