Sliding Fragility of Unrestrained Equipment in Critical Facilities
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Earthquake vulnerability of nonstructural components is usually reduced by fastening or bracing individual objects. However, there are some nonstructural components in buildings which often cannot be retrained for protection from earthquake shaking. The response of these objects will consist sliding, rocking, or jumping. Understanding these response types will allow estimation of vulnerability to earthquake damage and will assist in the design of appropriate mitigation measures. This research concentrates on experimental and analytical studies of the sliding response of freestanding rigid objects subjected to base excitation. Analytical and experimental techniques are combined to allow determination of fragility curves for free-standing rigid equipment under seismic excitations for further improvement of seismic mitigation measures. A discrete system model, an analytical model for two-dimensional sliding under two-dimensional excitation, is developed and analyzed for specific base motions. Shaking table testing with a range of excitation, is developed and analyzed for specific base motions. Shaking table testing with a range of excitations and system parameters is used to define stability bounds for pure sliding motion. A comparison of the analytical and experimental results is then performed to further verify the validity of the analytical model. Discrepancies in the model assumptions and future improvements of the nonstructural model are also discussed in this report. The appendices present 1) the numerical method for sliding problems; 2) the SIMQKE program; and 3) a table for static and dynamic friction coefficients.