Research On Mechanical Behavior Of Concrete Filled Steel Tubular Column-steel Beam Blind Bolted Joints

Concrete filled steel tubular column-steel beam blind bolted joints have the advantages of good seismic performance,convenient onstruction and economical,therefore it has good application prospect in engineering.In this thesis,the experimental study,numerical simulation and theoretical analysis of the blind bolted joints are carried out.The main research work and conclusions are summarized as follows:(1)Eight concrete filled steel tubular column-steel beam bolted joints were tested under axial tension and bending-shear loading,and the influences of structural measures and bolts types on the integrity of the core area of the joint were investigated.The results show that,the working performance of blind bolt is stable and reliable;The binding bars are beneficial to improve integrity of the core area of square joints,however,the stress concentration of the welding seam is easy to cause the fracture;Blind bolted connections have favorable ability of rotation.(2)The influence of different structural measures on the seismic performance of the joints is analyzed by the test of six square CFST column-steel beam blind bolted joints.The key seismic performance indexes of the joints are studied by analyzing the flexural bearing capacity,strength degradation,stiffness degradation,ductility and energy dissipation.Experimental results show that the joint has good ductility,and the seismic code is satisfied;The core zone of the joint welding outer channels or installing short H-beam can significantly improve the flexural bearing capacity,initial rotation stiffness,ductility and energy dissipation,therefor,the seismic performance of the joints have been significantly enhanced;Based on the analysis of the moment-rotation skeleton curve of the joints,the blind bolted joints can be classified as semi-rigid and partially connecting with the EC3 criterion.(3)Finite element models of monotonic loading and cyclic loading of blind bolted joints were established by using ABAQUS software.The finite element model considering the material nonlinearity,geometric nonlinearity and boundary nonlinearity.The reliability and generality of the finite element model are verified by comparing the calculated results with the typical test results.(4)Static loading numerical simulation is carried out for blind bolted joints and strengthened joints.The influence of each parameter on the moment-rotation curve and the failure mode of the joint is discussed in detail.Through the parameters analysis,the mechanical properties of the blind bolted joints are similar to penetration bolt joints when the joint is strengthened.(5)Based on the component method,a three parameters simplified model is presented for calculating the moment-rotation curves of blind bolted joint.The model is simple and the physical meaning is clear,and the calculation results are in good agreement with the experimental results,which can provide reference for engineering practice.