Seismic structural analysis of a glovebox by the equivalent static method

Seismic strength evaluation of equipment requires efficient and accurate methods. Such an evaluation generally calls for dynamic analysis requiring detailed accelerations and advanced mathematical modeling. The analysis may be tedious, but in theory works for any structure with any boundary conditions. Many equipment do not justify such expansive and expensive evaluation; hence, efficient and inexpensive, but may be more conservative, methods of analysis are used instead. The equivalent static method (ESM) is such a method. Being a static method, the ESM can not be directly applied to equipment that are not simply anchored to or only rest on the ground. In this paper, the authors show how a glovebox with ambiguous anchorage conditions is analyzed by the ESM when subjected to the seismic load. Also outlined are the retrofits to increase its seismic resistance. The recommendations include fixing the legs to the floor and using inclined braces. The use of braces is effective in resisting the lateral seismic load. It redistributes the seismic-generated moment and force in a more benign way. It also significantly stiffens the glovebox's supporting table structure, thus raising the vibrational frequency of the table away from the high-energy range of the seismic load and drastically reduces the displacement of the glovebox