Sliding friction-based lateral-gravity decoupling system for concrete modular building

Balancing seismic performance with degree of prefabrication remains a primary challenge in concrete modular buildings. Existing connection methods have difficulty achieving both high prefabrication efficiency and reliable seismic performance. Conventional connections either increase on-site wet construction (e.g., grouted sleeves) or compromise seismic performance (e.g., bolted connections). To improve both prefabrication efficiency and seismic performance, this paper proposes a novel sliding friction-based lateral-gravity decoupling system (SF-LGDS), which separates the gravity force-resisting from the lateral force-resisting: a concrete modular building with flat sliding connections (FSCs). Gravity loads are transferred through the modular frame, while lateral seismic resistance is mainly provided by the shear walls. The FSCs allow controlled horizontal sliding between upper and lower modules at a low force threshold, achieving low-damage characteristics. Meanwhile, the use of bolted assembly in the FSCs improves the degree of prefabrication and reduces on-site wet construction. To validate the behavior of the FSCs, full-scale tests were conducted. The results demonstrate that the FSC exhibits stable, rigid-plastic Coulomb friction behavior, with consistent hysteretic response and no noticeable strength or stiffness degradation. Numerical simulations were further conducted in OpenSees to evaluate the seismic performance of the SF-LGDS. The results indicate that the shear walls provide effective lateral restraint and ensure coordinated deformation among the modules. Compared with the building using the modular in-fill method, the SF-LGDS shows significantly less damage in the modular frame, at the expense of relatively larger inter-story drift. Under major earthquakes, the modular frame in the SF-LGDS remains almost elastic, with slight damage. The main damage is concentrated in the shear walls, which act as the primary lateral force-resisting system. These results indicate that the SF-LGDS can improve prefabrication efficiency and protect the modular frame under earthquakes.