| Prefabricated assembled bent caps have been popularized and applied in recent years.The mechanical properties of the joints are the key factors affecting the overall mechanical properties of prefabricated bent caps.At present,the application of the dry shear key joints to large cantilever prefabricated bent caps has the following problems: 1)Lack of research on the shear performance of large shear key joints;2)The calculation formula of the shear bearing capacity lack of depth-to-height ratio,prestressed reinforcement ratio and other parameters;3)The shear bearing capacity of the shear key joint under the action of bending moment is lacking research.Based on the problems,this paper conducts research from three aspects: 1)Theoretical analysis of the shear resistance of key joints;2)An experimental study on the direct shear performance of large key teeth dry seams;3)Combined with finite element parameter analysis,a formula for calculating the shear bearing capacity of key joints considering the prestressed reinforcement ratio is proposed.(1)Theoretical analysis of the shear performance of dry key joints was carried out.A formula for calculating the shear bearing capacity of the dry key joints,which takes into account the material,the depth-to-height ratio,and the reinforcement ratio(stiffness)of the prestressed reinforcement,is proposed.This formula shows that the reinforcement ratio of the prestressed tendons and the depthto-height ratio of the key have an influence on the shear resistance of the key joint.(2)An experimental study on the shear performance of large key dry joints was carried out.The effects of key base height,key depth-to-height ratio,prestressed reinforcement ratio and key number on the shear performance of key joints were studied.The test results show that increasing the base height of the key or increasing the depth-to-height ratio of the key can improve the shear bearing capacity.For shear performance of the joints,it is better to use a large key with a base height of400 mm than using multiple small key with a base height of 200 mm.Different depth-to-height ratios of key will change the failure mode of the key joints.When the depth-to-height ratio of the key is0.233,the relative slippage of the key joints occurs due to insufficient friction.Increasing the reinforcement ratio of prestressed tendons can improve the shear bearing capacity and stiffness level of the dry key joint.Under the condition of the actual prestressed reinforcement ratio of the large cantilever bent cap,the dry shear key joint shear capacity calculation formula proposed by AASHTO will far overestimate the joint shear performance and the test results show that increasing the reinforcement ratio of the prestressed tendons can improve the shear resistance and stiffness level of the dry key joints.(3)A design method for shear resistance of dry joints with large key of large cantilever segment assembled bent cap is proposed.The finite element model of 18 dry key joints with different reinforcement ratios is parametrically analyzed,and the corresponding relationship between the reinforcement ratio and the shear bearing capacity of dry key joints is obtained.Based on the AASTHO formula and parameter analysis results,a formula for calculating the shear capacity of the dry key joint considering the reinforcement ratio is proposed.Through the above research,the relationship between the shear performance of the dry key joint and the key depth-to-height ratio,the prestressed reinforcement ratio at the joint,and the key depth is obtained,and through the experimental study,the superiority of setting large key at the joint of the large cantilever bent cap is clarified.Then,based on the test and finite element results,a design method for the shear capacity of the dry key joint considering the reinforcement ratio and the bending moment is proposed,which provides a certain experimental and theoretical basis for the application of large dry key joints to segment bent cap. |
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