The. Concrete Pier Structure Thermal Stress Analysis And Its Applications

The bulk of the concrete piers in the hydrotechnics is rather large, though the resist-resisting intension of the concrete is rather low, the heat conduction capability of is bad and the distortion caused by temperature change is restricted, the cracks usually appear in the concrete piers during the constructing or using period. These cracks destroy the construction integrality of the piers and affect the structure security and endurance. The research aiming at temperature control and avoiding cracking of the mass concrete mainly focus on temperature control and avoiding cracking of the dam whether domestic or overseas, and large numbers of the research have attained harvest in a certain extent. But the research to such massif concrete construction as the piers is scarce, thus it is hard to avoid that cracks frequently happen in the piers. Up to now, temperature control and avoiding cracking questions of pier concrete are still the great problems imminently need to solve in hydrotechnics and civil engineering fields.Concrete intension and strain is one of the main factors which influences the thermal cracks of the concrete. Cracks appear in the yangjialing unusual spillway piers of Zhaopingtai reservoir in the replacing period. Different levels of the thermal cracks of the concrete occur in almost all piers that have been placed during the period which age is from 7 days to 28 days. The main reason that causes pier concrete thermal cracks to occur is that thermal stress exceeds the resist-resisting intension of the concrete or the thermal strain of the concrete exceeds the ultimate pulling and stretching value.It gets the elastic modulus and the resist-resisting intension of the concrete through the mechanical behavior trial study and analysis to the yangjialing unusual spillway piers of Zhaopingtai reservoir. It gets atmosphere temperature curves and the temperature curves of the model points inside the piers which vary with the concrete age through analyzing the related measured temperature data. The 3-D mesh method is used to analyze the transient temperature field and temperature stress of the piers during placement. The variations of elastic modulus, creep, hydration and atmosphere temperature variation related to the age of concrete and the effect of layered placement (using killing and reactiving elements to realize layered placement) are taken into account. Through contrasting the simulated results and real measured temperature data, the main cause of thermal cracks is analyzed and it lies in the rising and decreasing of inner temperatures is too fast and atmosphere temperaturelowers suddenly.Using the fracture mechanics method it analyzes the stability of crack development after the crazes occur in the pier concrete, predicts the possible development trend of the cracks and evaluates its harm. Finally measures for avoiding the pier concrete cracking and dwindling thermal stress are given from the three points of controlling temperature, improving constraint condition and increasing the concrete performance of resisting cracking through considering the factors which influence the thermal cracks of the pier concrete. Methods for restricting, repairing and reinforcing the thermal cracks in the pier concrete are put forward.