Flexural Behavior Of U-bar Overlap Joint In Prefabricated Side Wall Of Metro Station Entrance

In order to achieve the strategic goal of carbon peak,carbon neutral,China vigorously promotes the development of assembled construction.Assembled subway station has outstanding advantages such as low labor consumption,high efficiency,reliable quality,small noise pollution and environmental protection.In order to make the connection of assembled entrance of metro station easy and reliable,the prefabricated side walls are connected by U-bar overlap joint,and the most unfavorable bending side wall bottom connection node was selected for bending study.At present,the lap connection is rarely researched,and force transferring mechanism of U-bar overlap joint is complex,and lap length is not clearly given,which limits the promotion and application of this new connection.Therefore,based on a subway station project in Xi’an,through full-scale test,finite element simulation and theoretical analysis,the flexural properties of joint in prefabricated side wall of metro station entrance was studied in this paper:(1)The flexural behavior of two full-scale specimens of U-bar overlap joint nodes was designed and tested to study the crack development,damage process and form,characteristic load and strain change law of U-bar in the lap joint area under bending load.The test results show that the flexural failure process of U-bar overlap joints is similar to that of normal reinforced concrete beam,which can be divided into elastic stage,cracking to yield stage and failure stage.Cracks first appear between the post-cast section and the precast section.In the final failure,the main cracks were distributed at the joints between the postcast section and the precast section,the concrete at the upper support was crushed,and the bottom of the U-bar overlap area was tensioned and yielded,resulting in the failure of the specimen.The specimen still has a certain bearing capacity after the steel bar yields,and the ductility of the specimen is good.(2)The finite element model of the U-bar overlap joint node specimen was established using the finite element software ABAQUS.Variable parameter analysis was performed on the model,and two groups of 16 U-bar overlap joint node specimens were designed and completed to simulate the flexural performance considering the parameters of lap length,slot size and shape of groove,and lap spacing of U-bar overlap joint.The analysis results show that: the load carrying capacity and stiffness of the specimen decreases with decreasing lap length,and the structural measures of the groove have a small effect on the failure pattern of the specimen,when reducing the width taking round shape of the groove and can alleviate the stress concentration phenomenon.The transverse groove can slow down the development trend of cracks and improve the flexural behavior.(3)The flexural capacity of U-bar overlap joint node specimens was theoretically analyzed.Based on the analysis of force transferring mechanism of U-bar overlap joint,the calculation model of flexural bearing capacity of U-bar overlap joint was modified and the calculation formula of flexural bearing capacity applicable to U-bar overlap joint was proposed,and the model was verified by the test results and collected test data.The crack width calculation model in the existing code is analyzed and amended.Based on the calculation formula of flexural bearing capacity,design suggestions of lap length for U-bar overlap connection under bending load were proposed.In this paper,the flexural properties of assembled U-bar overlap joint nodes was studied,the calculation formulas of flexural bearing capacity and crack width were revised,and design suggestions for U-bar overlap joint nodes were proposed.It provides theoretical support for the engineering application and promotion of such assembled connections.