Stress Analysis On Hydraulic Concrete Based On Coupled Heat-Moisture Transfer

Avoidance of cracking damage due to temperature and shrinkage is an important objective in the design of dam. The phenomenon of concrete shrinkage is complex which is still far from being fully understood. Moreover, shrinkage has been omitted for a long time and there're only some empirical formulations in use. Temperature load simulation has made a major success in past two decades. However, the impact of humidity on heat conduction has not been considered. It still needs to be improved.As a matter of fact, heat and moisture transfer are combined. This interaction should be taken into account when analyzing their stress. In this thesis, an equation by Kemeng Bao[15] for coupled heat-moisture conduction has been introduced, which laid the foundation of next step of structural analysis since more precise field of temperature and moisture could be gotten. According to the research progress at home and abroad, some basic physical mechanisms have been proposed to explain the phenomenon of drying shrinkage and suggest some profitable models and applications. Based on the theory of capillary and disjoining pressure, an improved shrinkage model has been established. Aging material model and autogenous shrinkage due to self-desiccation are expressed as functions of hydration degree. Some parameters used in model are given in form of fitting. A FEM computer program has been developed for the numerical solution of structural analysis. A numerical example is given as a validation of the model of shrinkage using published results of the experimental study and numerical results which have got common agreement. Then, based on this program several numerical examples are performed to study the characteristic behavior of drying shrinkage and temperature deformation, so does their interaction. Finally, there performs an example to study the effect of insulating layer in cold wave by changing the boundary parameters in heat-mass coupled model.Based on the above work, the following conclusions have been gotten. First, humidity transfer processes slowly, and it takes 40 days to come to the transfer balance in the 50% relative humidity drying environment. The shrinkage stress gradient is intensive, mainly concentrating in the surface. The stress due to shrinkage can reach the limit of concrete tensile strength when suffered a continuously drying condition. Secondly, temperature conduction processes relatively quickly and can impacts a few meters deep. Temperature drop of 10-degree can result in 60 micro-strain in 10 days and stress can reach 1.4MPa. Thirdly, there is a significant difference of moisture transfer with different temperature, which also affects the field of shrinkage and stress. However, it makes no difference of heat transfer under different relative humidity environment. It proves that humidity affects heat field mainly by moisture transfer which bring away the heat. Finally, early concrete and the dam in temperature and moisture heavily changing region should strengthen the moisture and heat conversation.