Response Spectra for Seismic Analysis and Design
Earthquakes are one of the greatest natural disasters to human life and properties. Following lessons from previous earthquake disasters, the performance-based seismic design is increasingly accepted by engineers to prevent seismic disasters. In performance-based seismic design, realistic and reliable design response spectra are required to reliably and accurately predict responses of designing structures. However, the mostly used ground response spectra, i.e., Newmark design spectrum and Uniform Hazard Spectrum on soil surface, and floor response spectrum constructed by current methods do not properly meet the requirements of performance-based seismic design: 1. Newmark design spectrum exhibits lower amplitudes at high frequencies and higher amplitudes at low frequencies. Thus, it cannot realistically and reliably reflect seismic features of target sites. 2. Variability of soil parameters, nonlinear property of soils, and vector-valued seismic site response analysis are not integrated into the process of constructing Uniform Hazard Spectrum on soil surface in modern methodologies. Thus, the desired design response spectrum is not realistically and reliably represented. 3. An efficient method to generate probabilistic floor response spectrum considering random ground motions has not been addressed. The direct spectra-to-spectra method to generate floor response spectrum is superior to the time history analysis method in efficiency. However, this method is not applicable currently to generate probabilistic floor response spectrum. The objective of this study is bridge the gap between performance-based seismic design and realistic design response spectra. 1. Considering the problem of Newmark design spectrum, this study establishes a system of site design spectrum coefficients to modify the Newmark design spectrum. The modified Newmark design spectrum could more realistically and reliably represent seismic features of target sites. 2. To obtain more realistic and reliable Uniform Hazard Spectrum on soil surface, this study integrates the variability of soil parameters, the nonlinear property of soils, and the vector-valued seismic site response analysis into the process of constructing Uniform Hazard Spectrum on soil surface. 3. This study investigates contribution of ground motions (i.e., tuning cases) to the uncertainty of floor response spectrum, and established the statistical relationship between t-response spectrum and ground response spectrum. Using this statistical relationship, probabilistic floor response spectrum by the direct spectra-to-spectra method considering random ground motions could be constructed. With results of this study, the most economic solution to the balance between the safety and economy is expected to reliably obtain for performance-based seismic design for the nuclear industry.