Generation of floor response spectra for PFBR RCB

This paper describes the generation of floor time histories and corresponding floor response spectrums at various locations in reactor containment building (RCB) for 500 MWe Prototype Fast Breeder Reactor (PFBR). The RCB and its internal structures are modeled with equivalent 3D-beam elements (stick model), which have got the essential global stiffness and inertial properties of the corresponding building. The main aspect in the simulation of beam model is derivation of equivalent cross sectional properties such as bending, torsional and shear rigidities including shear centers. These properties have been obtained through 3D plate/shell element models with appropriate kinematic constraints, for the zones between floors of corresponding buildings. The stick model includes a set of springs and dampers to simulate soil effects, on which base raft and various sticks are mounted. The soil stiffness and damping values are derived based on equations given in ASCE-98. Time history analysis has been done using three uncorrelated time histories, which are derived from the site dependent design response spectra. Floor time histories (FTH) are extracted at important locations from which the corresponding floor response spectrums (FRS) have been generated for various damping values. Peak broadening of the response spectrums has been done according ASCE criteria. Floor response spectrum corresponds to reactor assembly support shows amplification 2.5 for SSE and 3 for OBE. CASTEM 3M is used for seismic analysis and generation of FRS. (author)