Response Spectrum Method in Seismic Analysis and Design of Structures

In recent years, new developments have taken place leading to the calculation of seismic stresses which are more accurate as compared to those obtained by the conventional methods. In most cases, these accurate seismic stresses are also significantly lower than those obtained from conventional methods. These developments are rigorous, yet lead to elegant mathematical formulation. As a rule, the increase in computational cost is minimal. Application of these methods will be useful in the seismic design of critical structures and equipment. For facilities already designed and constructed, these more accurate methods can be used in situations where the facility has to be reassessed for higher loads, and also in the calculation of margins. Reduction in seismic stresses can be used in the reduction of snubbers and other piping supports. In new construction, the reduced seismic stresses will result in more efficient and economical design. Background theoretical information is presented in simplified form. New methods of combining responses from various modes and from three components of earthquake are included.
Some of these methods are accepted in the new ASCE standard on the seismic analysis of nuclear power plants and lead to significantly lower estimation of combined stresses. New methods of evaluating seismic response in secondary systems (equipment, piping) are discussed.