Cyclic performance of dual stage energy dissipation joints for connecting CFST column and exterior wide-flat beam

Based on the design concept of high energy dissipation and replaceability, as well as the specific characteristics of underground structures, such as difficulties and uncertainties in excavation, a dual stage energy dissipation joint for connection concrete-filled steel tube (CFST) column-exterior wide-flat beam joint was proposed in this paper. Three types of joints were designed and manufactured. Specifically, typical CFST column-exterior wide-flat beam joint (abbreviated as typical joint, TJ), frictional energy dissipation CFST column-exterior wide-flat beam joint (abbreviated as frictional energy dissipation joint, FEDJ), and dual stage energy dissipation CFST column-exterior wide-flat beam joint (abbreviated as dual stage energy dissipation joint, DEDJ). Then, quasi-static seismic performance tests and finite element analyses were conducted to these three joints. After that, the technique for order of preference by similarity to ideal solution (TOPSIS) method was used to assess the seismic performance of different types of joints. The results indicated that the DEDJ exhibited frictional and rotational energy dissipation characteristics under service level earthquakes, while demonstrating plastic deformation energy dissipation through metal components during design basis and maximal considered earthquakes. TJ showed bending failure at beam ends, whereas failure in DEDJ was concentrated in steel energy dissipation components. FDEJ remained undamaged throughout the test. TJ demonstrated high bearing capacity but suffered from poor ductility, rapid strength/stiffness degradation, and limited energy dissipation capacity. FDEJ maintained stable strength/stiffness with good ductility, though constrained by low bearing capacity and insufficient energy dissipation capability. DEDJ not only achieved the designed bearing capacity target but also synergistically combined advantages from both TJ and FDEJ, exhibiting superior ductility, effective energy dissipation, and slower strength and stiffness degradation compared to TJ. The assessment result of the TOPSIS method showed that the comprehensive performance of the DEDJ was better than that of TJ and FEDJ. the bearing capacity and energy dissipation capability of DEDJ may be compromised when the axial compression ratio increased to 0.5 and the end-to-center ratio of low-yield-point steel reached 1.82.