Corner-supported modular structures are made of repetitive prefurnished, prefinished modular units, which are fabricated in a factory and transported to the site of a building to form a permanent building block. The modular units are then tied together through the use of so-called inter-modular connections, or inter-connections, which form a different configuration at joints compared to conventional steel structures. The presence of inter-connections in these structures, in addition to beam-to-column connections or intra-connections, may change their dynamic characteristics, including natural frequencies, mode shapes, and damping ratios. This paper aims to investigate the dynamic characteristics of a modular building through the use of operational modal analysis (OMA). A half-scaled three-storey modular structure, designed and instrumented with highly sensitive accelerometers, was experimentally tested under pure and randomly generated vibrations. The time history of the response acceleration of the structure was recorded using a data acquisition system. Different output-only techniques of OMA, based on both frequency and time domains, were employed to analyse the recorded response acceleration of the structure and extract the natural frequencies, mode shapes, and damping ratios. These techniques are peak picking (PP), enhanced frequency-domain decomposition (EFDD), and stochastic subspace identification (SSI). The outcomes in this paper can be used for further research on the development of an experimental formula for the design of multistorey modular buildings against lateral loads.

The use of friction pendulum system (FPS) as a base isolation system is one of the efficient and reliable techniques for seismic response reduction of liquid storage tanks. However, recent studies have shown that the FPS may experience substantial displacements under pulse-like near-fault earthquakes, which could lead to the collision of its articulated slider against the retainer ring. This internal impact in the FPS can make the isolation system less effective or even damaged. The best solution to this problem is to provide an appropriate displacement capacity of the FPS bearing to accommodate the resulting movements. However, due to any practical limitation or under extreme ground motions, the base displacement may exceed the displacement capacity provided and an internal impact may occur. This paper proposes and investigates the use of elastic and viscous bumpers in FPS-isolated tanks subjected to near-fault earthquakes to limit excessive bearing displacements and to prevent direct impact with the retainer. The material properties of the bumpers and their initial gap distance are used as variable parameters in the nonlinear time-history analyses of selected isolated tanks with different aspect ratios. The results, while showing the advantages of viscous bumpers over elastic ones, indicate the effectiveness of both shock absorbers in isolated tanks that are subject to large displacement demands. Based on the results of the parametric study, design recommendations are given for the use of such bumpers in FPS-isolated tanks.