ABSTRACT
We have pointed out in Chapter 6 that for various practical reasons it is customary to perform the analyses of the primary system (building) and the secondary system (HVAC, piping, equipment, etc.) separately, or to assume that the two systems are uncoupled. It is shown there that the uncoupled analysis of the secondary system introduces considerable error in the seismic response on the conservative side. A method of performing the analysis of the coupled system is presented in Chapter 6, which is based upon using an approximate technique to evaluate the coupled mode shapes and frequencies. In fact the same method can be employed to give the coupled response of both the primary and secondary systems. There is another practical problem, however. In chronological order, the design of primary system precedes the design of the secondary system. At the time the primary system is being designed, only tentative information, if any, about the secondary system is available. Therefore, the uncoupled analysis of primary system is a fact which cannot easily be altered. There is a need to have approximate criteria which can be used to evaluate the effect of decoupling on the primary system response.
