What key parameter derived from probabilistic seismic hazard analysis is crucial for determining ground motion intensity in PBSD?

The key parameter derived from probabilistic seismic hazard analysis (PSHA) that is crucial for determining ground motion intensity in performance-based seismic design (PBSD) is the uniform hazard spectrum (UHS) corresponding to a specific probability of exceedance in a given time period, or equivalently, a specific return period. PSHA produces hazard curves that relate ground motion intensity measures (like spectral acceleration at various periods) to their annual frequency of exceedance. The UHS is constructed by selecting the spectral acceleration value for a consistent probability of exceedance (e.g., 2% in 50 years, corresponding to a return period of approximately 2475 years) at each structural period of interest. This spectrum represents a uniform level of hazard across all periods, ensuring that the structure is designed to withstand ground motions with a consistent level of risk, regardless of its dynamic characteristics. Selecting a UHS allows engineers to define the seismic demand in PBSD by providing the expected spectral accelerations for a given return period, which are then used in subsequent structural analysis to verify that the design meets the required performance objectives. Thus, the UHS, derived from the PSHA hazard curves, is essential for setting the seismic design criteria in PBSD.