Estimated Peak Ground Acceleration Research Articles

Actuator Saturation and Control Design for Buildings under Seismic Excitation

Efficient design techniques are presented for improving the response of seismic-excited buildings under actuators with limited capacity. Information regarding the actuator capacity and estimated peak ground acceleration is used to fine tune the controller and reduce conservatism. Both state feedback and observer-based controllers are discussed. The observer-based controller uses the measurement of the ground acceleration, though this requirement can be removed easily. Sufficient conditions for feasibility of a feedback controller are expressed in terms of linear matrix inequalities. Performance of the proposed techniques is illustrated through simulations of a six-story building subject to earthquake ground motion.

Rocking Response of Free-Standing Blocks under Cycloidal Pulses

This paper examines in depth the transient rocking response of free-standing rigid blocks subjected to physically realizable trigonometric pulses. First, the expressions for the dynamic horizontal and vertical reactions at the pivot point of a rocking block are derived and it is shown that the coefficient of friction needed to sustain pure rocking motion is, in general, an increasing function of the acceleration level of the pulse. Subsequently, this paper shows that under cycloidal pulses a free-standing block can overturn with two distinct modes: (1) by exhibiting one or more impacts; and (2) without exhibiting any impact. The existence of the second mode results in a safe region that is located on the acceleration-frequency plane above the minimum overturning acceleration spectrum. The shape of this region depends on the coefficient of restitution and is sensitive to the nonlinear nature of the problem. This paper concludes that the sensitive nonlinear nature of the problem, in association with the presence of the safe region that embraces the minimum overturning acceleration spectrum, complicates further the task of estimating peak ground acceleration by only examining the geometry of free-standing objects that either overturned or survived a ground shaking.

“Site & region-specific” response spectra: a probabilistic approach

Design seismic forces depend on Peak Ground Acceleration (PGA) values and on the shape of Response Spectrum (RS) curves dictated by Building Codes or which need to be evaluated in every particular case. The PGA values and RS curves strictly depend on earthquake magnitude and distance, as well as on the regional and local geological conditions. At present, there is no doubt that it is necessary to construct so-called “Site & Region-specific” Building Code provisions reflecting the influence of different magnitude events at different distances that may occur during the life time of the construction, as well as the variety of local ground conditions. A scheme of Uniform Hazard Response Spectra and PGA estimation considering local site response is described in this paper. The assessments of these design parameters are obtained on the basis of Uniform Hazard Fourier spectra using the conception of “dominant earthquakes”. The effect of local geology is included by means of the soil/reference site spectral ratios.

Faulting, shallow seismicity and seismic hazard analysis for the Costa Rican Central Valley

Faulting, shallow seismicity (0–30km), and seismic hazard of the Costa Rican Central Valley were analyzed. Faults in the study area are oriented northwest or northeast. There is an active fault system in the south flank of the Central Volcanic Ridge and another in the north flank of the Talamanca Ridge. Faults of these systems have generated 15 destructive earthquakes in the area during the last 228 years all of them shallow and their locations show one cluster near the Poas Volcano and another southward the Central Valley. These earthquakes have damaged cities of the Central Valley, two of them destroyed Cartago city and almost 1000 people were killed. Regarding recent seismicity, there are three main seismic sources at the Central Volcanic Ridge: Irazu, Bajo de la Hondura and Poas and other three in the Talamanca Ridge: Puriscal, Los Santos and Pejibaye.A seismic hazard map for the Metropolitan Area of San José has been elaborated, based on local tectonic and seismic information. The area for the hazard computation covers an area of 20×15km2 and includes the zone where the most population and socioeconomic activities are concentrated. The computation analysis are based on areas zones and faults, each one characterized by recurrence parameters, geometry, minimum and maximum magnitude and source depth. A recent local spectral attenuation model, which includes relations for shallow crustal sources and subduction zone earthquakes, has been applied in this study. The seismic hazard results are presented in terms of contour plots of estimated peak ground acceleration (PGA) for bedrock conditions for return period of 50, 100 and 500 years. In the Central Park of San Jose City the following PGA values were found: 0.29g for 50 years, 0.36g for 100 years, and 0.53g for 500 years.

Hazard-Consistent Ground Motions: Generation on the Basis of Uniform Hazard Fourier Spectra

Design seismic forces depend on peak ground acceleration (PGA) values and on the shape of response spectra (RS) dictated by building codes or that need to be evaluated on a site-specific basis. The PGA values and RS strictly depend on earthquake magnitude and distance, style of faulting and in cases, near-source effects (e.g., rupture directivity), as well as on the regional and local geological conditions. At present, there is no doubt that it is necessary to construct so-called site- and region-specific building code provisions reflecting the influence of different magnitude events at different distances that may occur during the lifetime of the construction, as well as the variety of local ground conditions. A scheme of Uniform Hazard Response Spectra and PGA estimation considering local site response is described in this article. The assessments of these design parameters are obtained on the basis of Uniform Hazard Fourier spectra using the concept of “dominant earthquakes”. The effect of local geology is included by means of the soil/reference site spectral ratios. The results of using the method are presented for the regions characterized by different seismicity and tectonics and compared with the data obtained during the recent strong earthquakes: the Caucasus (Armenia, the 1988 Spitak earthquake region) and the Turan Plate (Central Asia, the 1979 and 1984 Gazli earthquakes region).

Seismic hazard assessment of Iran

The development of the new seismic hazard map of Iran is based on probabilistic seismic hazard computation using the historical earthquakes data, geology, tectonics, fault activity and seismic source models in Iran. These maps have been prepared to indicate the earthquake hazard of Iran in the form of iso-acceleration contour lines, and seismic hazard zoning, by using current probabilistic procedures. They display the probabilistic estimates of Peak Ground Acceleration (PGA) for the return periods of 75 and 475 years. The maps have been divided into intervals of 0.25 degrees in both latitudinal and longitudinal directions to calculate the peak ground acceleration values at each grid point and draw the seismic hazard curves. The results presented in this study will provide the basis for the preparation of seismic risk maps, the estimation of earthquake insurance premiums, and the preliminary site evaluation of critical facilities.

Dynamic site response evaluation of the Port City of Aqaba (Jordan) employing the equivalent linear method

As part of an ongoing research program to develop local seismic engineering ground motion parameters for implementation in the Jordanian Seismic Building Code, a practical contribution is made to determine the local site coefficient (S) for the Port City of Aqaba, southern Jordan. Employing probabilistic peak ground acceleration estimates using FRISK, the overall dynamic site response design spectrum is obtained through the calculated response spectrum based on selected soil-rock column profiles applying SHAKE91. The parabolic shape of the S coefficient design spectrum is given by the following relationships:S = 1.06 for Tb/ Ts<= 0.56S = -0.81 + 4.68(Tb/ Ts) -2.38(Tb/ Ts)2for 0.56 < (Tb/ Ts)<=1.43S = 1.00 for Tb/ Ts>1.43where Tband Tsare the structural and site response design periods (in seconds), respectively.Key words: dynamic, site, response, Aqaba, spectrum, design.

Dynamic site response evaluation of the Port City of Aqaba (Jordan) employing the equivalent linear method

As part of an ongoing research program to develop local seismic engineering ground motion parameters for implementation in the Jordanian Seismic Building Code, a practical contribution is made to determine the local site coefficient (S) for the Port City of Aqaba, southern Jordan. Employing probabilistic peak ground acceleration estimates using FRISK, the overall dynamic site response design spectrum is obtained through the calculated response spectrum based on selected soil-rock column profiles applying SHAKE91. The parabolic shape of the S coefficient design spectrum is given by the following relationships:S = 1.06 for Tb / Ts <= 0.56S = -0.81 + 4.68(Tb / Ts) -2.38(Tb / Ts)2 for 0.56 < (Tb / Ts)<=1.43S = 1.00 for Tb / Ts >1.43where Tb and Ts are the structural and site response design periods (in seconds), respectively.Key words: dynamic, site, response, Aqaba, spectrum, design.

Semi-empirical estimation of peak ground acceleration from large Earthquakes : Midorikawa S. TectonophysicsV218, N1/3, Feb 1993, P287–295

Semi-empirical estimation of peak ground acceleration from large Earthquakes : Midorikawa S. TectonophysicsV218, N1/3, Feb 1993, P287–295

Semi-empirical estimation of peak ground acceleration from large earthquakes

A simplified method is proposed for synthesizing ground acceleration from a large earthquake. The present method is based on the semi-empirical method of Irikura (1986), which is consistent with the ω-square source model, but is much simplified for engineering use. In this method the fault of the large earthquake is divided into small elements and the acceleration envelope waveforms, instead of the time histories, from the elements are simply determined using the empirical relations. The envelope waveforms from the elements are summed to synthesize the envelope waveform of a large earthquake. The peak acceleration of the large earthquake is obtained from the maximum value of the summed envelope. To test the present method, the peak accelerations are calculated for the 1985 Central Chile earthquake ( M s 7.8), during which a considerable number of the strong-motion records were obtained close to the source. The calculated accelerations are in good agreement with the observed ones. The attenuation characteristics of the calculated peak accelerations for earthquakes of different magnitudes are examined. The results show that: 1. (1) the shortest distance from the fault plane is an appropriate definition for source distance; 2. (2) the peak acceleration becomes independent of magnitude in the near-field; and 3. (3) the source direction effect on the peak acceleration is not negligible.

Empirical Methods for the Prediction of Response Spectra

Three empirical methods of estimating response spectra are reviewed. It is shown that these methods produce comparable results, provided that the comparisons are made in a consistent manner. Although the traditional method of scaling amplification factors by peak ground motions is fundamentally reasonable, there exist some significant discrepancies between scaled and other types of spectra. The basic reason for this is that the amplification factors commonly used in the engineering community are biased toward those of a large magnitude earthquake recorded on a soil site. The dependence of spectral shape on magnitude and site conditions can be accounted for by independent estimates of peak ground acceleration, velocity and displacement to scale an unbiased set of amplification factors derived for particular site conditions. Other methods of estimating spectra account for the dependence of spectral shape on magnitude and site conditions in a more direct manner. In order to reduce the discrepancies between scaled and other types of spectra, it is recommended that a new set of amplification factors be estimated using a suite of response spectra due to earthquakes whose magnitudes are evenly distributed in the range 5.0 ≤ M ≤ 7.5 and which have been recorded on sites having similar soil conditions.