| The concrete-filled steel tubular(CFST)columns are widely used in practice due to their superior performance under external loads.One important issue in the application of CFST columns in framed structures is the beam-to-column connection.The beam-to-column connection is mostly the internal-diaphragm joint,and has been widely studied.The typical internal-diaphragm joint has problems such as convex beam and column,additional cover plates which are not conducive to the construction of self-supporting floor slabs,etc.The large number of cold-formed rectangular tubes applied also brings challenges for the internal-diaphragm connection in recent years.Therefore,a new joint is proposed in this study for the connection of the I-beam and wide concrete-filled rectangular steel tubular(CFRST)column.Two split endplates are welded to column at the upper and lower flange,with sideplates on both sides of the CFRST column to meet the bending requirements;and holes are drilled in the flanges according to a certain way of regularity to reduced the steel beam to avoid the cover plate design while making the joint plastic hinge occur in the reduced area.This joint ensures its seismic performance while removing the internal-diaphragm and cover plate settings,can be used for practical production.In this thesis,the seismic performance of the proposed new joint is investigated through experimental study,numerical analysis and theoretical derivation to establish a complete framework for research.(1)Experimental study.A total of 10 specimens with different reduced types were designed for tests,then the test data and phenomena of each specimen were obtained.The failure modes of the joint were evaluated based on the analysis of test phenomena.The evaluation indexes such as hysteresis curve,skeleton curve,secant stiffness,ductility coefficient and equivalent viscous damping coefficient of the specimens were used to evaluate the strength,energy dissipation capacity,ductility,stiffness and other seismic performance of the relevant specimens.Additionally,the specimens were classified in terms of stiffness and strength based on the moment-rotation angle curve according to EC3.(2)Numerical analysis.Based on the combined plastic with ductile damage model of steel and the concrete damaged plasticity(CDP)model,suitable contact conditions and boundary loading,the finite element model is established using the finite element software ABAQUS,the validity of the finite element model is verified by comparing the hysteresis curve,elastic stiffness,failure mode and stress distribution obtained by FE model with the experimental results.Equivalent plastic strain(PEEQ)is adopted as the fracture performance evaluation parameter,and critical paths are established for the weak locations of specimen damage.ABAQUS model J4(drilled circle holes)as the base specimen,by varying end-plate thickness,beam length,Initially reduced distance,drilled-holes types,the hysteresis performance and failure modes are analyzed separately.The distribution of PEEQ values of the paths under each parameter series,stress distribution,elastic stiffness of moment-rotation angle curve,peak bending moment and failure angle,energy dissipation capacity and other evaluation indexes are compared in the performance comparison.(3)Theoretical derivation.Based on the previous experimental research and numerical analysis,the initial stiffness of the joint is specially studied.Based on the design methods of the component method,the initial rotational stiffness of the reduced joint in this paper is obtained by using a suitable simplified spring model and an elastic plate system to calculate the formula.The theoretical calculation results is compared with the finite element results for a range of commonly used geometric parameters,and which has good predictability. |
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