In various industrial plants such as thermal power plants, nuclear power plants, and chemical plants, many cable trays are generally used to support cables for control signals. Cable trays are very long, and thus are supported from ceilings or walls by many supporting structures. When the cable trays are subjected to strong seismic excitations, the trays or the supporting structures vibrate with large amplitudes. In the worst cases, they can collapse, and plants can lose control of systems, which can lead to severe accidents. Therefore, it is very important to maintain the structural integrity of cable trays during seismic events including recent severe earthquakes such as the East Japan Earthquake in 2011.
Cable trays are generally made of thin steel plates with sides folded in the vertical direction, and with cables simply placed on the tray. Thus, cables can slide when the inertia force on the cables exceeds the friction force between the tray and cables. The mass of the cables is relatively large compared to that of a tray, thus the natural frequency of the tray will change significantly due to the cable sliding motion. Consequently, seismic responses of cable tray will also depend on the sliding motion of cables. Therefore, cable trays are seen as highly nonlinear structural systems.
In this study, seismic responses of cable trays are investigated analytically considering cable sliding motions. A cable tray is modeled by a two-degree-of-freedom system. Response acceleration, and the displacements of the tray and the cable are evaluated for both sinusoidal and seismic inputs by varying the cable mass or friction coefficient between the tray and cables. It is confirmed that the sliding motion of the cable has a very large influences on the seismic responses of the cable-tray system.