Fissuration thermomecanique des barrages en beton soumis aux variations saisonnieres de temperature en regions nordiques

In Quebec, many dams are subjected to seasonal temperature variations going up to 75°C. Under these conditions, concrete volumetric changes in the dam are often prevented. Therefore, thermal stresses or strains can develop in the concrete leading to the long term degradation of stiffness and strength of those dams. Moreover, seasonal thermal cycles lead to upstream-downstream movements that are often the source of horizontal and vertical crack propagation in dams.;In this study, a thermo-mechanical modeling procedure using the finite element method is proposed in order to assess the thermo-mechanical behavior of concrete structures including cracking. The computer programs ABAQUS and ANSYS are used in the study. Structural analyses and heat transfer were performed for a gravity dam (La Tuque 31 m) and an arch dam (arch 3-4 of the Daniel Johnson dam 214 m). The initial conditions and boundaries conditions as well as the input parameters are defined for the analyses. Equations to evaluate the mechanical properties (elastic modulus, tensile strength, compressive strength, fracture energy and Poisson's ratio) of concrete as a function of temperature are defined. The constitutive model of concrete used for thermo-mechanical analyses (fixed smeared crack model at Gauss points) and the assumptions of the finite element software used are presented.;A study was conducted to see a) the impact of varying the mechanical properties of a gravity dam with temperature and b) the effect of water penetration into cracks (seeping along lift joints), on computed stresses, displacements and cracking process. It is shown that the difference in stress between the analysis where mechanical properties vary with temperature and the one where properties remain constant is not significant (about 5%). However, this difference increases to 20% when looking at the computed displacements. The effect of the disintegration of the concrete surface exposed to ambient air on the safety factors (sliding, overturning and uplifting) has been studied for the gravity dam. It is shown that below a 2 m depth disintegration, all those safety factors are not significantly affected.;A study was performed on a section (arch 3-4, 89 m) of a multiple arch dam Daniel Johnson to quantify the flexibility provided by thermal oblique cracks located on the downstream face. The effect of cracking on stress distribution around the “plunging cracks” area has also been studied. To do this, linear analyzes considering a constant elastic modulus (analysis a) and a variable (isotropic) elastic modulus (analysis b) on the arch dam were made. Then, a nonlinear analysis (analysis c) using the ANSYS’s concrete element named "SOLID65"(fixed smeared crack for representative Gauss points concrete volume) was performed. The reinforcement steel was introduced near the downstream face of the arch dam to see its effect on the stress distribution (analysis d). Thermal stresses and displacements were evaluated at various pendulums present in the buttresses and the studied arch. Numerical cracks were compared with observed cracks obtained after drilling’s investigations. It is shown that there is a good correlation between the computed numerical cracks and the observed experimental ones. Also, the introduction of the reinforcing steel does not bring significant changes on the computed stresses and displacements. It is shown that there's a good correlation between analyses a), b), c) and d) regarding pendulums’ displacements.