Search

A direct eigenvalue analysis approach for solving the stability problem of periodically supported beams with multi-mode coupling vibration under general harmonic excitations is developed based on the Floquet theorem, Fourier series and matrix eigenvalue analysis. The transverse periodic supports are considered for improving the parametrically excited stability of beams under longitudinal periodic excitations. The dynamic stability of parametrically excited vibration of the beam with transverse spaced supports under longitudinal harmonic excitations is studied. The partial differential equation of motion of the beam with spaced supports under harmonic excitations is given and converted into ordinary differential equations with time-varying periodic parameters using the Galerkin method, which describe the parametrically excited vibration of the beam with coupled multiple modes. The fundamental solution to the equations is expressed as the product of periodic and exponential components based on the Floquet theorem. The periodic component and periodic parameters are expanded into Fourier series, and the matrix eigenvalue equation is obtained which is used for directly determining the parametrically excited stability. The dynamic stability of parametrically excited vibration of the beam with spaced supports under harmonic excitations is illustrated by numerical results on unstable regions. The influence of the periodic supports and excitation parameters on the parametrically excited stability is explored. The parametrically excited stability of the beam with multi-mode coupling vibration can be improved by the periodic supports. The developed analysis method is applicable to more general period-parametric beams with multi-mode coupling vibration under various harmonic excitations. [ABSTRACT FROM AUTHOR]

This paper demonstrates that a sandwich beam with the continuous harmonic distribution of geometrical and physical parameters can be adjusted to yield the desired response. The facial layer thickness and core layer modulus of the sandwich beam are considered as the harmonic distribution. The frequency responses and response spectral densities of the finite harmonic sandwich beam with supported mass under stochastic support motion excitations are studied for improving the performance. The partial differential equations for the horizontal and vertical coupling motions of the harmonic sandwich beam are derived and converted into the ordinary differential equations for the multi-mode coupling vibration. The modal stiffness, mass and excitation coefficients are functions of the harmonic distribution parameters (HDPs). The vibration responses including resonances and anti-resonances can be adjusted by the harmonic parameter wave numbers and amplitudes. The frequency responses and response spectral densities of the harmonic sandwich beam are obtained. The single and two-mode vibrations are analyzed to demonstrate that the response resonance and anti-resonance can be adjusted via the HDPs of the beam. The substantially improved vibration response characteristics and the influence of the HDPs on the response spectral densities are illustrated with numerical results. [ABSTRACT FROM AUTHOR]

An adaptive solution to semiactive control of cable vibration is formulated by extending the linear quadratic Gaussian (LQG) control from time domain to frequency domain. Frequency shaping is introduced via the frequency dependent weights in the cost function to address the control effectiveness and robustness. The Hilbert-Huang transform (HHT) technique is further synthesized for online tuning of the controller gain adaptively to track the cable vibration evolution, which also obviates the iterative optimal gain selection for the trade-off between control performance and energy in the conventional time domain LQG (T-LQG) control. The developed adaptive frequency-shaped LQG (AF-LQG) control is realized by collocated self-sensing magnetorheological (MR) dampers considering the nonlinear damper dynamics for force tracking control. Performance of the AF-LQG control is numerically validated on a bridge cable transversely attached with a self-sensing MR damper. The results demonstrate the adaptivity in gain tuning of the AF-LQG control to target for the dominant cable mode for vibration energy dissipation, as well as its enhanced control efficacy over the optimal passive MR damping control and the T-LQG control for different excitation modes and damper locations. [ABSTRACT FROM AUTHOR]

Lifecycle structural health monitoring (SHM) systems provide an abundance of information that is greatly beneficial for securing structural safety over the whole service life. In application to large-scale structures, the management of accumulated massive data from a sophisticated long-term SHM system poses a challenge. A robust data management system (DMS), which not only facilitates spatiotemporal data management but also enables display in an attractive way, is highly desirable. This article presents the development of an effective visualized DMS specific for managing immense and heterogeneous SHM data by integrating nested relational database, three-dimensional (3D) model, and virtual reality (VR) technology and demonstrates its application to an instrumented supertall structure. A custom nested data model is designed to store redundant inherent temporal data and hierarchical inherent spatial data. Strategies for speeding up querying massive data are set up in the database. Making use of OpenSceneGraph (OSG) 3D engine, a 3D model is reconstructed from the 3D spatial data, which serves as a platform for data visualization. A four-dimensional (4D) animation protocol is presented by tying temporal data and construction schedule to the 3D model. The efficiency of the proposed DMS is exemplified through its application to a supertall structure instrumented with a sophisticated long-term SHMsystem. [ABSTRACT FROM AUTHOR]

Background: Obesity has become a major health problem in contemporary society and it is closely related to many chronic diseases, so it is an important issue for measuring adiposity accurately and predicting its future. Prevention and treatment of overweight and obesity has become one of the key prevention and treatment of metabolic disorders. Objective: In this study, we compared the ability of the four anthropometric indicators (body mass index, waist circumstance, waist--height ratio, waist-to-hip ratio) to identify metabolic disorders (hypertension, hyperlipidaemia, hyperglycemia and hyperuricemia) by receiver operating characteristic (ROC) curve analyses and to provide evidence for clinical practice. Methods: In this large scale cross-sectional study, 13,275 Han adults (including 7595 males and 5680 females) received physical examination between January, 2009 and January, 2010 in Xuanwu Hospital of Capital Medical University were investigated by the means of questionnaire, Meanwhile, the physical examination and serological results were recorded. A package known as Statistical Package for Social Scientist (SPSS) was employed to analyse the responses while t-test, one-way analysis of variance (ANOVA), ROC analysis and chi-square statistical methods were used to test the hypotheses. Results: WC, WHtR, WHR and BMI were all significantly (P < 0.001) correlated with all metabolic risk factors regardless of gender. And the area under the curve (AUC) of WHtR was significantly greater than that of WC, BMI or WHR in the prediction of hypertension, hyperlipidaemia, hyperglycemia and hyperuricemia. [ABSTRACT FROM AUTHOR]

The parametrically excited instability of the spatially periodic visco-elastomer sandwich plate with supported masses under quadrilateral longitudinal temporal harmonic excitations is studied. The improvability of the parametrically excited instability by periodic distribution parameters is explored. The direct eigenvalue analysis approach for solving the parametrically excited stability problem of the periodic sandwich plate system under longitudinal harmonic excitations is proposed. The spatial periodic distribution of facial layer thickness and core layer modulus of the sandwich plate is considered. The non-linear partial differential equations of longitudinal and transverse coupling motions of the periodic visco-elastomer sandwich plate with supported masses under biaxial longitudinal boundary excitations are derived. The longitudinal displacements of the sandwich plate are separated into two parts and the longitudinal boundary excitations relevant to symmetric part are incorporated into the sandwich plate system. Then the partial differential equations with boundary excitations are converted into parametrically excited system equations and further converted into ordinary differential equations with time-varying parameters, which describe the parametrically excited vibration with multi-mode coupling of the periodic sandwich plate system. The fundamental perturbation solution to the equations is expressed as the product of periodic and exponential parts based on the Floquet theorem. The ordinary differential equations with harmonic parameters are converted into a set of algebraic equations using the harmonic balance method. Then the parametrically excited instability of the periodic sandwich plate system is determined directly by matrix eigenvalues. The overall instability characteristics of parametrically excited vibration with multi-mode coupling of the system under longitudinal harmonic excitations are illustrated by numerical results on unstable regions. The parametrically excited instability can be improved by the spatially periodic distribution of geometrical and physical parameters. The proposed approach is applicable to general sandwich structures with spatial distribution parameters in multi-mode-coupling parametrically excited vibrations for overall instability analysis on continuous frequency band. [ABSTRACT FROM AUTHOR]

This paper presents the development and application of a soft-computing technique in identification of forward and inverse dynamics of a self-sensing magnetorheological (MR) damper based on experimental measurements. This technique is developed by the synthesis of an NARX (nonlinear autoregressive with exogenous inputs) model structure and neural network within a Bayesian inference framework. The Bayesian inference procedures essentially eschew overfitting that could occur in network learning and improve generalization (prediction) capability by regularizing the complexity of learning. In applying the developed technique to the self-sensing MR damper, the present and past information of its input and output quantities, which contain the physical knowledge of the damper, is used to formulate its nonlinear dynamics. The NARX network architecture is then optimized to enhance modeling effectiveness, efficiency, and robustness. Experimental data of the damper subjected to both harmonic and random excitations are used for model identification and assessment. Assessment results show that the formulated Bayesian NARX network accurately emulates the nonlinear forward dynamics of the selfsensing MR damper. Improved generalization (prediction) capability of the NARX network model by the Bayesian regulation is observed by comparing the modeling results with and without considering regularization. An inverse dynamic model for the self-sensing MR damper is further formulated by the developed technique. The proposed soft-computing technique is viable to formulate dynamic models of the self-sensing MR damper for structural control applications. [ABSTRACT FROM AUTHOR]

This paper presents an investigation on using the probabilistic neural network (PNN) for damage localization in the suspension Tsing Ma Bridge (TMB) and the cable-stayed Ting Kau Bridge (TKB) from simulated noisy modal data. Because the PNN approach describes measurement data in a Bayesian probabilistic framework, it is promising for structural damage detection in noisy conditions. For locating damage on the TMB deck, the main span of the TMB is divided into a number of segments, and damage to the deck members in a segment is classified as one pattern class. The characteristic ensembles (training samples) for each pattern class are obtained by computing the modal frequency change ratios from a 3D finite element model (FEM) when incurring damage at different members of the same segment and then corrupting the analytical results with random noise. The testing samples for damage localization are obtained in a similar way except that damage is generated at locations different from the training samples. For damage region/type identification of the TKB, a series of pattern classes are defined to depict different scenarios with damage occurring at different portions/components. Research efforts have been focused on evaluating the influence of measurement noise level on the identification accuracy. [ABSTRACT FROM AUTHOR]

In comparison with above-ground structures, the investigation of underground space structures still faces great challenges because of the extremely complicated constitutive relationships of the soils or rocks. Implementation of structural health monitoring (SHM) systems on the underground structures such as tunnels commencing from the construction stage may be of help in understanding their operational behaviors and long-term trends. This paper explores the application of the fiber Bragg grating (FBG) sensing technology for safety monitoring during railway tunnel construction. An FBG-based temperature monitoring system is first developed for real-time temperature measurement of the frozen soils during freezing construction of a metro-tunnel cross-passage. Through in-situ deployment of FBG-based liquid-level sensors, the subgrade settlement of a segment of a high-speed rail line is then monitored in an automatic manner during construction of an undercrossing tunnel. The field results indicate that the FBG sensors are robust and reliable in perceiving temperature and strain variations even in harsh environments. [ABSTRACT FROM AUTHOR]

Vibration measurement is one of the most widely used methods for tension evaluation and condition assessment of stay cables in cable-stayed bridges. In the existing practice, the tension force of a cable is identified from the measured modal frequencies with the use of the taut string theory or empirical formulae, by assuming pre-determined structural parameters (geometric and material parameters) and boundary conditions of the cable. As a result, an inaccurate estimation of the cable tension may be obtained when there is an error in the pre-determined structural parameters and boundary conditions. Moreover, the commonly used empirical formulae are not applicable in the case when the cable is intermediately attached with dampers. In the present study, a method enabling simultaneous identification of cable tension and other structural parameters from the measured modal frequencies is developed. A precise finite element model (FEM) accounting for cable flexural rigidity, sag-extensibility, spatial variability of dynamic tension, boundary conditions, lumped masses and intermediate supports and/or dampers is first formulated as the reference model in parameter identification so that the modeling error is minimized. Then the measured multiple modal frequencies are used together with the FEM to figure out a nonlinear least-square optimization scheme which helps eliminate measurement error and allows for simultaneous identification of the cable tension and other structural parameters. Application of the proposed method to the Dongting Lake Bridge cables from in-situ ambient vibration measurements illustrates high identification accuracy and fidelity of the proposed method. [ABSTRACT FROM AUTHOR]

This study focuses on how to exploit long-term monitoring data of structural strain for analytical modeling of multimodal rainflow-counted stress spectra by use of the method of finite mixture distributions in conjunction with a hybrid mixture parameter estimation algorithm. The long-term strain data acquired from an instrumented bridge carrying both highway and railway traffic is used to verify the procedure. A wavelet-based filtering technique is first applied to eliminate the temperature effect inherent in the measured strain data. The stress spectrum is obtained by extracting the stress range and mean stress from the stress time histories with the aid of a rainflow counting algorithm. By synthesizing the features captured from daily stress spectra, a representative sample of stress spectrum accounting for multiple loading effects is derived. Then, the modeling of the multimodal stress range is performed by use of finite mixed normal, lognormal, and Weibull distributions, with the best mixed distribution being determined by the Akaike's information criterion (AIC). The joint probability density function (PDF) of the stress range and the mean stress is also estimated by means of a mixture of multivariate distributions. It turns out that the obtained PDFs favorably fit the measurement data and reflect the multimodal property fairly well. The analytical expressions of PDFs resulting from this study would greatly facilitate the monitoring-based fatigue reliability assessment of steel bridges instrumented with structural health monitoring (SHM) system. [ABSTRACT FROM AUTHOR]

The New Headquarters of Shenzhen Stock Exchange (NHSSE), currently being constructed in Shenzhen, China, is a high-rise building with a height of 245 m. One salient feature of NHSSE is its huge floating platform with an overall plan dimension of 98m× 162m and a total height of 24 m, making it one of the largest cantilever structures in the world. In recognition of the uniqueness of the floating platform, a long-term structural health monitoring (SHM) system has been designed and implemented by The Hong Kong Polytechnic University for both in-construction and in-service monitoring of NHSSE. As part of this monitoring system, 224 vibrating-wire strain gauges have been permanently installed to measure the strain responses of key structural components of the floating platform. A wireless strain monitoring system by integrating local tethered data acquisition and long-range wireless data transmission has been developed for real-time strain monitoring and visualization. This paper presents the stress evolution of the floating platform during dismantlement of temporary supports on the basis of the real-time monitoring data and the statistical stress analysis and safety evaluation of the floating platform by use of the long-term monitoring data, as well as the effect of the welding residual stress on structural safety of NHSSE. [ABSTRACT FROM AUTHOR]

Finite-element (FE) model updating aims at the parametric identification of a structure by correcting model parameters in an initial FE model of the structure to reconcile FE predictions with experimental counterparts. However, experimental data inevitably contain a certain level of measurement noise, and the measurement noise will further generate error and uncertainty in updating results. This paper presents a Monte Carlo (MC) simulation study of the effect of measurement noise on updating parameters in FE models updating with regularization, attempting to quantify the distribution functions of updating parameters in face of measurement noise, and evaluating the adequacy of moment-based stochastic FE model updating algorithms. Taking a numerical study of model updating of a simple truss bridge as an example, a series of artificial measurement noise generated with the normal distribution of zero mean and varying variance is introduced into the simulated modal parameters to quantify the effect of measurement noise on updating parameters. The results indicate that the coefficients of variation of the updating parameters are quite different in magnitude, implying different sensitivities of the updating parameters to measurement noise in modal data. In the case of a low level of measurement noise, the updating parameters also comply with normal distributions; in the case of a high measurement noise level, however, the updating parameters are largely nonnormal. The significant deviation from the normal distribution warrants that the low-order, moment-based stochastic FE model updating algorithms may be inadequate in the presence of severe measurement noise. [ABSTRACT FROM AUTHOR]

False-positive or false-negative damage may be signaled by vibration-based structural damage detection methods when the environmental effects on the changes of dynamic characteristics of a structure are not accounted for appropriately. In this paper, a parametric approach for eliminating the temperature effect in vibration-based structural damage detection is proposed that is applicable to structures where dynamic properties and temperature are measured. First, a correlation model between damage-sensitive modal features and temperature is formulated with the back-propagation neural network (BPNN) technique. With the correlation model, the modal features measured under different temperature conditions are normalized to an identical reference status of temperature to eliminate the temperature effect. The normalized modal features are then applied for structural damage identification. The proposed approach is examined in the instrumented Ting Kau Bridge in Hong Kong. Using the long-term monitoring data of both modal frequencies and temperatures, a BPNN correlation model with validated generalization capability is formulated, and the normalized modal frequencies before and after damage are derived and applied for the structural damage alarm using the autoassociative neural network (AANN)-based novelty detection technique. The proposed approach is competent for eliminating the temperature effect and eschewing the false-positive damage alarm that originally occurred when using the measured modal frequencies directly. Case studies assuming damage at different structural components of the bridge are carried out to verify the proposed approach and the detectability of damage using the AANN-based novelty detection technique. The results show that the approach can detect damage when the damage-induced frequency change is as small as 1%. Nevertheless, it is worth mentioning that the frequency-based approach is most effective for detecting damage of a certain severity rather than detecting the onset of damage. [ABSTRACT FROM AUTHOR]

Massive infrastructure projects developed in Hong Kong make for big challenges and unique opportunities for engineers and researchers. The construction of the cables-stayed Stonecutters Bridge sets up a new landmark in the bridge engineering community, with its main span exceeding 1,000 m as well as its sophisticated instrumentation system comprising more than 1,500 sensors. The development of structural health monitoring (SHM) technology has evolved for over 10 years in Hong Kong since the implementation of the so-called 'Wind And Structural Health Monitoring System (WASHMS)' on the suspension Tsing Ma Bridge in 1997. The successful engineering paradigms of implementing and operating SHM systems for five cable-supported bridges and experiences gained by practice and research in the past decade have promoted the applications of this technology beyond Hong Kong and extending from long-span bridges to high-rise structures. In this paper, the evolution in the design methodology for SHM systems, the advancement in several aspects of SHM technology, and a performance comparison between the early implemented and lately developed SHM systems for large-scale bridges are first outlined. Subsequently, the concept of the so-called 'life-cycle structural health monitoring (LSHM)' is addressed by exploring the integration of in-construction monitoring and in-service monitoring and by realizing such an integrated system to a super-tall tower structure. The issue on how an SHM system benefits structural vibration control is also discussed. [ABSTRACT FROM AUTHOR]

A fatigue reliability model which integrates the probability distribution of hot spot stress range with a continuous probabilistic formulation of Miner's damage cumulative rule is developed for fatigue life and reliability evaluation of steel bridges with long-term monitoring data. By considering both the nominal stress obtained by measurements and the corresponding stress concentration factor (SCF) as random variables, a probabilistic model of the hot spot stress is formulated with the use of the S-N curve and the Miner's rule, which is then used to evaluate the fatigue life and failure probability with the aid of structural reliability theory. The proposed method is illustrated using the long-term strain monitoring data from the instrumented Tsing Ma Bridge. A standard daily stress spectrum accounting for highway traffic, railway traffic, and typhoon effects is derived by use of the monitoring data. Then global and local finite element models (FEMs) of the bridge are developed for numerically calculating the SCFs at fatigue-susceptible locations, while the stochastic characteristics of SCF for a typical welded T-joint are obtained by full-scale model experiments of a railway beam section of the bridge. A multimodal probability density function (PDF) of the stress range is derived from the monitoring data using the finite mixed Weibull distributions in conjunction with a hybrid parameter estimation algorithm. The failure probability and reliability index versus fatigue life are achieved from the obtained joint PDF of the hot spot stress in terms of the nominal stress and SCF random variables. [ABSTRACT FROM AUTHOR]

Magneto-rheological elastomers (MREs) are used to construct composite structures for micro-vibration control of equipment under stochastic support-motion excitations. The dynamic behavior of MREs as a smart viscoelastic material is characterized by a complex modulus dependent on vibration frequency and controllable by external magnetic fields. Frequency-domain solution methods for stochastic micro-vibration response analysis of the MRE-based structural systems are developed to derive the system frequency-response function matrices and the expressions of the velocity response spectrum. With these equations, the root-mean-square (RMS) velocity responses in terms of the one-third octave frequency band spectrum can be calculated. Further, the optimization problem of the complex moduli of the MRE cores is defined by minimizing the velocity response spectra and the RMS velocity responses through altering the applied magnetic fields. Simulation results illustrate the influences of MRE parameters on the RMS velocity responses and the high response reduction capacities of the MRE-based structures. In addition, the developed frequency-domain analysis methods are applicable to sandwich beam structures with arbitrary cores characterized by complex shear moduli under stochastic excitations described by power spectral density functions, and are valid for a wide frequency range. [ABSTRACT FROM AUTHOR]

In Hong Kong, a sophisticated long-term structural health monitoring system has been devised by the Highways Department of HKSAR Government to monitor the structural performance and health conditions of three cable-supported bridges. On-structure instrumentation systems for two new long-span bridges are also being implemented. The implementation of these monitoring systems highlights the necessity for developing a monitoring-based structural health evaluation paradigm for long-span bridges. This paper describes the research directed towards this that has been conducted in the Hong Kong Polytechnic University. Taking the instrumented cable-stayed Ting Kau Bridge as a paradigm, the research covers the development of an index system and a database system for monitoring data management, the modelling of the environmental variability of measured modal properties with the intention of eliminating environmental effects in vibration-based damage detection, and the feasibility of using measured modal properties from the deployed vibration sensors for structural damage identification. [ABSTRACT FROM AUTHOR]

The parametric approach to eliminating the temperature-caused modal variability in vibration-based structural damage detection requires a correlation model between the modal properties and environmental temperatures. This paper examines the generalization capability of neural network models, established using long-term monitoring data, for correlation between the modal frequencies and environmental temperatures. A total of 770 h modal frequency and temperature data obtained from an instrumented bridge are available for this study, which are further divided into three sets: training data, validation data, and testing data. A two-layer back-propagation neural network (BPNN) is first trained using the training data by the conventional training algorithm, in which the number of hidden nodes is optimally determined using the validation data. Then two new BPNNs are configured with the same data by applying the early stopping technique and the Bayesian regularization technique, respectively. The reproduction and prediction capabilities of the two new BPNNs are examined in respect of the training data and the unseen testing data, and compared with the performance of the baseline BPNN model. This study indicates that both the early stopping and Bayesian regularization techniques can significantly ameliorate the generalization capability of BPNN-based correlation models, and the BPNN model formulated using the early stopping technique outperforms that using the Bayesian regularization technique in both reproduction and prediction capabilities. [ABSTRACT FROM AUTHOR]

A new static-based method for damage detection of cable-stayed bridges using the changes in cable forces is presented in this paper. In recognizing the fact that damage incurring in bridge girders will cause a redistribution of forces in stay cables, the proposed method uses the measured changes in cable forces to detect the damage in bridge girders. In this method, the damage identification is formulated as an optimization problem in which the cable force error between measurement results and analytical model predictions is minimized. The sensitivities of cable forces with respect to the structural parameters of bridge girders for the linear and geometrically nonlinear bridge structures are obtained by using the direct differentiation method and the finite difference method, respectively, and are used to solve the optimization problem. Regularization technique is used to alleviate ill-conditioning in the solution course of the optimization problem. The validity of the method is illustrated by numerical studies of damage detection of the cable-stayed Sutong Bridge with a main span of 1,088 m. The effect of measurement noises and the number of measured cable forces on the accuracy of damage quantification is investigated. The proposed method correctly identifies the damage locations and damage magnitudes in bridge girders when using noise-free cable forces. It is also shown that structural damage can be quantified with acceptable accuracy in the case of low-level measurement noises and the damaged members being well spaced, and the identification accuracy is greatly improved when the forces in the cables connected to the damaged members are available for damage quantification. [ABSTRACT FROM AUTHOR]

A symplectic numerical approach to the stability analysis of nonlinear parametric excited systems with multi-degree-of-freedom is developed and the stability of a nonlinear vibration system depends on the dynamic behavior of its perturbation. The nonlinear parameter-varying differential equations for the perturbation motion are expressed in the form of Hamiltonian equations with time-varying Hamiltonian, and are converted further into the classical Hamiltonian equations with extended time-invariant Hamiltonian by augmenting the state variables. The solution to the augmented Hamiltonian equations has the symplectic structure in terms of the symplectic transformation. Then the difference equations of the symplectic Runge-Kutta algorithm with a sufficient condition are constructed, which is proved to preserve the intrinsic symplectic structure of the original solution. In particular, the symplectic Gauss-Runge-Kutta algorithm with stage 2 and order 4 is proposed and applied to the stability analysis of a nonlinear system. Unstable regions based on the nonlinear periodic-parameter perturbation equation are obtained by using the symplectic Gauss-Runge-Kutta algorithm, analytical solution method and non-symplectic conventional Runge-Kutta algorithm to verify the higher accuracy of the proposed algorithm. Unstable regions based on the nonlinear perturbation are given to illustrate the improvement over those based on the linear perturbation. The developed symplectic approach to the stability analysis can preserve the symplectic structure of the original system and is applicable to nonlinear parametric excited systems with multi-degree-of-freedom. [ABSTRACT FROM AUTHOR]

The Tsing Ma Bridge in Hong Kong is suspension bridge with a main span of 1377 m carrying both highway and railway traffic. After completing its construction in 1997, the bridge was instrumented by the Hong Kong SAR Government Highways Department with a long-term structural health monitoring system comprising about 300 sensors permanently installed on the bridge. As part of this monitoring system, a total of 110 strain gauges have been installed to measure strain at the deck cross-sections and bearings. In this study, a method for real-time structural performance evaluation of the stiffening deck system making use of long-term strain measurement data is proposed and verified using the strain monitoring data from a typical deck cross-section of the Tsing Ma Bridge. [ABSTRACT FROM AUTHOR]

The cable-stayed Ting Kau Bridge has been permanently instrumented with more than 230 sensors for long-term structural health monitoring. In this article, the feasibility of using the measured dynamic characteristics of the bridge for damage detection is studied. Making use of a validated three-dimensional (3D) finite element model (FEM), modal flexibility matrices of the bridge are constructed using a few truncated modes and incomplete modal vectors at the sensor locations. The relative flexibility change (RFC) between intact and damage states is then formulated as an index to locate damage. The applicability of this flexibility index for damage location in the cable-stayed bridge is examined by investigating various damage scenarios including those at stay cables, longitudinal stabilizing cables, bearings and supports, longitudinal girders and cross girders, and taking into account measurement noise in modal data. The influence of two ambient factors, that is, temperature change and traffic loading, on the damage detectability is also analyzed by approximately considering an equivalent alteration in the material and structural behaviors. It is revealed that in the absence of ambient effects the RFC index performs well for locating damage of different severities in single-damage cases. In multi-damage cases the RFC index may provide false-negative identification for damage at the members with low sensitivity. Eliminating ambient effects is requisite for reliable detection of damage at stay cables and cross girders. The capability of the RFC index for locating damage at cross girders is significantly dropped in the presence of measurement noise. [ABSTRACT FROM AUTHOR]

A good understanding of environmental effects on structural modal properties is essential for reliable performance of vibration-based damage diagnosis methods. In this paper, a method of combining principal component analysis (PCA) and support vector regression (SVR) technique is proposed for modeling temperature-caused variability of modal frequencies for structures instrumented with long-term monitoring systems. PCA is first applied to extract principal components from the measured temperatures for dimensionality reduction. The predominant feature vectors in conjunction with the measured modal frequencies are then fed into a support vector algorithm to formulate regression models that may take into account thermal inertia effect. The research is focused on proper selection of the hyperparameters to obtain SVR models with good generalization performance. A grid search method with cross validation and a heuristic method are utilized for determining the optimal values of SVR hyperparameters. The proposed method is compared with the method directly using measurement data to train SVR models and the multivariate linear regression (MLR) method through the use of long-term measurement data from a cable-stayed bridge. It is shown that PCA-compressed features make the training and validation of SVR models more efficient in both model accuracy and computational costs, and the formulated SVR model performs much better than the MLR model in generalization performance. When continuously measured data is available, the SVR model formulated taking into account thermal inertia effect can achieve more accurate prediction than that without considering thermal inertia effect. [ABSTRACT FROM AUTHOR]

A procedure for assessment of bridge expansion joints making use of long-term monitoring data is presented in this paper. Based on the measurement data of expansion joint displacement and bridge temperature, the normal correlation pattern between the effective temperature and thermal movement is first established. Alarms will be raised if a future pattern deviates from this normal pattern. With the established correlation pattern, the expansion joint displacements under the design maximum and minimum temperatures are predicted and compared with the design allowable values for validation. The extreme temperatures for a certain return period are also derived using the measurement data for design verification. Then the annual or daily-average cumulative movements experienced by expansion joints are estimated from the monitoring data for comparison with the expected values in design. Because the service life and interval for replacement of expansion joints rely to a great extent on the cumulative displacements, an accurate prediction of the cumulative displacements will provide a robust basis for determining a reasonable interval for inspection or replacement of expansion joints. The proposed procedure is applied to the assessment of expansion joints in the cable-stayed Ting Kau Bridge with the use of one-year monitoring data. [ABSTRACT FROM AUTHOR]

A direct numerical approach for solving the instability problem of multi-degree-of-freedom dynamic systems with general period-parameter excitation is developed based on the Floquet theory, Fourier series and generalized eigenvalue analysis. The developed direct numerical approach to the instability is applied to an inclined stay cable with sag under periodic two-support-motion excitation. The partially differential equation for the parametrically excited vibration of the cable is derived by using the transformation of displacements and converted into ordinary differential equations according to the Galerkin method. The unstable regions for parametrically excited vibration of the damped cable system with multi-degree-of-freedom are obtained to illustrate its overall instability. The effects of each mode vibration and parameters of the cable on the unstable regions are analyzed. The developed direct numerical approach to the parametrically excited instability is applicable to more general periodic parameter-excited systems. [ABSTRACT FROM AUTHOR]

This article presents the theoretical and in situ experimental studies on state-derivative feedback control of bridge cable vibration using semiactive magnetorheological (MR) dampers. The semiactive feedback control is accomplished using only one MR damper and one accelerometer collocated near the lower end of the cable. Within the framework of reciprocal state space (RSS), the linear quadratic regulator (LQR) control technique is applied to formulate state-derivative feedback control law and derive the feedback and estimator gains for real-time control of cable vibration using MR dampers. The state-derivative feedback control strategy directly uses acceleration information for feedback and state estimation, which is usually the only measure available in practical cable vibration control implementation. More importantly, the control force commanded by the state-derivative feedback control strategy based on energy weighting is a dissipative force except for low velocity and small force, which is therefore implementable by the semiactive MR dampers without clipping. Numerical simulations of state-derivative feedback control for a stay cable in the cable-stayed Dongting Lake Bridge are conducted under sweeping sine excitation and sinusoidal step relaxation excitation, and then the experimental validation of the prototype cable is carried out in the bridge site with the help of the real-time control system dSPACE. Good agreement between the simulation and experimental results is observed. [ABSTRACT FROM AUTHOR]

A recent trend in the design of long-span bridges is multispan cable-stayed bridges with three or more towers. A critical problem of multispan cable-stayed bridges is the stabilization of the central tower(s), which has resulted in increasing application of stabilizing cables. The Ting Kau Bridge in Hong Kong is one of a few multispan cable-stayed bridges adopting stabilizing cables ever built. In this article, the dynamic properties of multispan cable-stayed bridges with stabilizing cables and the effect of stabilizing cables on bridge seismic response are studied by referring to the Ting Kau Bridge. Based on a validated 3D finite-element model, modal analysis is conducted which shows that the longitudinal stabilizing cables bring about a number of global modes with strong modal interaction among the deck, towers, and cables. The seismic response and internal force in the central tower are found to be much larger than those in the side towers. The longitudinal stabilizing cables are very effective in reducing the internal force in the central tower generated by longitudinal earthquake excitation, but insignificantly affect the seismic response in the bridge deck and side towers. As a whole, the stabilizing cables act favorably in the reduction of seismic response of the bridge. [ABSTRACT FROM AUTHOR]

For the purpose of developing a vibration-based tension force evaluation procedure for bridge cables using measured multimode frequencies, an investigation on accurate finite element modelling of large-diameter sagged cables taking into account flexural rigidity and sag extensibility is carried out in this paper. A three-node curved isoparametric finite element is formulated for dynamic analysis of bridge stay cables by regarding the cable as a combination of an “ideal cable element” and a fictitious curved beam element in the variational sense. With the developed finite element formulation, parametric studies are conducted to evaluate the relationship between the modal properties and cable parameters lying in a wide range covering most of the cables in existing cable-supported bridges, and the effect of cable bending stiffness and sag on the natural frequencies. A case study is eventually provided to compare the measured natural frequencies of main cables of the Tsing Ma Bridge and the computed frequencies with and without considering cable bending stiffness. The results show that ignoring bending stiffness gives rise to unacceptable errors in predicting higher order natural frequencies of the cables, and the proposed finite element formulation provides an accurate baseline model for cable tension identification from measured multimode frequencies. [Copyright &y& Elsevier]

Presents a nonparametric identification method for nonlinear hysteretic systems. Importance of hysteretic behavior modeling; Mapping of hysteretic restoring force; Information on nonparametric identification.

An introduction is presented in which the editor discusses various reports within the issue on topics including railway bridges, wind vehicle-bridge coupling system and railway tunnels.

The long-term performance of engineering structures in a corrosive environment will be significantly affected by the coupled action of corrosion and fatigue. In this article, a probabilistic corrosion fatigue analytical model is proposed by taking into account the effects of corrosion-induced reduction of the cross-sectional area and deterioration of the fatigue strength of structural components. The proposed model is exemplified to evaluate the probabilistic corrosion fatigue life of a typical welded joint in the suspension Tsing Ma Bridge instrumented with a long-term structural health monitoring system. A genetic algorithm-based mixture parameter estimation method is developed to facilitate the multimodal modeling of stress spectrum derived from the long-term monitoring data of dynamic strain. The achieved results demonstrate that with the increase in the service life, the reliability index of the investigated typical welded joint is dramatically reduced under the combined effect of corrosion and fatigue. [ABSTRACT FROM AUTHOR]

This paper presents train-induced dynamic response and fatigue damage analyses for the hangers of a tied-arch railway bridge. A train–bridge interaction analysis is carried out using the vector form intrinsic finite element method, through which the inertial force effect of the moving train can be effectively analyzed. The responses of the bridge deck and its hangers are investigated at resonant train speeds. Significantly larger stresses are observed on the shorter hangers near the arch anchorages, which is primarily caused by the first two anti-symmetrical vibration modes. The fatigue damage to the hangers is estimated using the Palmgren-Miner model (PMM) for linear fatigue damage accumulation and the continuum damage mechanics (CDM) method for nonlinear accumulation. The mean stress effect is considered in the S–N curve primarily by Smith–Watson–Topper equation in terms of the effective stress range with a zero-mean stress. Two probability distributions for train speed are considered for the current and future operating conditions with mean speeds of 220 and 300 km/h, respectively. This study found that the fatigue lives estimated by the nonlinear CDM are significantly shorter than those estimated by the linear PMM. It also found that the shortest hanger reflects the shortest fatigue life at the current operating speed, whereas the longer hanger near the third point of the bridge deck may have the shortest fatigue life at an increased speed in the future. [ABSTRACT FROM AUTHOR]

A stochastic averaging method for strongly non-linear oscillators under external and/or parametric excitation of bounded noise is proposed by using the so-called generalized harmonics functions. The method is then applied to study the primary resonance of Duffing oscillator with hardening spring under external excitation of bounded noise. The stochastic jump and its bifurcation of the system are observed and explained by using the stationary probability density of amplitude and phase. Subsequently, the method is applied to study the dynamical instability and parametric resonance of Duffing oscillator with hardening spring under parametric excitation of bounded noise. The primary unstable region is delineated by evaluating the Lyapunov exponent of linearized system, and the response and jump of non-linear system around the unstable region are examined by using the sample functions and stationary probability density of amplitude and phase. [Copyright &y& Elsevier]

The response of Duhem hysteretic system to externally and/or parametrically non-white random excitations is investigated by using the stochastic averaging method. A class of integrable Duhem hysteresis models covering many existing hysteresis models is identified and the potential energy and dissipated energy of Duhem hysteretic component are determined. The Duhem hysteretic system under random excitations is replaced equivalently by a non-hysteretic non-linear random system. The averaged Ito''s stochastic differential equation for the total energy is derived and the Fokker–Planck–Kolmogorov equation associated with the averaged Ito''s equation is solved to yield stationary probability density of total energy, from which the statistics of system response can be evaluated. It is observed that the numerical results by using the stochastic averaging method is in good agreement with that from digital simulation. [Copyright &y& Elsevier]

An approximate method for analyzing the response of Preisach hysteretic systems with non-local memory under stationary Gaussian excitation is proposed. The covariance matrix equation of system response is derived. The cross correlation function of Preisach hysteretic force and response in the covariance equation is evaluated based on the switching probability analysis and the Gaussian approximation of response process and an explicit expression for the cross correlation function is given for the case of symmetric Preisach weighting function. It is shown that the numerical result obtained by using the proposed method is in good agreement with that from digital simulation. [Copyright &y& Elsevier]

State-space (SS) model is proposed to identify the time lag between the asynchronous accelerations at different locations of the Jiangyin Bridge measured during a ship-bridge collision. One of the accelerations is chosen as the reference signal, and the time axis of the rest of them are shifted relative to that of the reference signal with a series of shifting times. For each pair of reference and time shifted signals, SS models in correspondence to the shifting time series are formulated. Their system matrices are identified with data-driven stochastic subspace identification algorithm, and their model order is determined by Akaike's information theoretic criterion and final prediction error. If the 2 accelerations for model fitting are asynchronous, errors may be introduced into the SS model and its prediction error is expected to be greater than the counterpart obtained with synchronous accelerations. Therefore, the actual time lag between them is identified from the shifting time that corresponds to the minimum of loss function, which is used to map the prediction error vector sequence to a real number. In addition, asynchronous acceleration data measured 2 hr ahead of the ship-bridge collision and synchronous acceleration data measured long after the ship-bridge collision are also analyzed. The former dataset is exploited to evaluate the reproducibility of the SS model for time synchronization, and the latter dataset is utilized to examine its anti-false-identification capability. The results show that the SS model achieves a satisfactory performance in the identification of time lag for both asynchronous and synchronous measurement data. [ABSTRACT FROM AUTHOR]

This paper presents the experimental modal analysis of the Canton Tower from the ambient vibration measurements under different earthquake excitation conditions. Firstly, the time history and Power Spectral Density (PSD) of the acceleration response under different earthquake excitations have been compared. Secondly, two output-only modal identification techniques are applied to the field measurements under earthquake excitations to identify the dynamic properties of the tower, namely, the Frequency Domain Decomposition (FDD) and the Subspace Stochastic Identification (SSI). At last, the Hilbert-Huang transform (HHT) method is applied to obtain the instantaneous frequencies and energy distribution under different loadings in the time-frequency domain and the results are compared with those from wavelet transform. The modal properties of the Canton Tower presented in this paper can be used as baseline for structural health monitoring and the analysis of dynamic characteristic of the high-rise structures under different earthquake excitations in future. [ABSTRACT FROM AUTHOR]

A method for structural response data reconstruction based on a generalized orthogonal polynomial function is presented in this paper. The method can be used to generate the displacement and velocity responses from the measurements of acceleration responses. And it can also be utilized to obtain the displacement and velocity responses from the measurements of strain responses. Two numerical examples are used to illustrate the correctness and accuracy of the proposed method. The proposed method is further verified by a field measurement of Canton Tower. The displacement time histories generated from the measured acceleration are found to agree well with the displacement time histories from global position system measurement. [ABSTRACT FROM AUTHOR]

The Tsing Ma Bridge is a cable suspension bridge carrying both highway and railway. A bridge health monitoring system called wind and structural health monitoring system (WASHMS) has been installed in the Tsing Ma Bridge and operated since 1997 to monitor the structural performance and its associated loads and environments. However, there exists a possibility that the worst structural conditions may not be directly monitored due to the limited number of sensors and the complexity of structure and loading conditions. Therefore, it is an essential task to establish structural performance relationships between the critical locations/components of the bridge and those instrumented by the WASHMS. Meanwhile, to develop and validate practical and effective structural damage detection techniques and safety evaluation strategies, the conventional modeling for cable-supported bridges by approximating the bridge deck as continuous beams or grids is not applicable for simulation of real damage scenarios. To fulfil these tasks, a detailed full three-dimensional (3D) finite element model of the Tsing Ma Bridge is currently established for direct computation of the stress/strain states for all important bridge components. This paper presents the details of establishing this full 3D finite element model and its calibration. The major structural components are modeled in detail and the connections and boundary conditions are modeled properly, which results in about half million elements for the complete bridge model. The calibration of vibration modes and stresses/strains due to passing trains is carried out, and a good agreement is found between the computed and measured results. [ABSTRACT FROM AUTHOR]