Effects of Connecting Damper on Rocking Motion of Multiple Cabinets Subjected to Seismic Excitation

Abstract

In various industrial plants such as thermal power plants, nuclear power plants and chemical plants, numerous cabinets are used for storing the electronic circuits and devices used for controlling the plants. These cabinets are very important for maintaining stable plant operation. Some of these cabinets are simply placed on the floor as free-standing structures, and in many cases, they cannot be connected to the floor using bolts or other means for various reasons. Thus, if these cabinets are subjected to very strong seismic excitations, they will experience very large rocking motions. In the worst case, they will overturn, and the installed electronic circuits or devices will collapse which will cause a loss of plant control and could result in significant accidents. Thus, rocking motion suppression methods have been proposed for these free-standing structures. The authors have also been investigating a method that utilizes a gyro system. Connecting adjacent buildings by damping devices is a well-known architectural mitigation method that is very effective at mitigating their seismic response. The effectiveness of this method was confirmed during the Great East Japan Earthquake in 2011. In this paper, we apply the above-mentioned connecting method to free-standing cabinets in order to suppress rocking motion. There are various types of connecting devices, such as a viscous damper. In this paper, considering the characteristics of these dampers, an elasto-plastic damper is adopted as a connecting device. Analytical models of the rocking motions of control cabinets are established, and the connecting devices are expressed as dampers with a bilinear-type force-displacement characteristic. The rocking motions of the cabinets are analyzed for sinusoidal and seismic excitations by changing the aspect ratio of the cabinets, along with the yield force in the bilinear hysteretic curve. The effects of connecting devices and various parameters are evaluated and discussed in comparison with the rocking motion of a single cabinet. It is found that the proposed connecting method is very effective in suppressing the rocking motion of the free-standing cabinets subjected to base excitations when the hysteretic characteristics are properly adjusted.