Experimental Study On Shrinkage And Creep Of Long-span Steel Truss Stiffened Concrete Continuous Rigid Frame Bridge For High-speed Railway

Shrinkage and creep are one of the main causes of diseases such as continuous midspan deflection and prestress loss of concrete bridge structures.The correct analysis of shrinkage and creep is an important link that cannot be ignored in the whole process of design,construction and using of concrete bridges.The existing large number of shrinkage and creep models consider different factors and apply different conditions,so the calculation results vary greatly.Therefore,it is an important prerequisite for controlling calculation errors that select an appropriate shrinkage and creep model in the analysis of shrinkage and creep effects of practical engineering structure.In this dissertation,a long-span steel truss stiffened concrete continuous rigid frame bridge is taken as the engineering background,using the bridge analysis software Midas Civil to establish the finite element model of the whole bridge.Combined with the tests of concrete used in the main girder,the influence of shrinkage and creep on the stress and deformation of the main girder is analyzed.Besides,the influence of the stiffened steel truss on the deformation of the main girder is also analyzed.The main research contents and conclusions are as follows:（1）In order to analyze the mechanical properties of concrete used in the main girder,some experiments were designed to measure the cubic compressive strength,prism compressive strength and elastic modulus of concrete,whose loading age were 7^th day,14^thh day,21^th day,28^th day and 45^th day.The results show that the compressive strength can be expressed by GL2000 model and the elastic modulus can be expressed by CEB-FIP 90 model;（2）According to the actual situation of tensioning prestressing tendons after 7 days of concrete pouring during construction,a set of outdoor shrinkage and creep tests were designed.The creep loading age was 7^thh day and the stress level was 0.32.The results show that the creep develops rapidly in the first month,after one month,the creep rate decreases.And the creep has basically reached a stable level after 6 months of load holding;（3）The creep development function is fitted based on the creep test data for 6 months.The long-term creep value calculated by the fitting function is approximately considered as the creep test value,and is compared with the calculated values of several classical shrinkage and creep models.The results show that there are the least differences between the creep test results and the calculated results of AASHTO model.So the AASHTO model can be preferentially selected to analyze the shrinkage and creep effect of main girder.（4）The mid-span deflection of main girder is increased because of the shrinkage and creep.The maximum deflection of the main girder calculated by AASHTO model for 10years is 94.4%higher than that without considering the shrinkage and creep effect at the same position.While the stiffened steel trusses reduce the mid-span deflection of main girder.When there are steel trusses on deck of main girder,the maximum deflection is reduced by17.8%under all dead loads.