Q. Seismic Loads For Structure-Mounted Equipment?
For equipment mounted in a structure above grade, the governing equation for seismic force is:
Fp = AvCcPacWc, where Av = (a site-specific value, equipment seismic coefficient Cc=5), and performance criteria factor P=1.0.ac=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 Tc/T<0.6 or Tc/T>1.4, ac=1.0; for Tc/T³0.6 or Tc/T£1.4, ac=5.0.
Tc is the first natural period of the equipment, and T is the first natural period of the structure. Wc is the operating weight of the equipment. Fp 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.