The seismic response of rack warehouses is known to be reduced by horizontal sliding of the warehouse contents, which act as mass dampers. However, in past earthquakes business continuity has been interrupted due to damage from spilling, toppling or falling contents. In this paper, response control using seismic isolation is investigated. Because the total rack weight is constantly changing and the rack is often loaded at large eccentricities, Spherical Sliding Bearings (SSB) are proposed, which exhibit natural periods independent of the supported weight. Based on numerical and experimental test results undertaken previously, an analytical model is proposed including pressure and velocity dependent friction values. Using the proposed model, the performance of a seismically isolated rack warehouse with variable weight and eccentricity is studied and compared with conventional rubber bearings.
Although rubber bearings are popular in Japan as seismic isolation bearings, spherical sliding bearings (SSBs) or friction pendulum bearings are widely used in many countries, including the U.S. In this study, shake table tests on a braced frame supported by SSBs are carried out, and their dependence on pressure and velocity is investigated. Tests under eccentric dead loads and uplift conditions are also conducted to capture their performance. Analytical models that consider pressure and velocity dependence are proposed, and their validity against the experimental results is discussed.
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