Simulation of the thermal stress in mass concrete by thermal stress measuring device

Abstract

Mass concrete generates internal heat during the hydration period that occurs soon after casting. Added to these internal heat changes are the environmental conditions that the structure is subjected to during its designed life. These thermal changes in the material affect the elastic and creep properties of the material and in turn, the stress fields within the structure. This thermal stress problem is commonly understood as an initial defect of structure and needs special attention of an engineer to make sure of safety and stability of the structure. The thermal stress depends on the structural shape and the constraint conditions, and cracks usually develop from tensile stresses which result from a temperature drop. However, in this dissertation, application of various degree of constraint in the thermal stress device is verified and for this purpose a series of experiments were performed on mass concrete followed by numerical simulation, so conditions like they occur in concrete structures could be simulated realistically. The application of various degrees of constraint can be achieved by using constraint frame material with different thermal expansion coefficient, length, and cross sectional area. The device is located in a temperature and humidity control chamber that follows the temperature history, which has been previously obtained from temperature distribution analysis, thus simulating the temperature development in the real structure. Further, the influence of non-thermal deformation due to shrinkage could be avoid controlling humidity in the chamber and wrapping of specimen surfaces with any appropriate water proofing polythene sheet. For the continuous measurement of the thermal strains, load cell in the device has been replaced by strain gages to define the restraint of the device in a more accurate fashion. The results from experiments show that the thermal stresses estimated from simulation agree well with the general stress variations in the re...