Seismic properties, calculation method, and equivalent model of internal connection in modular steel building

Modular steel building (MSB) is a new type of building structure in which prefabricated modules are transported to the construction site and assembled through connections, indicating that the connection between module units has a great influence on the properties of MSB. Since the internal connections of MSB require installation operation space, reliable seismic properties, and cannot conflict with other components within the modular unit, the requirements for internal connection are higher than those for external connections. In this paper, two forms of internal connections, two-direction connection form (2-DCF) and three-direction connection form (3-DCF), were proposed, and the seismic properties of the two connections were investigated. Due to its three-directional spatial connections, the 3-DCF exhibits a stronger semi-rigid connection and a full-strength connection compared to the 2-DCF. To further optimize the design parameters, a parametric study was conducted on the seismic properties of 3-DCF, in which the bolt preload and the thickness of box connector (BC) has a significant effect on the stiffness of 3-DCF. In addition, the calculation method of skeleton curve of 3-DCF was proposed and evaluated, and the equivalent model of 3-DCF was established and verified to accurately reflect its cyclic properties. Finally, the equivalent model of 3-DCF was applied to a four-story three-span MSB for calculation and it was found that 3-DCF can effectively reduce the dynamic response of MSB compared with the prescribed hinged connection, which can provide a reference for the design and use of the internal connections in MSB.