Spectral acceleration

About: Spectral acceleration is a research topic. Over the lifetime, 1223 publications have been published within this topic receiving 39329 citations.

Does amplitude scaling of ground motion records result in biased nonlinear structural drift responses

Abstract: Limitations of the existing earthquake ground motion database lead to scaling of records to obtain seismograms consistent with a ground motion target for structural design and evaluation. In the engineering seismology community, acceptable limits for ‘legitimate’ scaling vary from one (no scaling allowed) to 10 or more. The concerns expressed by detractors of scaling are mostly based on the knowledge of, for example, differences in ground motion characteristics for different earthquake magnitude–distance (Mw–Rclose) scenarios, and much less on their effects on structures. At the other end of the spectrum, proponents have demonstrated that scaling is not only legitimate but also useful for assessing structural response statistics for Mw–Rclose scenarios. Their studies, however, have not investigated more recent purposes of scaling and have not always drawn conclusions for a wide spectrum of structural vibration periods and strengths. This article investigates whether scaling of records randomly selected from an Mw–Rclose bin (or range) to a target fundamental-mode spectral acceleration (Sa) level introduces bias in the expected nonlinear structural drift response of both single-degree-of-freedom oscillators and one multi-degree-of-freedom building. The bias is quantified relative to unscaled records from the target Mw–Rclose bin that are ‘naturally’ at the target Sa level. We consider scaling of records from the target Mw–Rclose bin and from other Mw–Rclose bins. The results demonstrate that scaling can indeed introduce a bias that, for the most part, can be explained by differences between the elastic response spectra of the scaled versus unscaled records. Copyright © 2007 John Wiley & Sons, Ltd.

Correlation of Response Spectral Values for Multicomponent Ground Motions

Abstract: Ground-motion prediction (attenuation) models predict the probability distributions of spectral acceleration values for a specified earthquake event. These models provide only marginal distributions, however; they do not specify correlations among spectral accelerations with differing periods or orientations. In this article a large number of strong ground motions are used to empirically estimate these cor- relations, and nonlinear regression is used to develop approximate analytical equa- tions for their evaluation. Because the correlations apply to residuals from a ground- motion prediction, they are in principle dependent on the ground-motion prediction model used. The observed correlations do not vary significantly when the underlying model is changed, however, suggesting that the predictions are applicable regardless of the model chosen by the analyst. The analytical correlation predictions improve upon previous predictions of correlations at differing periods in a randomly oriented horizontal ground-motion component. For correlations within a vertical ground mo- tion or across orthogonal components of a ground motion, these results are believed to be the first of their kind. The resulting correlation coefficient predictions are useful for a range of problems related to seismic hazard and the response of structures. Past uses of previous cor- relation predictions are described, and future applications of the new predictions are proposed. These applications will allow analysts to better understand the properties of single- and multicomponent earthquake ground motions.

Sensitivity of Building Loss Estimates to Major Uncertain Variables

Abstract: This paper examines the question of which sources of uncertainty most strongly affect the repair cost of a building in a future earthquake. Uncertainties examined here include spectral acceleration, ground-motion details, mass, damping, structural force-deformation behavior, building-component fragility, contractor costs, and the contractor's overhead and profit. We measure the variation (or swing) of the repair cost when each basic input variable except one is taken at its median value, and the remaining variable is taken at its 10th and at its 90th percentile. We perform this study using a 1960s highrise nonductile reinforced-concrete moment-frame building. Repair costs are estimated using the assembly-based vulnerability (ABV) method. We find that the top three contributors to uncertainty are assembly capacity (the structural response at which a component exceeds some damage state), shaking intensity (measured here in terms of damped elastic spectral acceleration, Sa), and details of the ground motion with a given Sa.

A New Seismic Hazard Model for New Zealand

Abstract: We present a new probabilistic seismic hazard analysis (PSHA) for New Zealand. An important feature of the analysis is the application of a new method for the treatment of historical (distributed) seismicity data in PSHA. The PSHA uses the seismicity recorded across and beneath the country to define a three-dimensional grid of a -values (i.e., parameter a of a Gutenberg-Richter distribution log N/yr = a - bM , in which N /yr is the number of earthquakes per year recorded inside each grid cell equal to or greater than magnitude M ); parameter b and the limiting maximum cutoff magnitude of the Gutenberg-Richter distribution are defined from the surrounding region (14 crustal and 23 subcrustal seismotectonic zones are defined for the country) and then smoothed across the boundaries of the zones. The methodology therefore combines the modern method of defining continuous distributions of seismicity parameters (Frankel, 1995; Frankel et al. , 1996) with the traditional method of defining large area sources and the associated seismicity parameters (e.g., Algermissen et al. , 1990). The methodology provides a means of including deep (subduction zone) seismicity in a PSHA, preserves the finer-scale spatial variations of seismicity rates across a region, avoids the undesirable edge effects produced in the traditional method when adjacent area sources enclose areas of significantly different seismicity rates, and also enables parameters most reliably defined at a regional scale (parameter b and maximum cutoff magnitude of a Gutenberg-Richter distribution, and slip type) to be incorporated into the PSHA. The PSHA combines the modeled seismicity data with geological data describing the location and earthquake recurrence behavior of 305 active faults and new attenuation relationships for peak ground acceleration and spectral acceleration developed specifically for New Zealand. Different attenuation expressions are used for crustal and subduction zone earthquakes. The resulting PSH maps for a 150-year return period show the highest hazard to occur in the center and southwest of the country, in the areas of highest historical crustal and deep subduction zone seismicity. In contrast, the longer return-period maps (475 and 1000 year return period) show the highest hazard to occur from the southwest to northeast ends of the country, along the faults that accommodate the majority of the motion between the Pacific and Australian plates. The maps are currently being used to revise New Zealand's building code, which has previously been based on PSHAs that did not explicitly include individual faults as earthquake sources. Manuscript received 10 April 2001.