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Dynamic response of light equipment in structures
Der Kiureghian, Armen; Sackman, Jerome L.; Nour-Omid, Bahram
UCB/EERC-81/05, Earthquake Engineering Research Center, University of California, Berkeley, 1981-04, 60 pages (635/D43/1981)
Perturbation methods are employed to determine the dynamic properties of a combined system composed of a multidegree-of-freedom structure to which a light, single degree-of-freedom equipment item is attached. Closed-form expressions are derived for the natural frequencies, mode shapes, modal dampings, and other modal properties of the combined system in terms of the dynamic properties of the structure alone and the equipment alone. The derived properties are used to determine the response of the equipment when the structure is subjected to a random input excitation. For earthquake-type excitations, a response spectrum method is developed whereby various statistical measurements of the equipment response are given directly in terms of the input ground response spectrum. Tuning and equipment-structure interaction are included. The method efficiently generates floor spectra which include the effect of interaction. The conventional floor spectra, which disregard interaction, are obtained simply by setting the equipment mass equal to zero. For an example structure, the results based on the developed method demonstrate remarkable agreement with a numerical analysis employing a set of 20 simulated ground motions.
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