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This study presents a structural health monitoring method for damage identification and localization of a structure, which incorporated with the principal component analysis (PCA) based data compression and pattern recognition. Through the distribution of sensing node in the structure, an experimental twin-tower steel structure on shaking table test, the dynamic response at different point in the structure is collected. Two different damage scenarios are created in the structure: (1) buckling of the first story bracing member of tower A, (2) buckling of the 2nd floor bracing member of tower A. To extract the features from the vibration measurement, first, stochastic subspace identification and recursive subspace identification methods were applied to extract the modal parameters of their structural system. Then the FRF-based damage assessment using PCA data compression and the scalogram-based novelty detection are used to obtained patterns in some significant respect on damage assessment. Finally, based on the change of flexibility matrix of the system, damage location can be identified..

The effects of earthquake-induced basin amplification are caused by the interaction of wave-fields with a basin boundary, which depend on complex source to site distances, basin geometry (topography), and sediment distribution within the basin. In this study the identification of long-period waves induced by strong earthquake motions through basin topography together with local site effects of the basin is investigated. Through multivariate singular spectrum analysis (MSSA), a unique analysis tool for extracting tendencies and harmonic components in geophysical time series is used to extract the long-period wave of basin response caused by the seismic events. Seismic response data of Taipei Basin were used to examine the existing of the lowest dominant frequency of the basin caused by basin topography. Finally, the seismic-induced ground motion data can be separated to local site effects and the basin motion caused by the effect of topography.

A scour monitoring system with a micro camera tracking the bed-level images is proposed in this study. Two image recognition algorithms have been developed to support the bed-level image tracking approach. Through the laboratory experiments of pier scour, this study demonstrates that the proposed system is able to accurately monitor the scour-depth evolution in real time. In addition, five commonly-used temporal scour models are employed to simulate scour-depth evolution and their results are compared with monitoring data. In general, the results indicate that the proposed scour monitoring system has the potential for further applications in the field.

The objective of this paper is to discuss two different categories on structural damage detection: One is the centralized feature extraction technique by using multi-sensor architecture and the other is the pattern-level data fusion by using the extracted features from individual sensor. The covariance-driven stochastic subspace identification and multivariate singular spectrum analysis are applied for the centralized feature extraction. For pattern-level feature recognition wavelet packet transforms and power spectral density from individual sensing record is used. Through both centralized and pattern-level feature extraction the results can not only detect the occurrence of structural damage but also can locate the damage. Finally, the dynamic finite element model updating is used for damage quantification. Verification of the proposed algorithms by using a research-scale bridge scouring test model to detect the damage occurrence and severity during scouring is presented. Finally, discussion on the computation effectiveness among different method is made.

The local flexibility method (LFM), which can determine local stiffness variations of beam structures using measured modal parameters, is a promising approach for damage detection of structures using vibration signals. The LFM method is founded on virtual forces that cause nonzero stresses within a local part of the structure. In this study, non-local virtual forces which cause concentrated stresses in a local part and nonzero stresses in the other parts of a structure are employed. The theoretical basis of the proposed pseudo local flexibility method (PLFM) which uses the non-local virtual forces is derived. The effects of the number of modes on damage detection results of three damage scenarios of a numerical hyperstatic beam are studied. The results show that much fewer modes are required for the PLFM to estimate the damage locations and extents. Therefore, the feasibility of the PLFM is higher due to limited number of high quality modes can be identified in real world application, especially for ambient vibration measurement.

This study extracted some P-wave features from the first few seconds of vertical ground acceleration of a single station. These features include the predominant period, peak acceleration amplitude, peak velocity amplitude, peak displacement amplitude, cumulative absolute velocity and integral of the squared velocity. The support vector regression was employed to establish a regression model which can predict the peak ground acceleration according to these features. Some representative earthquake records of the Taiwan Strong Motion Instrumentation Program from 1992 to 2006 were used to train and validate the support vector regression model. Then the constructed model was tested using the whole earthquake records of the same period as well as the 2010 Kaohsiung earthquake with 6.4 M L . The effects on the performance of the regression models using different P-wave features and different length of time window to extract these features are studied. The results illustrated that, if the first 3 s of the vertical ground acceleration was used, the standard deviation of the predicted peak ground acceleration error of the whole tested 15-years earthquake records is 20.89 gal.The length of time window could be shortened, e.g. 1 s, and the prediction error is slightly sacrificed, in order to prolong the lead-time before destructive S-waves reaches.

The objective of this paper is to develop an on-line tracking of system parameter estimation and damage detection techniques using response measurements. To avoid the singular-value-decomposition in data Hankel matrix, a new subspace identification algorithm was developed. Seismic response data of a 3-story steel frame with abrupt change of inter-story stiffness from the shaking table test was used to verify the proposed recursive subspace identification (RSI) method by using both input and output measurements. With the implementation of forgetting factor in RSI method the ability of on-line damage detection of the abrupt change of structural stiffness can be enhanced. Then, the recursive stochastic subspace identification (RSSI) algorithm is also developed for continuous structural health monitor of structure by using the output-only measurements. Verification of the proposed RSSI method by using the white noise response data of a 2-story reinforced concrete frame from its low level white noise excitation was used. Discussion of the subspace identification model parameters is also investigated.

A biaxial hysteretic model is developed to take into account the commonly observed hysteretic characteristics of strength and stiffness degradation, pinching and biaxial interaction. The concept of zero force point is proposed to develop the biaxial hysteretic model. Two non-linear inelastic springs and one linear elastic spring are connected in parallel to define the cyclic behavior of the proposed biaxial hysteretic model. The proposed biaxial hysteretic model is rate-independent and capable of simulating not only global (such as story shear force versus story drift response of the whole structure) but also the local hysteretic behavior of structural member (such as moment versus curvature or plastic rotation response of a structural element). The biaxial cyclic loading test data of six reinforced concrete columns, which are designed for flexural failure and shear failure, are used to validate the proposed biaxial hysteretic model.

The mitigation of torsional responses in structures using semi-active devices is pursued in the current study. Multiple magnetorheological (MR) dampers are employed for real-time control of the response of a benchmark structure to earthquake excitations. MR damper resistance levels are intelligently managed by a global fuzzy logic controller (FLC). The FLC is generated using a controlled-elitist genetic algorithm (GA). Development of an optimal FLC is expedited by a discretized search space of fuzzy logic membership functions. To enable robust control an excitation is created for training by a GA using the RSPMatch2005 algorithm that modifies historic ground records in the time-domain by wavelet operations. Both numerical and large-scale experimental efforts are undertaken to validate the proposed control system. Results show that the GA-optimized FLC control provides a favorable balance in reduction of inter-story drift and absolute acceleration levels.

The objective of this paper is to present two modal identification methods that extract dynamic characteristics from output-only data sets collected by a low-cost and rapid-to-deploy wireless structural monitoring system installed upon a long-span cable-stayed bridge. Specifically, an extensive program of full-scale ambient vibration testing has been conducted to measure the dynamic response of the 240 m Gi-Lu cable-stayed bridge located in Nantou County, Taiwan. Two different output-only identification methods are used to analyze the set of ambient vibration data: the stochastic subspace identification method (SSI) and the frequency domain decomposition method (FDD). A total of 10 modal frequencies and their associated mode shapes are identified from the dynamic interaction between the bridge’s cables and deck vibrations within the frequency range of 0–7 Hz. The majority of the modal frequencies observed from recording cable vibrations are also found to be associated with the deck vibrations, implying considerable interaction between the deck and cables.

Validation of fuzzy logic controllers that are optimized by a genetic algorithm is pursued in this study. Fuzzy logic controllers are designed to manage two 20 kN magnetorheological dampers for mitigation of seismic loads applied to a 9 m tall, three-story steel frame benchmark building. In order to develop a set of robust controllers that are sensitive to a variety of excitations, a genetic algorithm that considers multiple objectives concurrently is proposed. Four optimization objectives have been selected which necessitates employment of a controlled elitist genetic algorithm. Optimal controllers are identified and validated through numerical simulation and full-scale experimental shake table tests for a variety of seismic excitations. Furthermore, a modified version of the same genetic algorithm is used to identify a state-space representation of the benchmark structure. Results show that optimized fuzzy logic controllers are robust and effective in reduction of both displacement and acceleration responses for both near- and far-field seismic events.

The frequency-dependent amplification for rock (NEHRP-class B) sites was studied using earthquake ground-motion database collected in Taiwan during implementation of the Taiwan Strong Motion Instrumentation Program. The database used includes several hundred records from earthquakes of M L 4.0–7.3 occurred between 1993 and 2004. The characteristics of amplification were evaluated using the well-known technique of horizontal-to-vertical Fourier spectral ratio (H/V) of the S-wave phase [Lermo J, Chavez-Garcia FJ. Site effect evaluation using spectral ratios with only one station. Bull Seism Soc Am 1993;83:1574–94]. The study allows us to analyze peculiarities of rock sites amplification in Northern and Eastern Taiwan. It was suggested to divide the NEHRP-class B site amplification into four types based on frequency of maximum amplification and the shape of amplification function. The applicability of the technique was also checked for a few stiff and soft soil sites (NEHRP-classes D and E).

Full-scale experiments are carried out on a single-degree-of-freedom mass that is equipped with a hybrid base isolation system. The isolator consists of a set of four friction pendulum system (FPS) bearings and a magnetorheological (MR) damper. The 13,620 kg mass and its hybrid isolation system are subjected to various intensities of near- and far-fault earthquakes on a large shake table. The proposed fuzzy controller uses feedback from displacement or acceleration transducers attached to the structure to modulate resistance of the semi-active damper to motion. Results from several types of passive and semi-active control strategies are summarized and compared. The study shows that a combination of FPS bearings and an adjustable MR damper can provide robust control of vibration for a large full-scale structure undergoing a wide variety of seismic loads. Low power consumption, real-time feedback control, and fail-safe operation are validated in this study. A combination of the FPS bearings and the MR damper appears to offer significant possibilities for reduction of displacement and acceleration due to seismic load. A neuro-fuzzy model is used to represent behavior of the damper for various displacement, velocity, and voltage combinations that are obtained from a series of laboratory evaluation tests. Modeling of the FPS bearings is carried out with a nonlinear analytical equation and neuro-fuzzy training. Numerical simulation using neuro-fuzzy models of the MR damper and FPS bearings predict the response of the hybrid base isolation system very well. Results show that dynamic behavior of the FPS bearings and MR damper can be successfully estimated using these neuro-fuzzy models.

The dynamic response of seismic isolated continuous girder bridges subjected to either near-fault or far-field ground motions is compared to the non-isolated ones. Near-fault earthquake ground motion data are collected from the 1999 Taiwan Chi-Chi earthquake. The earthquake data recorded at the same sites from other events serve as far-field ground motions. Typical three-span continuous concrete box girder bridges designed under Taiwan seismic design specifications of highway bridges are adopted for this study. These bridges are assumed straight, founded on rigid rock and only the longitudinal response is considered. Parametric studies for the dynamic responses of isolated bridges by input near-fault ground motions are developed. The PGV/PGA value of near-fault earthquake records is identified as the key parameter governing the bridge response.

The objective of this paper is to identify the first mode ground period Tg, at each interesting site along Taiwan High Speed Rail (THSR) route, and further, to determine the site-dependent design response spectrum for particular sites with Tg larger than 1 s. In this paper, a linear model of shear wave propagating in a multi-layered half-space is developed to identify the first mode ground period Tg of an interesting site on the basis of the field bore hole data. Furthermore, for each one of the strong ground motion observation stations within the Chiayi-Tainan area, the first mode ground period Tg was identified by either coda waves or pre-event ambient vibrations from the seismograms. In addition, the site-specific parameter Cv in defining the normalized response spectrum was also determined based on the observed strong ground motions at the specified observation station, and hence the empirical function between Tg and Cv can be regressed for this interesting area. Therefore, for a particular site along THSR route within the Chiayi-Tainan area, the site-specific parameter Cv can be determined from the regressed empirical function by the identified first mode ground period Tg, and further, used to develop the site-dependent design response spectrum.

Design seismic forces depend on the peak ground acceleration (PGA) and on the shape of design spectrum curves dictated in building codes. At present there is no doubt that it is necessary to construct so-called “site and region-specific” design input ground motions reflecting influence from different magnitude events at different distances that may occur during a specified time period. A unified approach to ground motion parameters estimation is described. A collection of ground motion recordings of small to moderate (3.0–3.5≤ML≤6.5) earthquakes obtained during the execution of the Taiwan Strong Motion Instrumentation Program (TSMIP) since 1991 was used to study source scaling model, attenuation relations and site effects in Taiwan region. A stochastic simulation technique was applied to predict PGA and response spectra for the Taipei basin. “Site and region-dependent” uniform hazard response spectra were estimated for various geological conditions in the Taipei basin using a technique of probabilistic seismic hazard analysis.

The goal of this study is to provide a better understanding on the behavior of pinching and softening effects for bridge column under earthquake loading. In the first part, a nonlinear cyclic loading test on a well-designed ductile RC bridge column was carried out experimentally. The hysteretic behavior of the bridge column was generated. In the second part, finite element analyses were used to predict the response under earthquake excitation. The hysteretic behavior obtained by experiment will be used as an input in material modeling for finite element programs. Discussions were made by using different computer codes to simulate the effects of pinching and softening of bridge column subjected to earthquake loading. Due to the inadequate functions of the element modeling, the theoretical system may underestimate the structural response under strong earthquake loading particularly on the prediction of softening and pinching effects.

The Park and Ang damage model was used as the "Structural Damage Control Model" to study the seismic design parameters. This damage control model included the displacement ductility and hysteretic energy in the analysis of elastic-perfect-plastic single-degree-of-freedom system. Based on this damage control model, the reduction factor and yield base shear coefficient are discussed. Seismic data collected from Taipei basin were used to examine the code-provided yield base shear coefficient which reflects the influence of using a damage control model in the seismic design parameter. Effects of seismic source as well as Taipei basin topography are also considered in examining the variation of yield base shear coefficient.

Statistical analysis of the response spectra due to both horizontal and vertical ground excitations is conducted. A method is presented for generating a uniform hazard response spectrum making use of the seismic hazard curve expressing annual probability of exceedance as a function of peak ground acceleration (PGA), a set of normalized mean response spectra, and a coefficient-of-variation function for the random normalized spectral values in terms of period T . The response spectra of the system are calculated by considering both horizontal and vertical excitations simultaneously. Comparison on the uniform hazard response spectrum for case of single input (horizontal excitation only) and for case of multiple inputs (horizontal and vertical excitations) are made. It is important to note that the effect of load ratio ( Mg / P cr ) as well as the PGA ratio between horizontal and vertical ground accelerations are two important parameters in the analysis of structural systems subjected to both horizontal and vertical ground motions.

This purpose of this paper is to study the dynamic characteristics of the Fei-Tsui arch dam using the seismic response data and the ambient vibration data. For the identification of dam properties from seismic response data, the multiple inputs from the abutment of the dam to represent the nonuniform excitations of seismic input motion are considered, and the ARX model is applied using the discrete-time linear filtering approach with least-squares approximation to identify the dynamic characteristics of the dam. The system modal dampings, natural frequencies and frequency response functions are identified. A comparison of the identified modal parameters is made among different seismic events. Post-earthquake safety evaluation of the dam can be made based on the identified model. Finally, the ambient vibration test of the dam is performed to identify the mode shapes along the dam crest.

This paper aims to study the effectiveness of using an active variable damper system to control seismically excited building structures. The Liapunov direct method was used to design the controller and the weighting matrix Q can be obtained by making the derivative of the Liapunov function as negative as possible. The control system, using an active variable damper, provides time-varying damping to the structure at every instant of time and the error estimate of system matrix A will not significantly effect the control result. A comparison of the efficiency of the control between classical optimal control and the present method is made. A combination of the active variable damper system with a passive base-isolation system proved to be the most effective form of control of the building response when subjected to seismic excitation even under different site conditions

A response spectrum method is proposed for the seismic analysis of a multisupport structure subjected to spatially varying ground motion. Based on theoretical results by Der Kiureghian and Hofer, an approximate and efficient analysis of the frequency integral of the cross-correlation function of multisupport excitation is presented. A two-span beam-like structure is studied to demonstrate the application of this proposed method and to characterize the influence of the differential support motion. Treatment of the various combinations of phase relationships between supports is also discussed.

This paper presents a procedure to perform the risk analysis for ground failure by liquefaction. The first part of this study describes the differential equation of a smooth hysteretic model to characterize the behavior of the soil under random loading. The parameters of the proposed model to represent the experimental relationship are discussed. The second part of this study is to develop a method to calculate the probability that a specified volume of soil will liquefy at a given depth in the deposit. The liquefaction is defined as the result of cumulative damage caused by seismic loading. The fatigue life of soil can be determined on the basis of the NS relationship and Miner's cumulative damage law. The rain-flow method is used to count the number of cycles of stress response of the soil deposit. Finally, the probability of liquefaction is obtained by integration over all the possible ground motion and the fragility curves of liquefaction potential. The sensitivity of the reliability against liquefaction to soil system parameters is also examined.

The possibility of enhancing Tuned Mass Damper (TMP) effectiveness with an added active control capability is presented in this paper. The weighting matrix associated with the components of the state vector are discussed. Through random vibration analysis, the relationship between response variance and the elements of the weighting matrix are examined from which the arrangement of the weighting matrix associated with the components of the state vector is determined. Except for the ideal case of a control system, time delay compensation of the control force in instantaneous optimal control is seriously considered. In this paper, a predictive control law has been developed in which emphasis is placed on compensation for the time delay due to the control action. The control efficiency is investigated in detail. Numerical examples are worked out to demonstrate the control efficiency of the proposed algorithm to the vibration of a bridge-like flexible structure.

The purpose of this paper is to study the dynamic characteristics of soil deposits during earthquake excitation. Generally, soil deposits are known to exhibit significant nonlinear behavior under strong earthquake excitations. Observation of soil earthquake response from ground surface and downhole data provides the information on the differences between strong motion and weak motion, and the effect of soil nonlinearity during strong earthquakes is also examined. Based on the evolutionary power spectral analysis, simplified wave type separation can be done. The soil amplification due to body waves is quite significant in the present study of three earthquake events. A systematic identification method is proposed to identify the hysteresis behavior of soil deposits. The extended Kalman filtering technique is applied to identify the bilinear model parameters of soil restoring forces during strong shaking.

The scope of this study is to evaluate, using three nonlinear, single-degree-of-freedom models (representing both nondeteriorating and deteriorating systems), the inelastic response characteristics which permit the assessment of fatigue damage due to seismic excitation. The systems, with a period of 1 s, are subjected to 69 recorded ground motions of different magnitudes, durations and hypocentral distances. The response parameters are the ductility index (defined as the maximum response normalized to yield displacement) and the energy index (defined as the cumulative hysteretic energy). Based on the rain-flow cycle counting method, the relationships between the response parameters and the cumulative damage are established. Emprical prediction models for cumulative damage are also developed.

The objectives of this paper are (1) to obtain estimates on the effect of uncertainties of the hazard model, and (2) to evaluate the seismic hazard in Taiwan for structural analysis and design purposes. The seismic hazard in the Taiwan area is presented in terms of an iso-acceleration map. Such a map is developed for return periods of peak ground acceleration of 225 years and 475 years. The contour map of b- values and mean occurence rates for this region is also presented. Uncertainty analyses of model parameters in hazard analysis are concentrated on the analysis of dispersion of PGA values and the probabilistic modeling of stationary and nonstationary Poisson models of occurrences. Th e overall results are considered to be conservative since for most uncertainty analyses the more conservative values are used.

A method for conducting a seismic hazard analysis of active faults using a fault-rupture model and a point-source model is presented. Based on a peak ground acceleration (PGA) attenuation formula, the annual probability of exceedance at a specific site is calculated. The uniform hazard spectrum is also determined based on a spectral amplitude attenuation formula. To improve the reliability of the seismic hazard analysis, a detailed study of hazard parameters is conducted and discussed. A specific site in Taiwan is chosen to illustrate the hazard analysis.

The coherence of strong ground motions over short distances has important implications for waveform modelling. In this paper we present some computational results demonstrating the existence of spatial variation of seismic waves. The Smart -1 array recordings are used in this study as examples. The measured coherency suggests that the frequency-dependent exponential form of the spatial correlation function could represent the behavior of wave coherency. The scattered wave field caused by the irregular boundary can also be observed through the spectral analysis. A method of analyzing the spatially varied earthquake ground motion for the purpose of the design and analysis of underground lifeline system is also discussed.

The purpose of this paper is to study the directionality in spatial variation of seismic waves. Characteristics of mutual correlations of seismic ground motion of different points for different components of frequencies were analysed through the definition of normalized covariance. Two variables were involved in the study of directionality, the incident angle of wave propagation projected into the horizontal ground plane and the relative angle. A mathematical model is presented to include the directionality in spatial variation of seismic waves. From the analysis of frequency-wave number spectra, the simulation of spatially two-dimensional stochastic waves can be modelled using a deterministic model for the low frequency range of seismograms. Both directionality and simulation in spatial variation of seismic waves were studied based on the data recorded by the SMART-1 array.

The purpose of this paper is to study the aseismic displacement of multi-supported bridge to multiple seismic excitations. The first part deals with the systematic way of simulation of spatial variation of seismic waves. The evolutionary spectrum model was adopted, and the model parameters were estimated based on the data recorded by SMART-1 array. The local soil effect was also adopted in this simulation model. The second part deals with the stochastic earthquake analysis of multi-supported structures. The stochastic earthquake response of simply-supported girder bridge subjected to spatial variation of seismic wave was studied as an example. The relative displacement between the top of two piers was carefully examined as a function of model parameters as well as the local soil condition. It is found that the variation of structural properties between two adjacent structures have significant effects on the aseismic displacement between two supports. The local soil conditions, such as the depth of soil deposit, wave coherence, may also have an important effect on this aseismic displacement of multi-supported bridge.

The purpose of this paper is to estimate the possible effects of the source as well as the local soil characteristics on the spectral characteristics of ground motions. A stochastic soil amplification function was first developed. The parameters that control the spectral shape of ground motion were depth of soil deposit, soil density and shear modulus, corner frequency of the source as well as the high frequency decay rate of acceleration. The result of the model was compared to the data record by SMART-1 array. The development of seismic design spectrum was also discussed based on the proposed ground motion model. It is concluded that the local soil density, depth of soil deposit and the source corner frequency are the most significant factors to the influence of design spectrum. With the proposed ground motion model, a method to predict the design spectrum for a given earthquake magnitude can be constructed.

The extended Kalman filter is applied to a system identification problem of seismic structural systems. This paper presents an identification method for an equivalent linear system, a bilinear hysteric restoring system and a bilinear hysteretic restoring system with stiffness degradation effect. For the accuracy of this present proposal, the justification of the method is investigated on numerically simulated data on response of a known system as well as a known degrading system. The proposed method is formulated in detail. It is then applied to identify the hysteresis behaviour of two buildings which were subjected to earthquake loads.