Development and use of seismic instructure response spectra in nuclear plants

This paper encompasses methods for the development of instructure response spectra as well as the use of these spectra in the seismic design and analysis of nuclear plant components. The time history modal analysis method to generate instructure response spectra is described. This includes the effects of rigid body transformation associated with angular accelerations of the lumped mass nodal points due to eccentric locations of the equipment or system support points. A general method of generating and using the instructure response spectra associated with both translational and angular input motions is presented. An approximate way of treating light equipment mounted on relatively flexible floors or shear walls is considered.Various numerical techniques for the integration of differential equations of motion are outlined. The time interval to be used is chosen so as to avoid mathematical instability and inaccuracy. Comparison of the results using different techniques for the numerical integration of a sample problem, for the purpose of verifying solution accuracy, is provided. Consideration is given to determining how small the period interval should be in generating instructure response spectra to avoid truncation of resonance peaks. The use of three-dimensional instructure response spectra developed for each of the three orthogonal translational directions of ground motion is presented. Methods of developing instructure response spectra other than the time history method are discussed.