Design Method For Joints Between CFST Columns And Steel Beams Connected With Blind Bolts

Concrete filled steel tubular(CFST)columns were widely used in building structures due to their advantages such as high ultimate bearing capacity,good earthquake resistance and fire resistance.The connection between concrete filled steel tubular columns and steel beams were often welded.However,The welding joint is prone to brittle failure,so using the bolted end plate connection can avoid the problem.Considering the closed section of steel tube,it was difficult to use the traditional high-strength bolts.The use of blind bolts instead of high-strength bolts can solve the problem in the closed section.At present,some experimental study on the connection between concrete filled steel tubular columns and steel beams connected with blinds have been carried out.In order to popularize and apply these joints to practical engineering,it is necessary to study the theoretical design method.In this paper,the theoretical analysis and numerical simulation method were used to study the initial rotational stiffness,ultimate bearing capacity,moment rotation relationship curves and the design method of joints connected with blind bolts,the major research work and outcome were summarized in the followings:(1)The component method was used to calculate the initial rotational stiffness of the joints.through analyzing the influence of each component on the stiffness and deformation characteristics,The calculation model of each component was established.After calculating the corresponding stiffness,The whole initial rotational stiffness can be integrated.The comparison between the model and experimental results showed that the model was rational and more accurate.Moreover,the calculation process of the model was convenient.(2)The single factor analysis method was used to determine the ultimate bearing capacity of the joints.The possible failure modes including the damage of bolts,the failure of end plate,the damage of steel tube wall and the yield failure of beam were analyzed.The simplified calculation formula of each component was deduced,which was validated by a comparison with the experimental data.(3)By a comparative analysis of all kinds of moment-rotation relationship models,three parameters model was selected to describe the moment-rotation relationship.The model mainly contains three parameters:the initial rotational stiffness,the ultimate bearing capacity,the shape parameters.After getting the initial rotational stiffness and the ultimate bearing capacity by the second and third chapter,the shape parameter could be concluded by fitting the existing finite element data,The results of comparison showed that the model can better describe the moment-rotation relationship curve.(4)The ABAQUS was used to establish the finite element analysis models with a similar loading system,The validity of the model were verified by comparing with experimental data;a typical specimen was selected to make a detailed analysis such as the work mechanism and the deformation modes.what's more,An ideal failure mode was selected by summarizing the previous experimental test,Which can give reference for joints design.(5)Based on the above research and combined with the relevant specifications,this paper put forward the design method of rigid connections.Finally,the validity of the design method was verified by the finite element method,which can provide a reference for engineering.