The Earthquake Engineering Online Archive

Rational design methods for light equipment in structures subjected to ground motion

Sackman, Jerome L.; Kelly, James M.

UCB/EERC-78/19, Earthquake Engineering Research Center, University of California, Berkeley, 1978-09-01, 72 pages (645/S22/1978)

An analytical method is developed whereby a simple estimate can be obtained of the maximum dynamic response of light equipment attached to a structure subjected to ground motion. The natural frequency of the equipment, modeled as a single-degree-of-freedom system, is considered to be close, or equal, to one of the natural frequencies of the N-degree-of-freedom structure. This estimate provides a convenient, rational basis for the structural design of the equipment and its installation. The approach is based on the transient analysis of lightly damped tuned or slightly detuned equipment-structure systems in which the mass of the equipment is much smaller than that of the structure. It is assumed that the information available to the designer is a design spectrum for the ground motion, the fixed-base modal properties of the structure, and the fixed-base properties of the equipment. The method can also be used to treat estimates of the maximum acceleration and displacement of the equipment. The method can also be used to treat closely spaced modes in structural systems, where the square root of the sum of squares procedure is known to be invalid. This analytical method has also been applied to untuned equipment-structure systems, for which the conventional floor spectrum method is mathematically valid. A closed-form solution is obtained which permits an estimate of the maximum equipment response to be obtained without the necessity of computing time histories, as is required by the conventional floor spectrum method.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-78-19.pdf (4 MB)