Napjatost základových konstrukcí vlivem smršťování betonu

Abstract

The main subject of the dissertation of the thesis is the issue of deformation and subsequent stress of foundation reinforced concrete structures caused by volume changes of concrete. Volume changes of concrete mainly include shrinkage of concrete due to binder hydration, but also include the swelling of concrete in the initial stages of curing and the effect of long-term climatic conditions such as temperature and relative humidity of air. This is general description of the processes that the concrete structure has been going through for a long time, regardless of the external load. Sliding joints located between the foundation joint and the foundation structure are elements that allow to reduce friction or shear stress. This shear stress can in principle occur in three different influences, which include volume changes of concrete (rheological properties, expansion due to temperature), prestressing of the concrete structure and the influence of the undermined area. The dissertation focuses on one of these influences, which are volume changes of the concrete structure due to shrinkage of concrete. The use of sliding joints is in the case of undermined area commonly used method, but in the case of the influence of volume changes or prestressing of concrete structure, it is an issue that is little researched and not sufficiently described. In the last few years, intensive research has been carried out within VSB-TU Ostrava focusing on the use of sliding joints in terms of design, material properties and in terms of technological implementation. The obtained results of the previous research are followed up in this dissertation. The set of experimental tests was performed, where the measurement of volume changes of various concretes and sliding joints was performed in a laboratory-controlled and outdoor environment. String strain gauges and a shrinkage trough were used to measure volume changes. The uniqueness of the experimental part lies mainly in the fact that the measurements were performed on large-scale samples in real conditions, considering practically usable materials. These obtained results were then used in computational models to calculate the shrinkage of concrete structures. The results of free shrinkage from all these rheological models differ significantly compared to the measured values, considering the effect of friction and the possible use of the sliding joint. In this context, free and bound shrinkage, and the influence of friction on the development of stress are also discussed. The results of the experimental part are subjected to analysis and comparison with prediction according to computational models with evaluation of possible differences. The aim of the dissertation is to describe the methodology for measuring volume changes in the interaction of a concrete structure and a sliding joint. Development of volume changes regarding the influence of specimen size and different measurement methods. Furthermore, evaluation and analysis of the results of the experimental part, which allow comparison in different conditions, and finally evaluation and comparison with predicted results from computational models. The resulting values from the computational models without considering friction and the results from the experimental part provide different results. This knowledge can further serve for further development of computational models and design of sliding joints with considering the volume changes of concrete.