Flexural performance of a novel bolted inter-module connection affected by corner fitting openings

Modular Steel Buildings (MSBs) are innovative structures composed of prefabricated components. The inter-module connections (IMCs) are crucial for convenient on-site assembly and overall structural integrity. Numerous IMCs exhibit openings in corner fittings to provide construction space, which reduces the strength and stiffness. The effect of these openings on flexural performance, however, remains unquantified. This study, therefore, examines the impact of opening size on the flexural performance of corner fittings, using a novel bolted IMC as an example. Flexural performance was assessed using horizontal monotonic loading tests on three specimens, with variables including box length and opening size. The failure modes, load-displacement curves, rotational stiffness, and strain responses were obtained. Subsequently, a detailed finite element (FE) model, validated against experimental data, enabled a parametric analysis on bolt sizes, end plate thickness, and opening width. Parametric analysis indicates that increasing the end plate thickness from 14 mm to 20 mm raises ultimate load-bearing capacity by 85.51 % and stiffness by 82.95 %. Theoretical formulas based on yield line theory and the component method were derived to evaluate yield load-bearing capacity and initial rotational stiffness of IMCs, considering the effect of opening size. Comparsion of these formulas with experimental and FE model resuts demonstrated good accuracy, with deviations of 9.96% for initial rotational stiffness and 12.13 % for yield load capacity, respectively. Finally, the working mechanism by which openings influence the flexural performance of IMCs is further discussed and clarified.