Seismic performance of CFDST composite frames with different joint types under unidirectional and multi-directional earthquake excitation

Concrete-filled double-skin steel tube (CFDST) structures exhibit excellent seismic potential. However, existing studies have primarily focused on the component or joint level, with limited research addressing the overall structural performance under unidirectional and multi-directional earthquake excitation. The four frame models were developed by combining three types of joint configurations (ring plate, vertical stiffener plate, and extended endplate) with two types of column cross-sections, CFDST and concrete-filled steel tube (CFST). Finite element modeling and nonlinear dynamic time-history analysis were performed to evaluate the seismic performance of the four frame models in terms of ultimate seismic capacity, roof displacement response, inter-story drift angle, axial load ratio response, local stress-strain response, plastic zone distribution, and plastic energy dissipation capacity. The results indicated that the ring plate and vertical stiffener plate models exhibited higher stiffness and strength, contributing to improved structural stability under moderate to severe earthquake excitations. Compared with CFST columns, CFDST columns were more effective in restraining the development of plastic zones at the column ends, thereby enhancing the seismic capacity and ductility reserve of the frames. Among the four models, the ring plate CFDST frame demonstrated the smallest lateral displacement response and the greatest plastic energy dissipation capacity, while the extended endplate frame exhibited the largest lateral displacement and the weakest energy dissipation performance. The results provide a basis for upcoming shake table studies and practical structural design.