Research On Temperature And Stress Of Prestressed Basement Superlong Concrete Structure

With the rapid development of modern economy and society,various regions have higher and higher requirements for multifunctional and comprehensive cities.In order to ensure the realization of building functions and the need for appearance and waterproof,super-long concrete basement structures are increasingly widely used in large commercial buildings and public buildings.Such structures often do not set expansion joints.The influence of temperature effect on the super-long concrete structure can not be ignored,because the temperature stress will lead to the temperature crack of the super-long concrete structure,which will affect the applicability and durability of the structure.The analysis of temperature stress and crack control is an important subject in the design and construction of super-long concrete structures,which needs to be studied in depth so as to meet the needs of designing larger area and larger size underground concrete structures.Taking the underground parking lot of the Comprehensive Transfer Service Center of Chengdu Jincheng Square as the research object,an analysis model of the structure is established.The shrinkage effect of concrete is converted into the equivalent temperature difference of concrete,which is superimposed with the reduction of temperature.The creep effect of concrete is reduced by introducing the stress relaxation coefficient to reduce the temperature drop.The finite element model of Midas/Gen was established to analyze the stress and deformation of the underground parking lot structure under the action of uniform cooling.The calculation and configuration of the prestressed tendons of the underground parking lot were carried out according to the second-level crack control standard,which provided reference for the design and construction of similar projects in the future.The main conclusions of this paper are as follows:（1）Temperature effect caused by temperature reduction has a significant influence on ultra-long concrete structures.The larger the temperature difference of cooling is,the greater the temperature stress and deformation will be in the ultra-long concrete structures.（2）In the research of temperature stress caused by seasonal temperature difference of super-long concrete structure,concrete shrinkage can be converted into concrete equivalent temperature difference and seasonal temperature difference for superposition calculation,and the creep of concrete can be reduced by stress relaxation coefficient.（3）Since the plate elements of the MIDAS/GEN model cannot apply prestress and lay out prestressed steel bundles,the same control effect can be achieved by applying concentrated loads on the nodes of the model to simulate prestress.（4）Comprehensive change to the service center in chengdu chengdu square plate structure of the underground parking garage in the temperature stress of prestressing can offset plate,thereby improving structural over＿length part to resist the ability of the temperature under the action of cracking,and unbonded prestressed channel friction small,construction is convenient,very suitable for the temperature stress in the structure control.（5）Based on the finite element analysis of the underground parking lot of Jincheng Square,it can be seen that the setting of the post-cast zone can effectively avoid the crack of the basement floor due to temperature stress in the early stage,and the closing time of the post-cast zone will affect the equivalent temperature difference of concrete shrinkage.