| This project focuses on the high-strength bolt shear connectors(HBSC)in prefabricated composite beams as the research object.By combining high-strength bolts and highperformance concrete,a high-performance shear connector is formed to ensure the effective connection between the concrete slab and steel beam and to transfer longitudinal shear force.To explore the mechanical behavior of such high-performance shear connectors,finite element software is used to simulate the high-strength bolt shear connectors and analyze their shear performance and influencing factors.The main research work and conclusions include:(1)Summarizing and generalizing the research status of high-performance shear connectors used in prefabricated composite beams,establishing finite element models based on preliminary exploratory single-sided push-out tests for high-strength bolt shear connectors,and comparing the load-displacement curves and failure modes obtained from the simulation with experimental results to verify the accuracy and reliability of the model.Through in-depth analysis of 12 verified finite element models,the stress states and their variation processes of high-strength bolt shear connectors under different loading stages are obtained,and the force transmission path of the high-strength bolt shear connector is preliminarily obtained.Based on the load-displacement curve and stress cloud diagram of the model,the shear performance of R-type,RB-type,and RBN-type bolt shear connectors are compared,and the analysis shows that the RBN-type bolt shear connector model,with the steel pad increasing the contact area with the concrete,results in a more uniform stress distribution in the concrete and better shear performance.(2)Based on the verified finite element models,24 models are established for parameter analysis to analyze the effects of the flange thickness of the steel beam and the bolt diameter on the shear performance of high-strength bolt shear connectors.Another failure mode,hole wall pressure failure,is obtained except for concrete failure and bolt shear failure.The minimum thickness required for the high-strength bolt shear connector to avoid hole wall pressure failure is obtained.The parameter analysis results show that the obtained minimum thickness is more conservative than the thickness of the steel plate used in the existing experimental studies and the thickness calculated based on the specification formula.The simulation-based thickness is smaller and can save steel usage.(3)To avoid the occurrence of wall-bearing failure and reduce the thickness of the steel beam flange,thereby achieving the effect of saving steel,this study proposes a new type of high-strength bolt shear connection with an expanded-hole nut.By introducing the expandedhole nut to increase the bearing area of the wall,the bearing capacity of the wall under compression is improved.Finite element simulation analysis was carried out on the highstrength bolt shear connection with the expanded-hole nut,and three models with wall-bearing failure were introduced.The results show that the expanded-hole nut can effectively prevent wall-bearing failure,and the shear bearing capacity of the high-strength bolt shear connection with the expanded-hole nut is significantly improved.Compared with the results of the unilaterally pushed-out test model that has been verified,the thickness of the steel beam flange can be designed to be smaller while ensuring the shear bearing capacity.To further optimize the design of the expanded-hole nut,a parameter analysis of the thickness of the circular tube of the expanded-hole nut was carried out to determine the thickness of the circular tube that matches the diameter of the high-strength bolt shear connection,and the construction measures of the expanded-hole nut were improved.(4)To comprehensively analyze the stress situation of the high-strength bolt shear connection,a standard pushed-out test piece was designed based on the European standard EC4,and a finite element model was established.The simulation results were compared with the results of the unilaterally pushed-out test,verifying the reliability and effectiveness of the standard pushed-out test model.The results show that the size of the standard pushed-out test piece designed in this study is reasonable and feasible and can be applied in the experimental research of this type of high-strength bolt shear connection.Combined with the simulation results of the unilaterally pushed-out test,the complete force transmission path and stress state of the high-strength bolt shear connection in different stages were obtained.In addition,based on the standard pushed-out test model,parameter analysis was carried out on the shape and size of the reserved hole in the precast concrete slab,and the effect of the reserved hole on the shear performance of the high-strength bolt shear connection was obtained.The results show that the wedge-shaped reserved hole exhibits better initial stiffness,and the size of the reserved hole has no effect on the concrete damage within a certain range.The simulated key results can provide a certain reference for subsequent standard pushed-out test research. |
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