Strong Motion Characteristics Research Articles

The effect of material and ground motion uncertainty on the seismic vulnerability curves of RC structure

Starting from the premise that vulnerability curves are an indispensable ingredient of earthquake loss assessment, this paper focuses on establishing the relative effect of strong-motion variability and random structural parameters on the ensuing vulnerability curves. Moreover, the effect of the selection of statistical models used to present simulation results is studied. A three story ordinary moment resisting reinforced concrete frame, previously shake-table tested, is used as a basis for the fragility analysis. The analytical environment and the structural model are verified through comparison with shaking-table test results. The selection of ground motion sets, definition of limit states, statistical manipulation of simulation results, and the effect of material variability are investigated. No approximations are used to reduce the sample size or minimize the analytical effort, in order that attention is focused on the parameters under investigation. Notwithstanding the limited scope of the study, the results presented indicate that the effect of randomness in material response parameters is far less significant than the effect of strong-motion characteristics. Therefore, the importance of scrupulous selection and scaling of strong-motion and use of appropriate limit states and statistical models is emphasized.

Neural network estimation of ground peak acceleration at stations along Taiwan high-speed rail system

It is essential to understand the characteristics of strong motion for reducing the negative impacts in a high-risk area. In this work, a combination of seismic parameters including epicentral distance, focal depth, and magnitude from historical records at 30 checking stations were used in back-propagation neural network model, to estimate peak ground acceleration at ten train stations along the high-speed rail system in Taiwan. The estimation was verified with available microtremor measurement at a specified station, and the calculated horizontal acceleration was checked with the existing building code requirements. A potential hazardous station was identified from the neural network estimation, which exhibited a significantly higher acceleration than that of the design value. The obtained results might be useful for revising the currently applied building code at this region to further fit in the actual earthquake response.

Northridge Earthquake Effects on Pipelines and Residential Buildings

This article is focused on the spatial variability of earthquake strong motion and its relationship with the performance of water-distribution pipelines provided by Los Angeles Department of Water and Power (ladwp) and residential buildings. Analyses of strong-motion characteristics and their correlations with pipeline and building damage were conducted with an immense geographical information system (gis) database for the 1994 Northridge earthquake, which was collected, digitized, and organized by researchers at Cornell. There are statistically significant correlations among pipeline repair rate (repairs/km) and peak ground velocity (pgv) for cast iron, ductile iron, asbestos cement, and steel pipe. Statistically significant regressions have been developed between damage ratio, dr (percent of existing structures with damage equal to or exceeding a particular damage factor, df [percent of building replacement cost]) and the magnitudes of seismic parameters, such as pgv and spectrum intensity (si). Regressions developed between dr and scaled seismic parameters (seismic parameters normalized with respect to df) resulted in predictive equations having a very high degree of statistical significance. Algorithms to visualize damage patterns for buildings were developed and validated to choose optimal gis mesh dimensions and contour intervals. Ordinary kriging was used to develop regressions of pipeline repair rate and residential building dr associated with 90% confidence pgv and spectrum intensity (weighted average pseudovelocity). Such regressions provide an explicit means of characterizing the uncertainty embodied in the strong-motion data.

Reconnaissance Report on the 31 March 2002 Earthquake on the East Coast of Taiwan

On 31 March 2002, an earthquake of magnitude ML=6.8 occurred in northeastern Taiwan that caused five deaths and damage to more than 300 buildings. The earthquake left some important lessons; these lessons were not considered after the 1999 Chi-Chi (Taiwan) earthquake but must be taken into account for the management of a similar situation in the future. This article first presents the strong motion characteristics found from the ground accelerations recorded from this event. In particular, the basin effects on the distribution of ground motion intensities observed in Taipei Basin are critically reviewed. Observations of some severe building damage following the earthquakes are then summarized. The building damage modes for this event, particularly due to the basin effect, are explored in detail. The characteristics of the building disaster reflected a typical situation that can occur in cities located in high seismic risk. Finally, the collapse of the two tower cranes on, and its impact on, the Taipei Financial Center construction site are described in detail. This article presents the main lessons learned from this earthquake in the light of work performed by the research team for natural disaster from the National Center for Research on Earthquake Engineering, Taiwan.

Neural networks approach and microtremor measurements in estimating peak ground acceleration due to strong motion

Peak ground acceleration is a very important factor that must be considered in construction site for examining the potential damage resulting from earthquake. The actual records by seismometer at stations related to the site may be taken as a basis, but a reliable estimating method may be useful for providing more detailed information of the strong motion characteristics. Therefore, the purpose of this study was by using back-propagation neural networks to develop a model for estimating peak ground acceleration at two main line sections of Kaohsiung Mass Rapid Transit in Taiwan. Additionally, the microtremor measurements with Nakamura transformation technique were taken to further validate the estimations. Three neural networks models with different inputs including epicentral distance, focal depth and magnitude of the earthquake records were trained and the output results were compared with available nonlinear regression analysis. The comparisons exhibited that the present neural networks model did have a better performance than that of the other methods, as the calculation results were more reasonable and closer to the actual seismic records. Besides, the distributions of estimating peak ground acceleration from both of computations and measurements might provide valuable information from theoretical and practical standpoints.

The Simulation of Ground Motions Using Envelope Summations

— The technique of Midorikawa (1993) has been modified to obtain a resultant envelope function at the observation point by placing the rupture causing an earthquake in a layered earth model. The method and its dependency on various modelling parameters are studied in detail. The complete study shows that the generated resultant envelope follows important strong motion characteristics such as directivity and attenuation effects. The simulated resultant envelope is further used for generating synthetic accelerograms by multiplying filtered white noise with the envelope of accelerogram at a particular observation point. Filters through which white noise passes include the effects of geometrical spreading, anelastic attenuation and near-site attenuation at high frequencies.¶Uttarkashi earthquake is among few Indian earthquakes for which strong motion data are available at thirteen different stations. Using the technique presented in this work, envelope function as well as complete acceleration time history during Uttarkashi earthquake has been simulated at these observation points. Comparison of peak acceleration, duration and acceleration response spectra confirms the utility and efficacy of the approach.

Refined force reduction factors for seismic design

Whereas seismic design based on deformations is a concept that is gaining ground, existing codes are fundamentally force-based, with a final check on deformations. A central feature of force-based seismic design is the response modification factor ( R or q). Many studies have attempted to quantify the potential of structural systems to delimit the level of force imposed by virtue of their ductility and energy absorption capacity. This paper employs a well controlled and evenly distributed earthquake data-set (in magnitude, distance and site characterization spaces) to derive values for force reduction factors needed for the structure to reach, and not exceed, a pre-determined level of ductility. It is observed that the force modification factors are only slightly influenced by the shape of the hysteretic model used in their derivation and even less sensitive to strong motion characteristics. A linear representation is recommended for use in a benchmark for ‘demand’ considerations and given in an easy-to-use parametric form.

Interdependency between seismic acceleration parameters and the behaviour of structures

The first part of this article describes some strong motion acceleration parameters of seismic excitations. Furthermore, a classification of the ground motions at a site according to their damage potential is presented. The second part deals with a nonlinear dynamic analysis of a six storey reinforced concrete plane frame. Damage indicators in the form of cross sectional ductility demand are evaluated and correlated with the strong motion characteristics. The aim is to extract among the several seismic parameters, those which have drastic affection on the damage indicators of the structures. The attention is focused on earthquake acceleration time histories, recorded in Greece, Central and North America, which are well-known sites with strong seismic activity.

Seismic Response of Liquefaction Sites

The authors of this technical paper focus on the seismic response of liquefaction sites by evaluating the transient shear strains and strong-motion characteristics at Treasure Island during the 1989 Loma Prieta earthquake. The strain levels are used to model soil and buried pipeline deformations observed in the Marina District of San Francisco during the same earthquake. The authors found that transient strains play a critical role in lifeline performance, based on the favorable comparisons of predicted and observed pipeline damage. A simple model for liquefaction sites reveals that shear modulus reduction caused by increased pore pressure can amplify either acceleration or transient displacement, depending on soil properties and deposit thickness. Liquefaction of thick, loose sand deposits can attenuate accelerations while amplifying long-period displacements. The model offers a quantitative means of characterizing the phenomenon of ground oscillation that has been noted at liquefaction sites.

The slip history of the 1994 Northridge, California, earthquake determined from strong-motion, teleseismic,GPS, and leveling data

AbstractWe present a rupture model of the Northridge earthquake, determined from the joint inversion of near-source strong ground motion recordings, P and SH teleseismic body waves, Global Positioning System (GPS) displacement vectors, and permanent uplift measured along leveling lines. The fault is defined to strike 122° and dip 40° to the south-southwest. The average rake vector is determined to be 101°, and average slip is 1.3 m; the peak slip reaches about 3 m. Our estimate of the seismic moment is 1.3 ± 0.2 × 1026 dyne-cm (potency of 0.4 km3). The rupture area is small relative to the overall aftershock dimensions and is approximately 15 km along strike, nearly 20 km in the dip direction, and there is no indication of slip shallower than about 5 to 6 km. The up-dip, strong-motion velocity waveforms are dominated by large S-wave pulses attributed to source directivity and are comprised of at least 2 to 3 distinct arrivals (a few seconds apart). Stations at southern azimuths indicate two main S-wave arrivals separated longer in time (about 4 to 5 sec). These observations are best modeled with a complex distribution of subevents: The initial S-wave arrival comes from an asperity that begins at the hypocenter and extends up-dip and to the north where a second, larger subevent is centered (about 12 km away). The secondary S arrivals at southern azimuths are best fit with additional energy radiation from another high slip region at a depth of 19 km, 8 km west of the hypocenter. The resolving power of the individual data sets is examined by predicting the geodetic (GPS and leveling) displacements with the dislocation model determined from the waveform data, and vice versa, and also by analyzing how well the teleseismic solution predicts the recorded strong motions. The general features of the geodetic displacements are not well predicted from the model determined independently from the strong-motion data; likewise, the slip model determined from geodetic data does not adequately reproduce the strong-motion characteristics. Whereas a particularly smooth slip pattern is sufficient to satisfy the geodetic data, the strong-motion and teleseismic data require a more heterogeneous slip distribution in order to reproduce the velocity amplitudes and frequency content. Although the teleseismic model can adequately reproduce the overall amplitude and frequency content of the strong-motion velocity recordings, it does a poor job of predicting the geodetic data. Consequently, a robust representation of the slip history and heterogeneity requires a combined analysis of these data sets.

地震観測に基づく観測点特性と径路減衰特性の評価

Estimation of site factor and propagation characteristics is an important work in order to evaluate strong-motion characteristics. This paper gives a review of methods used for the estimation of these two factors. The usual evaluation of site factor is based on the records obtained by means of downhloe array observation. Several methods which are independent of downhole array recordings have appeared in the last decade in order to evaluate the site factor. Most methods have essentially an inversion scheme, and are applicable to the separation of site factor, propagation characteristics and source factor, simultaneously. In this review, coda normalization method, method by using a spectral decay parameter and direct deconvolution method are given as such methods.

Earthquake Ground Motions: Implications for Designing Structures and Reconciling Structural Damage

Until recently, characteristics of strong ground motion resulting from different soil conditions were considered the dominant factor in developing design ground motions and reconciling observed damage. Interpretation of recent recordings of earthquakes by strong motion instrument arrays installed in California and Taiwan show that basic characteristics of strong motion are greatly influenced by the seismological and geological conditions. For a given soil condition, the characteristics of strong ground motion (peak ground acceleration, peak ground velocity, peak ground displacement, duration, spectral content, and time histories) can vary significantly whether the site is near or far from the seismic source. As local soil conditions only modify the ground motions produced by a given source, variability in ground motion due to seismologic and geologic conditions (for a given soil condition) must be considered in estimating earthquake ground motions for structural design or for estimating structural vulnerabilities to reconcile earthquake-related damage.

Research needs associated with seismic load on nuclear power plants

A research program aimed at providing the desired level of seismic resistance of nuclear power plants in a cost-effective manner is proposed. The results of such a research program would provide direct measurement of seismic design parameters associated with loadings which closely simulate real strong motion characteristics on major structural and mechanical systems.