Seismic performance and design of an innovative dual vertical diaphragms joint between flat CFST column and H-beam

Steel-concrete composite structure is one of the research hotspots in the structural engineering field in recent years. Among the various types of composite structures, flat concrete-filled steel tube (CFST) column structures are preferred for residential buildings owing to the smooth elevation to coordinate with the indoor decoration. The seismic performance of beam-to-column joints is momentous as a key part of flat CFST column structures. This study provided a new type of joint between flat CFST column and H-beam with dual vertical diaphragms through the column. The design procedure for the vertical diaphragms was proposed to design the test specimens. An experimental study on the seismic behavior of the innovative joint under cyclic load was performed on three full-scale specimens. The seismic performance of the joint, including the failure mode, hysteretic and skeleton curves, ductility and energy dissipation capacity, was observed and discussed in detail. Subsequently, nonlinear finite element models (FEMs), based on the specimens, were developed using the ABAQUS/Standard program and validated by comparing the numerical results with the test ones. The experimental and numerical results demonstrated that the proposed joint exhibited satisfactory seismic performance and all the specimens exhibited a ductile failure mode. The failure process and damage distribution of the joint under earthquake were revealed based on the validated FEM. Furthermore, a mechanical model was established to predict the load-bearing capacity of the shear force and bending moment of the proposed joint. The mechanical model was validated to be accurate and reliable by comparing the numerical simulation results with the theoretical ones. This study provided a practical joint between flat CFST column and H-beam as well as its design method, which was beneficial for the promotion of the flat CFST column structures.