Investigation On Mechanical Performance Of Stainless Steel High Strength Bolted Connections And Joints

In recent years,with the advancement of the “Belt and Road” initiative and “Marine Strategy”,problems of structural corrosion have become increasingly prominent.Stainless steel is the best solution for the structural durability,safety and economy problem in a highly corrosive environment.However,current researches are focusing on the material and member level,while the stainless steel connections and joints have gained less attention.Based on the background above,this paper starts with high-performance connection research and adopts parametric modeling method to study the stainless steel high strength bolted connections and end-plate connections in the following three aspects:(1)In the aspect of research and development of high slip factors: slip factors of 10 groups(a total of 59)of stainless steel and carbon steel specimens were tested.Besides,roughness test,3D surface observation and hardness test were also carried out.Traditional carbon steel surface treatment methods(sand blasting and shot blasting),improved surface treatment methods(clamping rubber pad,copper plate and aluminum plate),and novel surface treatment methods(powder spraying,deep drawing and mechanical drawing)were studied in depth.Traditional surface treatment methods were proved to produce a slip factor lower than 0.2 on stainless steel surface,while mechanical drawing and powder spraying could make a high slip factor.Surface treatment methods suitable for stainless steel were proposed and the direction for further improvement of the frictional surface treatment was pointed out based on the 3D height parameters.The key factors affecting the slip factor of stainless steel frictional surface were explored and analyzed to determine the approximate positive correlation between the roughness,real contact area and slip factor.Finally,the design method of stainless steel high strength bolted frictional connection was improved.(2)In the aspect of parametric analysis of mechanical properties of stainless steel high strength bolted end-plate connections: the ABAQUS kernel script was created based on Python to realize the parametric modeling of the high strength bolted end-plate connections,so as to ensure the efficiency and inheritance of complex modeling.In addition,by comparing with the static test results of carbon steel joints,the accuracy of the finite element analysis method was verified.The finite element analysis of the static mechanical performance of 12 high strength bolted end-plate connections was carried out.The influence of the end plate thickness,end plate stiffener,bolt diameter,column web thickness and slip factor on the initial rotation stiffness,design moment capacity,ultimate moment capacity,ultimate rotation and the failure mode of the connection was investigated.The similarities and differences of austenitic stainless steel,duplex stainless steel and carbon steel in the performance of high strength bolted end-plate connections were conceptually discussed,which laid the foundation for subsequent theoretical analysis.(3)In the aspect of the moment-rotation relationship of the stainless steel high strength bolted endplate connection: according to the nonlinear characteristics of moment-rotation curve of stainless steel connection and based on the “integral component method + local fitting method”,a bending moment-rotation curve in the form of Ramberg-Osgood formula was established including the initial rotation stiffness,yield bending moment,yield rotation angle,ultimate bending moment and ultimate rotation angle.Based on the analysis results of the bolted plate sub-model,the calculation expressions of yield load,yield deformation,ultimate load and ultimate deformation of the T-shaped connector were put forward,with the ratio of the connecting plate bending stiffness to the bolt axial stiffness as the parameter,so that the complex pry action problem in the end plate and column flange plate mechanical performance was solved.the calculation of the initial stiffness of the connection was improved by considering the shear stiffness of the shear domain and the lateral stiffness of the column flange plate around the domain.By introducing the bolted plate sub-model method,the calculation of the connection yield moment was improved,and the ultimate bending moment of the connection based on the bolt failure was established.The expressions of the connection yield rotation angle and ultimate rotation angle were established by considering the shear nonlinearity of the material in the connection domain.Compared with the finite element analysis,the moment-rotation curves put forward in this paper have shown a good agreement.The research results of this paper provide an experimental and theoretical basis for the revision of“Technical Specification for Stainless Steel Structures”(CECS410: 2015),which benefits the promotion of stainless steel structures application.