Study On Seismic Behavior Of A Blind Bolted Connection Joint Between Modules In Modular Steel Frame

In recent years,China’s level of industrialization in construction has rapidly increased.Modular buildings,as representatives of industrialized building structures,have introduced many new types of joints.The"four columns and sixteen beams"joint of modular building structures not only imposes high technical requirements on the installation of the structure but also has a significant impact on the mechanical properties of the structure,particularly seismic performance.This article describes a blind bolted connection joint between modules and analyzes the advantages of this type of joint in installation.By using a combination of experimental,finite element analysis,and theoretical analysis methods,the article studies the seismic performance of this joint in a single-frame structure.The research results can provide a reference for the design of similar joints and a basis for the promotion and application of this joint.（1）Three full-scale specimens of blind bolted connection joints between modules were designed,and low-cycle reciprocating loading tests were conducted to study the failure mode,bending moment-rotation curve,hysteresis performance,energy dissipation capacity,and component deformation characteristics of the joint specimens.The test results show that the hysteresis curve of the specimen is relatively full,with maximum equivalent viscous damping coefficients of 0.411,0.232,and 0.355 for the three joints,respectively,which have strong energy dissipation capacity.The ductility coefficient of the three specimens is greater than 3.00,and the ultimate interlayer displacement angles are greater than 7%,meeting the steel structure design standard’s limit of 4%for interlayer displacement angle during frequent earthquakes.The joint zone diaphragms have a significant impact on the seismic performance of the joint,and the specimen without joint zone diaphragms experiences a brittle failure of the beam end weld tearing.After adding cover plates to the beam end,the joint’s strength and stiffness were significantly improved,and it has a high energy dissipation potential.The blind bolted connection joint has strong rotational performance,and increasing the connection plate thickness can increase the initial stiffness of the joint,but the effect is not significant.（2）Using the finite element analysis software ABAQUS,the finite element model of the three specimens in the test was established,and the optimal modeling method was explored through comparison with the test data.The comparison of finite element contour maps,hysteresis curves,and initial stiffness shows that the numerical calculation results of finite element analysis are generally consistent with the test results,verifying the effectiveness of the finite element numerical analysis method and providing a basis for subsequent parameter analysis of the seismic performance of the blind bolted connection joints using finite element models.（3）A nonlinear finite element numerical model of the blind bolted connection joint between modules was established based on parameters such as connection plate thickness,unidirectional high-strength bolt grade,and the number of unidirectional high-strength bolts.Low-cycle reciprocating loads were applied to the joint model through finite element numerical analysis,and the effect of different parameters on the seismic performance of the joint was studied from the aspects of the model’s failure mode,hysteresis curve,skeleton curve,and equivalent viscous damping coefficient.The results show that changing the connection plate thickness,unidirectional high-strength bolt grade,and the number of unidirectional high-strength bolts has little impact on the seismic performance of the joint.Increasing the thickness of the horizontal connecting plate can significantly reduce the rate of deformation increase during the elastic stage and also significantly reduce the maximum deformation during the plastic stage.Changing the grade and quantity of bolts has no significant effect on the deformation of the horizontal connecting plate during either the elastic or plastic stages.（4）A combined approach of theoretical analysis and experimental data was used to investigate the stress and stiffness of the horizontal connecting plate at the blind bolted connection joint between modules.The results show that the horizontal connecting plate can be divided into two regions:the region ₀L inside the module column and the region ₁L between columns.The deformation of the horizontal connecting plate is mainly caused by the misalignment deformation at both ends of the ₁L region.The restraint of the module columns on the region of the horizontal connecting plate is between fixed supports and hinged supports.The stress of the connecting plate is mainly related to the thickness of the module column wall,the length and thickness of the connecting plate,and the misalignment of the region ₁L.When designing a specific joint,the thickness of the module column wall and the length of the connecting plate is already determined,so the calculation of the load-bearing capacity of the connecting plate mainly considers the thickness of the connecting plate and the misalignment of the region.