Development and seismic performance assessment of welded connections in modular steel structures for high-rise buildings

Modular steel structures are characterized by rapid construction, high quality, reduced labor requirements, and flexible layouts. Ensuring the seismic performance of inter-module connections is critical for structural safety. This study investigates the seismic behavior of novel modular steel frame joints (MSFJs) through low-cycle reciprocating load tests on three full-scale specimens. The effects of outer sleeve height and thickness on key seismic performance indicators-including failure modes, stress response, ductility, energy dissipation, and stiffness-are systematically evaluated. Experimental results revealed that MSFJs primarily exhibited bending failure at beam ends, with most failures occurring at welds between beam flanges and column ends. The hysteresis curves were full, with peak equivalent viscous damping coefficients (he) reaching 0.15, indicating strong energy dissipation. MSFJs underwent four stress stages: initial slipping, elastic deformation, elastic-plastic deformation, and failure. The height and thickness of the outer sleeve had minimal impact on peak loadbearing capacity and ductile deformation. The residual deformation curve showed a two-stage trend with stable performance degradation and a strength degradation coefficient (lambda i) between 0.90 and 1.00. Overall, MSFJs demonstrated semi-rigid, partial-strength joint behavior, providing valuable insights for the seismic design and optimization of modular steel structures.