Uniform hazard response spectrum

The local site effects play an important role in the evaluation of seismic hazard. The proper evaluation of the local site effects will help in evaluating the amplification factors for different locations. This article deals with the evaluation of peak ground acceleration and response spectra based on the local site effects for the study area. The seismic hazard analysis was done based on a probabilistic logic tree approach and the peak horizontal acceleration (PHA) values at the bed rock level were evaluated. Different methods of site classification have been reviewed in the present work. The surface level peak ground acceleration (PGA) values were evaluatedfor the entire study area for four different site classes based on NEHRP site classification. The uniform hazard response spectrum (UHRS) has been developed for the city of Bangalore and the details are presented in this work. 

Uniform Response Spectra Uniform response spectra (UHS) represent spectral ordinates (most frequently accelerations) and are widely used in seismic norms in simplified forms, as the one shown with the continuous line in Fig. 10. Developed from PSHA, UHS is a cumulative graph (constructed from many response spectra derived from records as the one with the dashed line shown in Fig. 10 which is the outcome of a pulse-like accelerogram) that provides, for each spectral period, the spectral amplitude that has a specified probability of exceedance or return period. Therefore, the probability of exceeding a UHS is constant (or uniform) as a function of return period. In other words, a UHS represents a composite of all earthquakes that contribute to site-specific hazard curve thus, response spectra have the same statistical characteristics as the hazard curve used for their generation. Note that a UHS may not resemble the response spectrum from any specific earthquake magnitude and distance of the site. In addition, it may be too conservative for dynamic analysis and may not be appropriate for artificial ground motion generation. 

Earthquake Return Period and Its Incorporation into Seismic Actions, Fig. 14 Example of uniform response spectrum generation using probabilistic hazard maps (Adopted liomFliMA-451B (2003))... 

The strong-motion databases are also employed to select records that match a target spectrum and that can represent a response spectrum for a scenario event computed from a ground motion prediction equation or which may be derived from probabilistic seismic hazard analysis and presented as a uniform hazard spectrum (UHS) or which may be developed from building code provisions. The selected records, conveniently scaled to fit the target spectrum, are then used as input into numerical simulations for structural analysis and response site study. Several methods... 

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