Experimental and numerical investigation on the seismic behavior of a novel bolted inter-module connection

Modular steel buildings (MSBs) are innovative structures comprising complete components. The design of inter-module connections (IMCs) significantly influences onsite assembly convenience and overall structural performance. IMC designs often incorporate openings in corner fittings' side plates for installation ease, though these may compromise structural integrity. Existing research reveals three main gaps: limited focus on IMC performance under combined loading, inadequate study of openings' impact on seismic resilience, and absence of a restoring force model for unit connections. This study introduces a novel bolted IMC design featuring variable opening sizes. Seismic performance under combined loading was evaluated via experiments and finite element analysis (FEA), leading to a developed restoring force model. Four specimens underwent horizontal quasi-static loading tests under axial pressure, revealing failure modes, hysteresis curves, stiffness degradation, and energy dissipation. A detailed FE model was validated with experimental data, and parametric analysis varied axial compression ratio, bolt sizes, and end plate thickness. Results indicate the new bolted IMCs exhibit satisfactory seismic performance. However, openings significantly reduce seismic resistance, with increased box length notably enhancing it. A restoring force model (RFM) derived from skeleton curves, stiffness degradation, and hysteresis rules correlates well with experimental hysteresis curves, effectively capturing IMCs' seismic response. This model serves as a foundation for designing modular structural systems.