Theoretical and Experimental Evaluations on Cooperative Bending Behavior of Laminated Channel Beams in Modular Steel Buildings

Modular steel buildings that employed off-site prefabricated volumetric units offered advantages in construction speed and sustainability. The highly integrated buildings assembled by only column-to-column connections were prone to a global collapse, and beam-to-beam connections could greatly promote the overall mechanical performance. However, cooperative bending performance has not been fully understood from a theoretical perspective, and therefore, a performance-based structural design cannot be conducted in practical engineering. In the present study, the laminated double beams in modular steel buildings were theoretically and experimentally investigated. Theoretical models for interfacial slip strain and slippage were established based on differential equations, accounting for both frictional and bolted connection types. In addition, mathematical expressions for bending curvature incorporating interfacial slip were derived, leading to a theoretical procedure for calculating the equivalent initial bending stiffness. In this way, the mechanical performance of laminated beams was analyzed, and the superimposed bending effect was further evaluated. The results demonstrated that bolted connections improved bending capacity by approximately 8% and increased initial bending stiffness by 17–28% compared to friction-only connections. The proposed stiffness prediction models showed significant agreement with experimental data, providing a theoretical basis for the structural design of laminated beams in modular steel buildings.