Development of a Hybrid Rubber Damper–Restrainer System for Modular Steel Structures

Inter-module connections govern force transfer, relative displacement and energy dissipation in modular steel structures subjected to seismic-type loading. This study aims to develop and experimentally characterise a full-scale Hybrid Rubber Damper–Restrainer Connection (HRDRC) for modular steel inter-module joints, investigate the effects of combined High-Damping Rubber Bearing (HDRB)–Hyper-Elastic Rubber Restrainer (HERR) action and vertical loading on connection-level cyclic response, and validate the observed behaviour using calibrated nonlinear link elements in ETABS 2023. The principal contribution is the connection-level implementation and experimental characterisation of the combined HDRB–HERR mechanism within a single replaceable inter-module assembly. A full-scale prototype was tested under displacement-controlled cyclic loading using a servo-controlled dynamic actuator. Six configurations were investigated under unloaded, compressive and tensile vertical-loading conditions, and their hysteretic response, peak lateral resistance, effective stiffness, effective damping coefficient, energy dissipation capacity and equivalent viscous damping ratio were evaluated. The HDRB-only configurations exhibited stable and nearly symmetric hysteresis, whereas the HERR provided substantial restraining resistance and large-deformation capacity. The hybrid configurations developed fuller hysteresis loops and increased force mobilisation through the combined damping–restraining mechanism. Under 3 kN compression, the DRVC configuration reached a peak lateral resistance of 53.51 kN at 30 mm displacement amplitude. The HERR pull-over test sustained approximately 42 kN at about 125 mm displacement before rupture. The calibrated nonlinear-link model reproduced the principal connection-level response with an overall mean error of 5.83%. Building-level effects, including inter-storey drift, residual displacement and post-earthquake functionality, were not quantified.