Query: ground motion taiwan 1999

title: SSI effects on ground motion at Lotung LSST Site
abstract: A 3D finite element model is developed to study soil structure interaction (SSI) effects at a Large Scale Seismic Test (LSST) site in Lotung, Taiwan, during the earthquake of May 20, 1986. Analyses are carried out by direct method incorporating a 1/4 scale nuclear plant containment structure. The containment structure is modeled as a linearly elastic material, while the subsoil is modeled as an elastoplastic continuum material that deforms plastically according to a bounding surface plasticity theory with a vanishing elastic region. Eigenvalue analyses are performed to see how the presence of the structure affects the fundamental frequencies and modes of vibration of the system in the limit of elastic response. SSI effects are shown to be partly responsible for the reduced peak north south ground surface acceleration recorded by a downhole array near the containment structure. Eigenvalue studies suggest that the local effect of the containment structure is to generate rocking and torsional vibration modes, in addition to the usual lateral and vertical modes. However, results of time domain studies indicate that the former modes (rocking and torsional) were not triggered by the 1986 earthquake.

title: NONLINEAR GROUND RESPONSE AT LOTUNG LSST SITE
abstract: A fully nonlinear finite element (FE) model is developed to investigate the impact of hysteretic and viscous material behavior on the downhole motion recorded by an array at a large scale seismic test site in Lotung, Taiwan, during the earthquake of May 20, 1986. A stick model with the same spatial interpolation accuracy as a three dimensional FE model is used for vertical wave propagation analysis. The constitutive model is based on a three dimensional bounding surface plasticity theory with a vanishing elastic region, and accounts for shear stiffness degradation right at the onset of loading. The model is cast in a time domain nonlinear FE code SPECTRA and is used to analyze the 1986 earthquake data. It is shown that the recorded downhole motion of Lotung was dominated by nonlinear response. Results of the fully nonlinear analysis are compared with the predictions of the program SHAKE so that the performance of the nonlinear model may be assessed relative to that of an equivalent linear model.

title: Spatial ground motion effect on relative displacement of adjacent building structures
abstract: This paper analyses earthquake ground motion spatial variation effects on relative linear elastic response of adjacent building structures. It studies the relative importance of ground motion spatial variations and dynamic characteristics of adjacent structures in causing relative responses. Random vibration method is used in the study. It is found that, besides ground acceleration induced dynamic responses, quasi static responses induced by spatially varying ground displacements also contribute significantly to the relative structural responses. The effects of spatial ground motions are very pronounced to the relative displacements of adjacent low rise structures, and to those of high rise adjacent structures with similar vibration characteristics. The effect of vibration properties of adjacent structures are, however, more significant to those of high rise adjacent structures if they poses noticeably different vibration periods.

title: Dynamic geometrical effects on strong ground motion in a normal fault model
abstract: We report results of measurement of particle motion in a foam rubber model of normal faulting and compare the results with similar results for a strike slip geometry. Standard computer modeling of strong ground motion from normal fault earthquakes has used dislocation theory, in which slip along the shallow part of the fault is prescribed by assuming particular time functions for fault slip. Unfortunately, in the case of normal faults, there are essentially no near fault data from large earthquakes to constrain the modeling. In an extensional faulting regime the static normal and shear stresses along the fault must approach zero at the surface, and thus the upper few kilometers of the fault have inherently less stored strain energy than the maximum possible for strike slip faults. In addition there are dynamic effects from geometry and drop in fault normal stress which affect the fault motion. Physical models of faulting, such as foam rubber modeling, are guaranteed to obey static and dynamic mechanical laws and thus can be used to gain insight into the physical processes involved. In this study we compare surface accelerations from normal fault and strike slip geometries. The data show surface accelerations near the normal fault trace that are systematically lower, by anmore average factor of about 0.1, compared to the accelerations at the side sensors, which represent strike slip motion. These results suggest that kinematic modeling of ground motion using classical dislocation techniques is inappropriate on the shallow part of the fault. The results of this study are qualitatively similar to those obtained for numerical models, such as a dynamic lattice model {ital Shi} {ital et al. 1997] and a finite element model {ital Oglesby} {ital et al. 1998] lending support to the probability that similar effects take place in the real Earth.

title: Influence of ground motion intensity on the effectiveness of tuned mass dampers
abstract: The effectiveness of Tuned Mass Dampers (TMD) on buildings subjected to moderate and high intensity motions is analysed. First, the response of a 22 storey four bay reinforced concrete non linear frame with a TMD is studied for motions with different intensities. Several values of the relevant parameters are assumed in the analyses. Then, equivalent single degree of freedom systems with TMDs and without them are defined and analysed under the action of ground motions with intensities associated with different return intervals at the site where the structures are located. Vulnerability curves for the systems are obtained based on the probabilities of reaching two different performance limit states. The expected annual rate of exceedance of each limit state is calculated. The results show that the effectiveness of TMDs is higher for systems with small non linearity produced by small and moderate earthquakes, than for systems with high non linear behaviour, generally associated with high intensity motions. Some recommendations about the applicability of TMD are given.

title: EXAMINATION OF SELECTED RECENT GROUND MOTION RECORDS FROM TURKEY IN TERMS OF DISPLACEMENT DESIGN PROCEDURES
abstract: Selected near source records obtained from the 17 August and 12 November 1999 events in Turkey are studied. The records are corrected using different schemes for their effect on displacement based design tools. One of these correction procedures is thought to be suitable for the near source ground motion characteristics. The results indicate that even significant differences in the displacement traces would not be vital for the dynamic analysis of ordinary structures. However, they might be important for buildings equipped by dampers. The consistency of the effective damping concept for modifying the elastic ADRS curves in the capacity spectrum is examined. Near source ground motions demand large drifts for a wider range of periods. This underscores the importance of displacement based design procedures. The results show that the proposed damping factors for the modification of elastic spectrum does not give reliable estimates in the non linear range. Further research is required in this area to consider the requirements imposed by near source ground motions.

title: Implications of the Rupture Process from the Displacement Distribution of Strong Ground Motions Recorded during the 21 September 1999 Chi Chi,Taiwan Earthquake
abstract: The IPEI payload onboard ROCSAT 1 has observed many well knownlow latitude ionospheric phenomena at 600 km altitude,such as the diurnalvariations of ion density,composition and temperature.The equatorialspread F events,such as bubbles and blobs,together with the flow variationsare also recorded with an unprecedented high time resolution at asampling rate of 1024 Hz.The satellite borne data on power spectral densityof the equatorial spread F event on the transitional scale(10 100m)ispresented here for the first time.The local time and longitudinal variationsof the vertical drift velocity in the dawn sector indicated strong hemi spheric asymmetry.

title: Capacity spectrum method based on inelastic demand spectra
abstract: By means of a graphical procedure, the capacity spectrum method compares the capacity of a structure with the demands of earthquake ground motion on it. In the present version of the method, highly damped elastic spectra have been used to determine seismic demand. A more straightforward approach for the determination of seismic demand is based on the use of the inelastic strength and displacement spectra which can be obtained directly by time history analyses of inelastic SDOF systems, or indirectly from elastic spectra. The advantages of the two approaches (i.e. the visual representation of the capacity spectrum method and the superior physical basis of inelastic demand spectra) can be combined. In this paper, the idea of using inelastic demand spectra within the capacity spectrum method has been elaborated and is presented in an easy to use format. The approach represents the so called N2 method formulated in the format of the capacity spectrum method. By reversing the procedure, a direct displacement based design can be performed. The application of the modified capacity spectrum method is illustrated by means of two examples.

title: Response of buildings to near field pulse like ground motions
abstract: Ground motions affected by directivity focusing at near field stations contain distinct pulses in acceleration, velocity, and displacement histories. For the same Peak Ground Acceleration (PGA) and duration of shaking, ground motions with directivity pulses can generate much higher base shears, inter storey drifts, and roof displacements in high rise buildings as compared to the 1940 El Centro ground motion which does not contain these pulses. Also, the ductility demand can be much higher and the effectiveness of supplemental damping lower for pulse like ground motions. This paper presents a simple interpretation of the response characteristics of three recorded and one synthetic near field ground motions. It is seen that for pulse like ground motions similar to any other ground motion the Peak values of Ground Acceleration, Velocity, and Displacement (PGA, PGV and PGD) are the key response parameters. Near field ground motions with directivity effects tend to have high PGV/PGA ratio, which dramatically influences their response characteristics.

title: Effect of baseline corrections on response spectra for two recordings of the 1999 Chi Chi, Taiwan, earthquake
abstract: 1999 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.  Displacements derived from the accelerogram recordings of the 1999 Chi Chi, Taiwan earthquake at stations TCU078 and TCU129 show drifts when only a simple baseline derived from the pre event portion of the record is removed from the records. The appearance of the velocity and displacement records suggests that changes in the zero level of the acceleration are responsible for these drifts. The source of the shifts in zero level are unknown, but might include tilts in the instruments or the response of the instruments to strong shaking. This note illustrates the effect on the velocity, displacement, and response spectra of several schemes for accounting for these baseline shifts. The most important conclusion for earthquake engineering purposes is that the response spectra for periods less than about 20 sec are unaffected by the baseline correction. The results suggest, however, that static displacements estimated from the instruments should be used with caution. Although limited to the analysis of only two recordings, the results may have more general significance both for the many other recordings of this earthquake and for data that will be obtained in the future from similar high quality accelerograph networks now being installed or soon to be installed in many parts of the world. The digital accelerograph installed and maintained by Central Weather Bureau in Taiwan produced a rich set of records from the September 20, 1999 M 7.6 Chi Chi, Taiwan earthquake and its aftershocks (Shin et al. 2000) This earthquake has produced the most complete set of strong motion recordings ever obtained. The data were obtained from Teledyne Geotech Model A900 digital accelerographs, with 2 g gain and 16 bit resolution, recorded at 200 samples per second. The transducers are flat to acceleration from dc to 50 Hz. The system uses a trigger algorithm and a buffer so that the pre trigger part of the ground motion is preserved. At this time data from only two stations have been released (Lee, 1999) but the features found in the analysis of these records are probably not restricted 1 to those records. The stations for which data have been released are TCU078 and TCU129. These stations are within