Thermal Stress Analysis And Crack Control Of Cast-in-place Joint Of Assembled Bridge Pier

The connection of the bridge pier and cap is a key in the construction of assembled bridge pier.For the first time,a large number of assembled bridge piers with new pier-cap connection structure,which connects the assembled pier and the cap through the internal cast-in-place concrete,were used in a cross-sea bridge under construction.The temperature field formed by the hydration heat of internal cast-in-place concrete will cause large thermal stress on the surface of the precast pier,causing harmful cracks and affecting the serviceability of the bridge.Based on this background,thermal stress and crack control were studied in this paper.(1)The thermal stress and its influencing factors of the assembled bridge pier during connection with the cap were analyzed through numerical simulation.The effects of concrete temperature rise,concrete elastic modulus and wall thickness of prefabricated pier on the thermal stress were analyzed.The accuracy of the model was verified by comparison with field temperature data.The results show that cracks will occur on the surface of the assembled pier due to thermal stress without taking control measures.The main factor causing thermal stress is the thermal expansion of the internal cast-in-place concrete,and the secondary factor is the temperature gradient of the pier.When the concrete pouring temperature is increased from 10℃ to 40℃,the maximum tensile stress increases by 15.4%.The pier reinforcement can slightly increase the elastic modulus of concrete and reduce the thermal stress.The lateral load of concrete pouring has little effect on the stress of prefabricated pier.(2)The finite element model was used to analyze the single and combined measures of thermal stress control.Through the field tests of four combined measures,the effectiveness of the combined measures was verified.Based on the numerical analysis and field test results,a thermal stress control strategy was proposed and the field monitoring tests were carried out.As a single measure,the control effect of setting the thermal insulation buffer layer is the best,followed by the cooling water pipes,optimization of concrete proportion,layered construction and internal hole.The effect of outer insulation and inner cavity ventilation is poor.The recommended strategy includes optimized concrete proportion,cast concrete in three layers,in which the first layer and the second layer are respectively provided with a thermal insulation buffer layer and an internal hole.The field test shows that this scheme can effectively control the cracks and the thermal insulation buffer layer has a good barrier effect on the temperature transmission of the core-filled concrete to the precast pier.Besides,layered construction can effectively reduce the temperature peak and thermal stress.(3)Based on the theory of thermoelasticity,a simple calculation method for the thermal stress of assembled bridge pier was developed.By comparing with the finite element results,the calculation method was verified and the error was evaluated,and the corresponding correction coefficients were proposed.