Study On Seismic Performance Of Multiplanar KK-Joints In Trussed Concrete-Filled Steel Tubular Hybrid Structures

Trussed concrete-filled steel tubular(CFST)hybrid structures have the characteristics of high strength,large spatial stiffness,and strong integrity.It is being used in constructions in earthquake-prone regions.The multiplanar KK-joint composed of a CFST chord and four hollow steel tube webs,which is one of the most widely used joint forms in trussed CFST hybrid structures.However,there is currently a lack of relevant research on the seismic performance of this type of joints,and key issues such as the mechanical performance of the multiplanar KK-joint,as well as the "hybrid effects" between chords and webs need to be further explored.The main research work and outcomes of this thesis are as follows:1.Lateral local loading tests were carried out on 24 CFST chords and 2 hollow steel tube chords.The effects of various parameters on the behavior of the lateral local loaded chord were explored,including the chord type,the loading rod type,material parameters,geometric parameters,etc.The finite element(FE)model of the bidirectional lateral local loaded CFST chord was established,and the load transfer mechanism was clarified.The influence of key parameters such as the strength of steel and concrete,the diameter to thickness ratio of chord steel tube,and the ratio of the rod diameter to the chord diameter on the resistance of the chord to lateral local bearing was studied.A calculation method for the resistance of chord subjected to bidirectional lateral compression was proposed.2.Experimental investigations were conducted on 13 multiplanar KK-joints in trussed CFST hybrid structures,1 planar K-joint,and 1 hollow steel tube multiplanar KKjoint under seismic loading.The main test parameters included the joint type,the crosssectional type,steel strength,the replacement ratio of recycled coarse aggregate,the web size,the long-term load effect and the axial load level of chord.The whole loading process,failure modes and hot spot stress distribution of the joints were analyzed.Studies were conducted to find out the influence of relevant parameters on the seismic performance of joints such as strength,stiffness,ductility and energy dissipation capacity,and the distribution of hot spot stress in the joint region was also explored.3.A nonlinear FE model of multiplanar KK-joints in trussed CFST hybrid structures under seismic loading was established.The model considered the effects of long-term load,initial geometric defects and boundary conditions.The calculated results of the model were in good agreement with the experimental data,indicating that the model had high precision and accuracy.The mechanical behavior and working mechanism of the joints under seismic loading were analyzed.The influence of multiplanar coupling effect was explored.The composite effects among materials and hybrid effects among members were clarified.The parametric analysis was carried out,and effects of key factors affecting the seismic performance of the joints were clarified.4.Based on the FE model and parametric analysis results,a calculation method for the resistance and a hysteretic relation model of multiplanar KK-joints in trussed CFST hybrid structures were proposed.By comparing with the test data and the calculation results of the FE model,the accuracy of the calculation method and the model was verified.The calculation method of "hybrid effect coefficient" was proposed,providing a quantitative index for describing the hybrid effects between chords and webs.Relevant design suggestions for joint details were put forward for CFST KK-joints.