Constructing mathematical models of cable tray and support systems to determine seismic response in nuclear plants

The problem is to construct a stick model with lumped masses representing the cable tray/support system in a nuclear plant subjected to seismic forces. The equivalent physical and geometric properties of the lattice sub-system to be changed into the theoretical stick components must be determined. The effective moment of inertia and shear area of the lattice structure are best ascertained by static load tests; damping ratios, by dynamic tests. Properties of non-lattice components are known from given data or can be readily calculated. Engineering judgement is required to fix the size and location of lumped masses. A study of a steel ladder type cable tray in the transverse direction considered as a plane frame serves to show how a lattice sub-system is changed to a mathematically equivalent stick component. (Auth.)