Level peak ground acceleration

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. 

Failure frequencies of structures, equipment, and piping are related to their acceleration which is related to the ground-motion of the plant s foundation (e.g., the peak ground acceleration). For PSA, it is useful to present the seismic hazard at the site as a family of hazard curves with different nonexceedence-probability levels (Figure 5.1-3). By selecting various values of the peak ground acceleration, the acceleration and forces on the plant components may be obtained as described in the following. 

Figure 6.9 summarizes the result of Equation (6.87) for site class A. The six curves (from top to bottom) show the log o PGA versus the magnitude of earthquake M for six levels of distance, namely 10, 50, 100, 250, 500 and 1000 km. This chart can be used for prediction of peak ground acceleration in the design process. One first estimates the closest fault from the site so the corresponding curve can be selected. This curve shows the estimated peak ground acceleration under different levels of earthquake, which may be estimated by neural networks [194]. 

For the deterministic scenarios, we considered three simulated artificial earthquakes with different Peak Ground Accelerations. Based on different levels of the PGA, we can make different seismic scenarios regarding the degree of damage of the buildings in a selected area of the city, presented in Fig. 5.1. 

Regardless of the exposure to seismic hazard, an SI 2 design basis earthquakes should be adopted for every nuclear power plant for the design of safety classified items. The minimum level should correspond to a peak ground acceleration of O.lg (zero period of the design response spectrum), to be considered at the free field. A unified, site compatible spectrum should be associated with this peak ground acceleration value. In this case SL-1 may be assumed to be coincident with SL-2. 

The regional earthquake hazard scenario can be probabilistic or deterministic. The variation of earthquake ground shaking parameters (peak ground accelerations, PGA and spectral accelerations, SA at T = 0.2 s and 1 s at the engineering bedrock outcrop) are determined independently within the investigated area for a specified level of exceedance probability or based on deterministic simulations. 

Local Magnitude ML Typical peak ground acceleration a near the vicinity of the fault rupture Typical duration of ground shaking near the vicinity of the fault rupture Modified Mercalli intensity level near the vicinity of the fault rupture... 

Design earthquake Peak ground acceleration PGA (bedrock level or fill level), earthquake magnitude M. Alternatively the Contractor can be instructed to perform a site specific seismic study ... 

As shown in Fig. 8, a seismic hazard curve represents the mean annual rate of exceedance of a particular ground motion parameter (peak or spectral accelerations, etc.). In other words, the vertical axis provides the (desired) level of probability, while the horizontal axis depicts a ground motion parameter, such as peak ground acceleration. A seismic hazard curve is the ultimate result of a PSHA after combining all uncertainties and performing necessary probability computations. Contribution of independent sources can be interpreted in different seismic hazard curves (to illustrate which sources are more important) together with the total seismic... 

The above hazard levels can be associated to major seismic demand parameters, such as the peak ground acceleration (PGA). For instance, in the study by Papazachos et al. (1993), Greece was divided into four zones, and based on this work. Table 3 depicts the PGA levels for two return periods, Tr, utilizing the following log-linear formula ... 

If the exponent k ( slope of the hazard curve Aa(<2g) in a log-log plot) is about constant, two peak ground acceleration levels Ogi, Og2, corresponding to two different mean return periods, rR(agi), are related as... 

EN-Eurocode 8 adopts the same spectral shape for the different seismic actions to be used at different performance levels or purposes. The difference in the hazard level is reflected only through the peak ground acceleration to which the spectrum is anchored. 

---