Experimental And Theoretical Research On Shear Behavior Of Joints In Precast Segmental Bridges About High-speed Railway

Precast segmental bridges have the advantages of rapid construction speed,little effects on surrounding traffic,easily controlling in quality,wide span adaptability,good durability and low life-cycle cost,etc.Joints are the special structure and the weak parts of precast segmental bridges.The mechanical behaviour of which has a vital impact on the serviceability limit state and the ultimate limit state of precast segmental bridges.However,there is no unified understanding of the stress behavior and shear capacity calculation of joints in existing research.In order to study the shear behavior of keyed joints,10 groups of structural specimens with concrete strength of C60 are designed to complete shear tests,focusing on the mechanical behavior of keyed joints under four parameters(bond type of joint,lateral stress level,structure of keyed joints,addition of steel fiber).The objectives of research include cracking load,ultimate shear load,crack development process,failure mode and relative slip of specimens,etc.The finite element method is used to establish the numerical model under each parameter,and the results are compared with the test results to analyze the parameters affecting on the shear capacity.Then,the formulas for calculating the shear capacity of keyed joints studied by some scholars at domestic and foreign are checked and evaluated by using the test parameters of the specimens in this paper,and the revised formulas are put forward.The main conclusions are as follows.(1)Four kinds of test parameters have different effects on the shear capacity of keyed joints.Different types of bonding between joints directly affect the crack development and shear bearing capacity of structural specimens.The epoxid joint members is brittle,but the ultimate shear bearing capacity of bonded members is obviously better than that of dry joint members which are under the same parameters.The lateral stress level has a great influence on the shear bearing capacity of the keyed joints.With the increase of the normal stress,the shear bearing capacity of the key teeth structure increases.The type of keys also has a great influence on the shear bearing capacity of joint structure.The mechanical properties of reinforced large keyed joints are the most superior,followed by non-reinforced large keyed joints and multiple small keyed joints.The addition of steel fibers has no obvious effect on improving the shear bearing capacity of keyed joints,but it delays the cracking and improves the brittle failure characteristics to a certain extent.The residual load ofreinforced large keys specimens is relatively maximum after failure,which indicates that this kind of keyed structure has safer bearing capacity after failure.(2)The main failure mode of components under loading is the direct shear failure of keys.Among them,the structural cracks with dry-jointed keys are gradually developing.For dry-jointed multi-keys components,the keys are sheared one by one from bottom to top.While the structural cracks of epoxid-jointed keys occur suddenly,and the epoxid-jointed multi-keys are sheared almost at the same time.(3)After statistic and evaluation of some formulas for calculating shear bearing capacity,it is found that the calculation results of Zhang Jiwen's suggested formulas are in good agreement with the test results.The average underestimation of dry-joint structures is 6%,while overestimation of epoxid-joint structures is also 6%.Liu Zhao's suggested formula takes second place.AASHTO formula is more suitable for dry-joint structures in this test,while overestimates the bearing capacity of epoxid-joint structures.(4)There is no explicit formula for calculating shear capacity of reinforced large keys specimens.Based on the analysis of the test results,It is suggested that the magnification factor can be multiplied on the calculation of the same size large keys without reinforcement..The magnification coefficients of dry-joint and epoxid-joint structures are 1.05 and 1.10,respectively.(5)Summarizing the test parameters about ordinary concrete keyed joint specimens of some domestic teams and this test.On the basis of Zhang Jiwen's formula,the coefficient of the formula is revised,and the formula for calculating shear capacity of keyed joints with higher fitting degree is obtained.