Q. Seismic Loads For Structure-Mounted Equipment?

For equipment mounted in a structure above grade, the governing equation for seismic force is:

F_p = A_vC_cPa_cW_c, where A_v = (a site-specific value, equipment seismic coefficient C_c=5), and performance criteria factor P=1.0.a_c=1.0, except for flexible equipment such as tall slender vessels, vessels on tall legs springs, or other resilient supports.  This factor is then given as follows: for T_c/T<0.6 or T_c/T>1.4, a_c=1.0; for T_c/T³0.6 or T_c/T£1.4, a_c=5.0. 

T_c is the first natural period of the equipment, and T is the first natural period of the structure.  W_c is the operating weight of the equipment.  F_p is the horizontal seismic force, applied at the center of gravity of the equipment and in the direction causing the highest stresses. The design of pressure retaining elements (both internal and external) shall permit allowable stress multiplying factors.