The Influence of Semi-Rigid Connection Stiffness on the Seismic Response of a Four-Story Steel Modular Box Building Influence of Semi-Rigid Connection Stiffness on the Seismic Response of a Four-Story Steel Modular Box Building

Abstract

Steel modular buildings rely on inter-module connections to transfer lateral forces and maintain global stability. However, treating these connections as fully rigid may overestimate structural stiffness and underestimate story drift. This study evaluates the effect of measured connection flexibility on the seismic response of a four-story modular box building. A three-dimensional global model was developed in ETABS, while the rotational stiffness of the existing bolted bracket connection was obtained from a detailed finite-element model and represented as panel-zone rotational springs. The secant rotational stiffness was 2,190.16 kN·m/rad for a continuous-column joint and 1,095.08 kN·m/rad for top and bottom joints. The stiffness classification indicated that the existing connection behaved as a simple-to-partially restrained connection rather than a fully restrained moment connection. When the connection stiffness was included in the global model, the maximum column demand-to-capacity ratio reached 1.048 and the amplified interstory drift ratio reached 0.0269, exceeding the adopted limits of 1.00 and 0.02, respectively. The results demonstrate that realistic connection stiffness should be incorporated in the global analysis of modular steel buildings and that strengthening is required before the connection can be relied upon as part of the seismic-force-resisting system.