Study On The Seismic Performance Of Concrete-filled Double Skin Steel Tubular Column Base With Bolted End-plate

The concrete-filled double skin steel tubular(CFDST)structure possesses the characteristics of light weight and good seismic performance owing to the coolaberative working mechanism of steel tubes and sandwiched concrete.It has been used in transmission poles and towers,while the columns and foundations are usually connected by bolted end-plates bases.It is important to clarify the interaction between various components in the column base area for the further application of such structure.In this thesis,the seismic performance of CFDST column base with bolted end-plates is studied both experimentally and theoretically.The main work is summarized as follows:(1)The static behavior of CFDST joint with bolted end-plates is studied.The experimental research and finite element analysis are carried out for the column-tocolumn connections under axial tension and pure bending conditions.The results show that when compared to the hollow section counterparts,the prying force of end-plates decreases due to the support effect of sandwich concrete and inner steel tube.The calculation methods of the axial tensile capacity and pure bending capacity of the flanged joints are proposed based on the parametric analysis.(2)Experimental study on the seismic performance of CFDST bolted end-plates base is carried out.The specimens are designed with unstiffened flange,and the main parameter is the axial compression ratio.The effects of initial stress and long-term loading are considered,and the long-term performance tests of corresponding concrete materials are also conducted.The load-displacement relationship,strain distribution,strength and stiffness degradation of the specimens are obtained and analysed.The test results show that the specimens have compression bending failure at the column bottom sections,and the ductility and energy dissipation capacity are favorable.(3)The finite element(FE)analysis on the seismic performance of CFDST bolted end-plates base is conducted.An advanced FE model is established to simulate the loaddisplacement relationship and loading-unloading characteristics of bolted end-plates column bases under cyclic loading,taking into consideration of the time-dependent effect of materials,the constraint of steel tubes on concrete,the steel fracture,the concrete damage,and the component contact.Based on the validated numerical model,the failure mode of bolted end-plates base is analyzed,the influence of initial stress and long-term loading on the seismic performance of the base is revealed.The failure mechanism,the load transfer mechanism and the internal force distribution of column base are clarified.(4)The design method of CFDST bolted end-plates base is proposed.The influence of key parameters on the seismic performance of base is revealed,such as the flange dimension,the diameter and number of bolts,the cross-sectional norminal steel ratio,the long-term sustained loading time and the constructional load ratio.Based on the parametric analysis,the simplified design method for the bearing capacites,the hysteretic model for the column base and the construction suggestions are proposed.The results show that the predicted capacities using proposed methods are in good agreement with experimental and numerical ones.