Showing papers by "National Center for Research on Earthquake Engineering published in 2000"

Ground motion characteristics of the Chi‐Chi earthquake of 21 September 1999

Abstract: The purpose of this paper is to investigate the ground motion characteristics of the Chi-Chi earthquake (21 September 1999) as well as the interpretation of structural damage due to this earthquake. Over 300 strong motion records were collected from the strong motion network of Taiwan for this earthquake. A lot of near-field ground motion data were collected. They provide valuable information on the study of ground motion characteristics of pulse-like near-field ground motions as well as fault displacement. This study includes: attenuation of ground motion both in PGA and spectral amplitude, principal direction, elastic and inelastic response analysis of a SDOF system subjected to near-field ground motion collected from this event. The distribution of spectral acceleration and spectral velocity along the Chelungpu fault is discussed. Based on the mode decomposition method the intrinsic mode function of ground acceleration of this earthquake is examined. A long-period wave with large amplitude was observed in most of the near-source ground acceleration. The seismic demand from the recorded near-field ground motion is also investigated with an evaluation of seismic design criteria of Taiwan Building Code. Copyright © 2000 John Wiley & Sons, Ltd.

Design of dampers for structures based on optimal control theory

Abstract: SUMMARY The aim of this paper was to propose a design guideline for using visco-elastic dampers for the control of building structures subjected to earthquake loading as well as suspension roof structures subjected to wind loading. The active control algorithm was used to calculate the control forces. Based on the single-mode approach the control forces were transformed to the forces which visco-elastic dampers can provide. Application of the method to the design of the building structure with passive damping devices in the bracing system and to the suspension roof with dampers was studied. Through the application of optimal control theory a systematic design procedure to implement dampers in structures is proposed. Copyright ( 2000 John Wiley & Sons, Ltd.

THE γ-FUNCTION PSEUDODYNAMIC ALGORITHM

Abstract: Practical applications of the γ-function dissipative explicit method to pseudodynamic tests are thoroughly investigated herein. Detailed implementation of this pseudodynamic algorithm is schematically sketched. Numerical experiments and verification tests strongly indicate that the γ-function dissipative explicit method can effectively filter out the spurious participation of high frequency responses while the lower mode responses can be obtained very accurately. In addition, error propagation analysis also shows that the γ-function dissipative explicit method possesses much better error propagation characteristics when compared to the Newmark explicit method. Thus, this pseudodynamic algorithm is very suitable for the test system where the responses are dominated by the low frequency modes and the high frequency responses are of no interest.

Empirical model for estimating Fourier amplitude spectra of ground acceleration in Taiwan region

Abstract: SUMMARY A collection of ground-motion recordings (1070 acceleration records) of moderate (5.1)M L )6.5) earthquakes obtained during the execution of the Taiwan Strong Motion Instrumentation Program (TSMIP) since 1991 was used to study source scaling model and attenuation relations for a wide range of earthquake magnitudes and distances and to verify the models developed recently for the Taiwan region. The results of the analysis reveal that the acceleration spectra of the most signi"cant part of the records, starting from S-wave arrival, can be modelled accurately using the Brune’s u-squared source model with magnitudedependent stress parameter *p, that should be determined using the recently proposed regional relationships between magnitude (M L ) and seismic moment (M 0 ) and between M 0 and *p. The anelastic attenuation Q of spectral amplitudes with distance may be described as Q"225 f 1.1 both for deep (depth more than 35 km) and shallow earthquakes. The source scaling and attenuation models allow a satisfactory prediction of the peak ground acceleration for magnitudes 5.1)M)6.5 and distances up to about 200 km in the Taiwan region, and may be useful for seismic hazard assessment. Copyright ( 2000 John Wiley & Sons, Ltd.

On Evaluation of Lamb's Integrals for Waves in a Two-Dimension Elastic Half-Space

Abstract: In this paper, a modified version of the method of steepest descent is proposed for the evaluation of Lamb's integrals which can be considered as basis functions dealing with the development of the transition matrix method which can be used to study the wave scattering in a two-dimensional elastic half-space. The formal solutions of the generalized Lamb's problem are studied and evaluated on the basis of the proposed method. After defining a phase function which presents in wavenumber integral, an exact mapping and an inverse mapping can be obtained according to the phase function. Thus, the original integration path can be deformed into an equivalent admissible path, namely, steepest descent path which passed through the saddle point, and then mapped onto a real axis of mapping plane, finally, resulted in an integral of Hermite type. This integral can be efficiently evaluated numerically in spite of either near- to far-field or low to high frequency. At the same time, the asymptotic value can easily be obtained by applying the proposed method. The numerical results for generalized Lamb's solutions are calculated and compared with analytic, asymptotic or other existing data, the excellent agreements are found. The properties of generalized Lamb's solutions are studied and discussed in details. Their possible applications for wave scattering in elastic half-space are also pointed out.

An accurate solution for the responses of circular curved beams subjected to a moving load

Abstract: In this paper, an accurate and effective solution for a circular curved beam subjected to a moving load is proposed, which incorporates the dynamic stiffness matrix into the Laplace transform technique. In the Laplace domain, the dynamic stiffness matrix and equivalent nodal force vector for a moving load are explicitly formulated based on the general closed-form solution of the differential equations for a circular curved beam subjected to a moving load. A comparison with the modal superposition solution for the case of a simply supported curved beam confirms the high accuracy and applicability of the proposed solution. The internal reactions at any desired location can easily be obtained with high accuracy using the proposed solution, while a large number of elements are usually required for using the finite element method. Furthermore, the jump behaviour of the shear force due to passage of the load is clearly described by the present solution without the Gibb's phenomenon, which cannot be achieved by the modal superposition solution. Finally, the present solution is employed to study the dynamic behaviour of circular curved beams subjected to a moving load considering the effects of the loading characteristics, including the moving speed and excitation frequency, and the effects of the characteristics of curved beams such as the radius of curvature, number of spans, opening angles and damping. The impact factors for displacement and internal reactions are presented. Copyright © 2000 John Wiley & Sons, Ltd.

Damage to hydraulic facilities from the Chi-Chi (Taiwan) earthquake

Abstract: On September 21, 1999, the Chi‐Chi (Taiwan) Earthquake with a local magnitude of 7.3, struck west‐central Taiwan and resulted in tremendous disasters with a death toll over 2,000. Hydraulic facilities such as river banks, levees, dams, weirs, channels, and irrigation systems were seriously damaged in the counties of Miaoli, Taichung, Changhua, Yunlin, and Nantou. In addition, some waterways were blocked by landslide materials, and thus, new lakes were formed. The damage to hydraulic facilities and the causes are thoroughly investigated. The performance of dams under this earthquake is discussed in view of earthquake resistant design. The inundation maps for the downstream lowlands of the blocked creeks are analyzed by using a dam‐break flow numerical model. As a result, the damaged facilities are identified and suggestions for restoration are proposed. The results can be used as a reference in proposing strategies for hazard mitigation and recovery plans.