Sutong Cable-stayed Bridge Research Articles

Stationary and non-stationary buffeting analyses of a long-span bridge under typhoon winds

The buffeting response is a vital consideration for long-span bridges in typhoon-prone areas. In the conventional analysis, the turbulence and structural vibrations are assumed as stationary processes, which are, however, inconsistent with the non-stationary features observed in typhoon winds. This poses a question on how the stationary assumption would affect the evaluation of buffeting responses under non-stationary wind actions in nature. To figure out this problem, this paper presents a comparative study on buffeting responses of a long-span cable-stayed bridge based on stationary and non-stationary perspectives. The stationary and non-stationary buffeting analysis frameworks are firstly reviewed. Then, a modal analysis of the example bridge, Sutong Cable-stayed Bridge (SCB), is conducted, and stationary and non-stationary spectral models are derived based on measured typhoon winds. On this condition, the buffeting responses of SCB are finally analyzed by following stationary and non-stationary approaches. Although the stationary results are almost identical with the non-stationary results in the mean sense, the root-mean-square value of buffeting responses are underestimated by the stationary assumption as the timevarying features existing in the spectra of turbulence are neglected. The analytical results highlights a transition from stationarity to non-stationarity in the buffeting analysis of long-span bridges.

Time history analysis-based nonlinear finite element model updating for a long-span cable-stayed bridge

Accurate finite element models play significant roles in the design, health monitoring and life-cycle maintenance of long-span bridges. However, due to uncertainties involved in finite element modelling, updating of the finite element model to best represent the real bridge is inevitable. This is particularly true after a long-span bridge experiences a moderate or severe earthquake and suffers some damage. This study thus proposes a time history analysis-based nonlinear finite element model updating method for long-span cable-stayed bridges. Special efforts are made to (1) establish the response time history-based objective functions and associated acceptance criteria, (2) conduct comprehensive sensitivity analyses to select appropriate nonlinear updating parameters and (3) develop a highly efficient cluster computing-aided optimization algorithm. A scaled structure of the Sutong cable-stayed bridge in China is adopted as a case study. Three nonlinear test cases performed in the shake table tests of the scaled bridge are used to validate the feasibility and accuracy of the proposed method. A good agreement is observed between the simulated response time histories and the measured response time histories for the scaled bridge under both moderate and strong ground motions. The proposed method could provide an accurate nonlinear finite element model for better performance assessment, damage detection and life-cycle maintenance of long-span cable-stayed bridges.

Temperature distribution analysis of steel box-girder based on long-term monitoring data

Temperature may have more significant influences on structural responses than operational loads or structural damage. Therefore, a comprehensive understanding of temperature distributions has great significance for proper design and maintenance of bridges. In this study, the temperature distribution of the steel box girder is systematically investigated based on the structural health monitoring system (SHMS) of the Sutong Cable-stayed Bridge. Specifically, the characteristics of the temperature and temperature difference between different measurement points are studied based on field temperature measurements. Accordingly, the probability density distributions of the temperature and temperature difference are calculated statistically, which are further described by the general formulas. The results indicate that: (1) the temperature and temperature difference exhibit distinct seasonal characteristics and strong periodicity, and the temperature and temperature difference among different measurement points are strongly correlated, respectively; (2) the probability density of the temperature difference distribution presents strong non-Gaussian characteristics; (3) the probability density function of temperature can be described by the weighted sum of four Normal distributions. Meanwhile, the temperature difference can be described by the weighted sum of Weibull distribution and Normal distribution.

Automated modal identification using principal component and cluster analysis: Application to a long‐span cable‐stayed bridge

Obtaining timely information about the health of civil infrastructure is critical to ensuring safe and reliable operation. Structural health monitoring has been proposed as a means to provide such information; however, most structural health monitoring systems provide only raw data, rather than actionable information. It is necessary to develop automated modal analysis strategies that can provide near real-time dynamic information regarding the in-service state of a bridge, which is essential to vibration control, finite element model calibration, and damage detection for safety and serviceability condition assessment. This study presents an automated framework to extract structural modal parameters from the stabilization diagram using a parametric modal identification method such as stochastic subspace identification. The framework focuses on the automated modal analysis issues of an in-service long-span bridge with close-frequency modes. The presented framework is validated using experimental tests of a 1.8-m 18-story laboratory model. Subsequently, data from Sutong Cable-Stayed Bridge are employed to demonstrate its potential usage in the field. Finally, an application of the automated framework is presented to identify and track the modal parameters of the deck of Sutong Cable-Stayed Bridge for 20 days. Results show that the presented framework can successfully extract the structural modal parameters with good accuracy and robustness, hence can provide a reliable technical support for in-service monitoring of long-span bridges.

Investigation of dynamic properties of long-span cable-stayed bridges based on one-year monitoring data under normal operating condition

Environmental factors, such as temperature, traffic, and wind, play an important role on the variations of dynamic properties of long-span cable-stayed bridges. The dynamic characteristics of Sutong Cable-Stayed Bridge (SCB), including acceleration and strain responses as well as modal frequencies, are investigated using one-year continuous monitoring data under operating conditions by the structural health monitoring system. The in situ wind characteristics and structural temperature behavior of SCB are also analyzed. More than 99% of the wind speed values are smaller than 16 m/s; and the largest temperature variation of the main girder exceeds 60 °C. Besides, acceleration and strain, root mean square (RMS) data are both normalized using the Z-score standardization method. Relation analysis between the normalized acceleration and strain RMS values is conducted based on the time-history comparison and linear least square fitting. Results show that both of the processed acceleration and strain RMS values could properly describe the variation trend of the traffic load, although variation amplitudes of the two normalized parameters differ from each other. In addition, one-year continuous modal frequencies of SCB are identified using Hilbert–Huang transform method. Variability analysis of the structural modal frequencies due to environmental temperature and operational traffics is then conducted. Results show that temperature is the most important environmental factor for vertical and torsional modal frequencies. The traffic load is the second critical factor especially for the fundamental vertical frequency of SCB. Research results could provide references for damage detection and safety evaluation for similar long-span cable-stayed bridges.

PROBABILITY MODEL AND RELIABILITY ANALYSIS OF CABLE STRESS FOR CABLE-STAYED BRIDGE

The aim of this paper is to investigate the time-varying effect of stay cable of long-span cable-stayed bridges subject to vehicle load. The analysis has been carried out on the Su-Tong cable-stayed bridge in Jiangsu, China that has the second-longest span among the completed composite-deck cable-stayed bridges in the world currently. Probability models of vehicle load in each lane (fast lane, middle lane and slow lane) and cable stress under random vehicle load were developed based on the stochastic process theory. The results show the gross vehicle weight follows lognormal distribution or multi-peak distribution, and the time-interval of the vehicle follows a lognormal distribution. Then, the probability function of maximum cable stress was determined using up-crossing theory. Finally, the reliability of stay cable under random vehicle load was analysed. The reliability index ranges from 9.59 to 10.82 that satisfies the target reliability index of highway bridge structure of finished dead state.

Seismic responses of super-span cable-stayed bridges induced by ground motions in different sites relative to fault rupture considering soil-structure interaction

The focus of this paper is to evaluate the seismic response of a cable-stayed bridge built in fault zones considering soil-structure interaction (SSI) effects. Bridges crossing fault-rupture zones may be built in the Forward Region (FR), Middle Region (MR) and Backward Region (BR) relative to the possible position of the fault. Three groups of ground motions (51 records in two orthogonal directions) in above regions are selected as the input from the 1999 Taiwan Chi-Chi earthquake based on the sites relative to the fault rupture. The Sutong Cable-stayed Bridge (SCB) is taken as an example. Two models are used in this study, i.e. the fixed-base bridge and the bridge with SSI effects where four different orientation angles (0°, 30°, 60°, and 90°) have been considered compared to the fault direction. Systematic lumped-parameter models are utilized to represent the dynamic behavior of the foundation supported on soil. The results reveal that the seismic behavior of the SCB in those 3 regions shows significant differences. The SSI effects affect the bridge response through a systematic decrease of all modal frequencies and a substantial change in nature of dominant shapes especially for the higher modes of vibrations. The displacement of such bridges may be underestimated if the SSI effects are ignored. The orientation of the bridge axis relative to fault trace influences the seismic responses of the bridges in fault regions. The bridge located in MR experiences larger responses than that in FR and BR. Due to the high values of velocity spectra, velocity-related intensity measures i.e. peak ground velocity (PGV) and the ratio of PGV to peak ground acceleration (PGA) show strong correlation with the seismic responses of the bridge located in FR. Since the records in MR and BR have high acceleration spectra, PGV and PGA correlate well with the responses of the bridge located in MR and BR.

Wind characteristics at Sutong Bridge site using 8-year field measurement data

Full-scale wind characteristics based on the field measurements is an essential element in structural wind engineering. Statistical analysis of the wind characteristics at Sutong Cable-stayed Bridge (SCB) site is conducted in this study with the recorded long-term wind data from structural health monitoring system (SHMS) between 2008 and 2015. Both the mean and turbulent wind characteristics and power spectra are comprehensively investigated and compared with those in the current codes of practice, such as the measured wind rose diagram, monthly maximum mean wind speed, turbulence intensity, integral length scale. Measurement results based on the monitoring data show that winds surrounding the SCB site are substantially influenced by the southeast monsoon in summer and strong northern wind in winter. The measured turbulence intensity is slightly higher than the recommended values in specifications, while the measured ratio of lateral to longitudinal turbulence intensity is slightly lower. An approximately linear relationship between the measured turbulence intensities and gust factors is obtained. The mean value of the turbulence integral length scale is smaller than that of typical typhoon events. In addition, it is found that the Kaimal spectrum is suitable to be adopted as the power spectrum for longitudinal wind component at the SCB site. This contribution would provide important wind characteristic references for the wind performance evaluation of SCB and other civil infrastructures in adjacent regions.

Longitudinal seismic response control of long-span cable-stayed bridges using shape memory alloy wire-based lead rubber bearings under near-fault records

This article investigates the efficiency of a new generation smart isolation system, namely shape memory alloy wire-based lead rubber bearing, for the seismic response control of long-span cable-stayed bridge systems under near-fault ground motions. The constitutive model of shape memory alloy wire-based lead rubber bearings is coded and implemented into OpenSees as a new user element. This user element can accurately predict the re-centering capability and energy dissipation capacity of shape memory alloy wire-based lead rubber bearing under different excitations. The Sutong cable-stayed bridge in China, with a main span of 1088 m, is taken as an example. Results reveal that implementing shape memory alloy wires into lead rubber bearings can effectively increase the self-centering property and, as a result, reduce the residual deformation in shape memory alloy wire-based lead rubber bearings under near-fault ground motions. Shape memory alloy wires lead to an increase in the horizontal stiffness and energy dissipation capacity of shape memory alloy wire-based lead rubber bearings. The deck displacement is restricted effectively, and a superior structural performance is achieved in terms of the deck acceleration. Shape memory alloy wire-based lead rubber bearings can effectively reduce the base shear and base moment of the towers. However, it is observed that an increase in the shape memory alloy wire diameter may have negligible effect on the deck acceleration, tower base shear and moment, and in some cases, on the pier base shear and moment.

Effects of Near-Fault Motions and Artificial Pulse-Type Ground Motions on Super-Span Cable-Stayed Bridge Systems

AbstractThis paper evaluates the seismic responses of a super-span cable-stayed bridge subjected to near-fault ground motions. A new method, record-decomposition incorporation (RDI), is proposed to synthesize the artificial near-fault pulse-type ground motions by combining the high-frequency background record (BGR) with simple equivalent pulses. The effects of forward-directivity pulses and fling-step pulses on the responses are assessed for the Sutong cable-stayed bridge (with a main span of 1,088 m) in China. The results show that the near-fault pulse-type ground motions generate larger displacement and internal force to the bridge compared with the nonpulse ground motions, and the fling-step ground motions are more damaging to the bridge than those of the forward-directivity ground motions. The high-frequency components of near-fault records have a significant effect on the responses of the bridge. Subsequently, the longitudinal displacement and bending moment of the tower induced by artificial ground ...

Structural health monitoring system for Sutong Cable-stayed Bridge

Structural Health Monitoring System (SHMS) works as an efficient platform for monitoring the health status and performance deterioration of engineering structures during long-term service periods. The objective of its installation is to provide reasonable suggestions for structural maintenance and management, and therefore ensure the structural safety based on the information extracted from the real-time measured data. In this paper, the SHMS implemented on a world-famous kilometer-level cable-stayed bridge, named as Sutong Cable-stayed Bridge (SCB), is introduced in detail. The composition and core functions of the SHMS on SCB are elaborately presented. The system consists of four main subsystems including sensory subsystem, data acquisition and transmission subsystem, data management and control subsystem and structural health evaluation subsystem. All of the four parts are decomposed to separately describe their own constitutions and connected to illustrate the systematic functions. Accordingly, the main techniques and strategies adopted in the SHMS establishment are presented and some extension researches based on structural health monitoring are discussed. The introduction of the SHMS on SCB is expected to provide references for the establishment of SHMSs on long-span bridges with similar features as well as the implementation of potential researches based on structural health monitoring.

Wind power spectra for coastal area of East Jiangsu Province based on SHMS

A wind velocity power spectrum (WVPS) with high fidelity is extremely important for accurate prediction of structural buffeting response. WVPS heavily depends on the geographical locations, local terrains and topographies. Hence, field measurement of wind characteristics may be the unique way to obtain the accurate WVPS for a specific region. In this paper, a systematic analysis and discussions of existing WVPSs were performed. Six recorded strong wind data from the structural health monitoring systems (SHMS) of Runyang Suspension Bridge (RSB) and Sutong Cable-stayed Bridge (SCB) in Jiangsu Province of China were selected for analysis. The measured and pre-processed wind velocity data was first transformed from time domain to frequency domain to obtain the measured spectrum. The spectrum for each strong wind was then fitted using the nonlinear least square method and compared with both the fitted spectrum from statistical analysis and the recommended spectrum in specifications. The modified Kaimal spectrum was proved to be the best choice for the coastal area of East Jiangsu Province. Finally, a suitable WVPS formula fit for the coastal area of East Jiangsu Province was presented based on the modified Kaimal spectrum. Results in this study provide a more accurate and reliable WVPS for wind-resistant design of engineering structures in the coastal area of East Jiangsu Province.

Modal Identification of Sutong Cable-Stayed Bridge during Typhoon Haikui Using Wavelet Transform Method

AbstractIn order to provide a realistic basis for structural damage identification and safety evaluation of long-span bridges, the modal parameters of a kilometer-scale cable-stayed bridge are identified using the wavelet transform (WT) method. Sutong cable-stayed bridge (SCB), which was excited by typhoon Haikui, was taken as the research object. Based on the structural vibration responses recorded by structural health monitoring system (SHMS) of SCB, modal parameters including the frequency and the damping ratio of the bridge were identified using the WT method. Four vertical, two torsional, and one lateral modes were selected for analysis. After comparing the analysis results with those from the related references, the whole-process variation of modal parameters of the SCB during typhoon Haikui was investigated. Furthermore, the relationship between modal parameters and wind speed was analyzed. Results show that the modal parameter identification based on the WT method is stable and reliable. The influ...

Numerical Analysis of Long-Span Cable-Stayed Bridge in the Construction Phase

The fabrication and erection of cable-stayed bridges involve major changes in structure configuration through the addition and removal of structure components. In every stage of the construction process, adequate information on the constructed structure is important to determine the real structure situation for the analysis of errors and to verify construction requirements. The ultimate goals are to meet construction needs and identify the effects of modification in subsequent construction procedures. The final configuration of the structure is strongly dependent on the construction and fabrication procedures. In this regard, developing an FEA model to simulate the actual construction processes is necessary to determine the performance of a bridge under external loads. In this study, a general methodology for construction processes is presented to simulate a cable-stayed bridge. The stage-by-stage construction of the Sutong Bridge is simulated with ANSYS software package. The tensions of cables are realized with ANSYS parametric design language, element birth and death function, and mutliframe restart function. The objective of the construction stage simulation is to identify stresses and deformations of the steel box girder and the concrete towers, as well as the cable tension stress, to meet the design requirements. Results of the construction stage analysis showed that the temperature method could simulate the adjustment of the inclined cable force successfully, and the global stiffness of the Sutong Bridge was very small before closure. These findings served as the initial data for a dynamic research on the Sutong cable-stayed bridge.

Joint distribution of wind speed and direction in the context of field measurement

The joint distribution of wind speed and wind direction at a bridge site is vital to the estimation of the basic wind speed, and hence to the wind-induced vibration analysis of long-span bridges. Instead of the conventional way relying on the weather stations, this study proposed an alternate approach to obtain the original records of wind speed and the corresponding directions based on field measurement supported by the Structural Health Monitoring System (SHMS). Specifically, SHMS of Sutong Cable-stayed Bridge (SCB) is utilized to study the basic wind speed with directional information. Four anemometers are installed in the SHMS of SCB: upstream and downstream of the main deck center, top of the north and south tower respectively. Using the recorded wind data from SHMS, the joint distribution of wind speed and direction is investigated based on statistical methods, and then the basic wind speeds in 10-year and 100-year recurrence intervals at these four key positions are calculated. Analytical results verify the reliability of the recorded wind data from SHMS, and indicate that the joint probability model for the extreme wind speed at SCB site fits well with the Weibull model. It is shown that the calculated basic wind speed is reduced by considering the influence of wind direction. Compared to the design basic wind speed in the Specification of China, basic wind speed considering the influence of direction or not is much smaller, indicating a high safety coefficient in the design of SCB. The results obtained in this study can provide not only references for further wind-resistance research of SCB, but also improve the understanding of the safety coefficient for wind-resistance design of other engineering structures in the similar area.

Long-Term Temperature Monitoring and Statistical Analysis on the Flat Steel-Box Girder of Sutong Bridge

AbstractUsing the flat steel-box girder of China’s Sutong Cable-stayed Bridge as a research object, its temperature field is long-term monitored and analyzed based on bridge’s structural health mon...

A simulation study on the optimal control of buffeting displacement for the Sutong Bridge with multiple tuned mass dampers

The buffeting of long-span cable-supported bridges under strong winds is one of the key issues in bridge wind engineering. In order to study the effectiveness of the multiple tuned mass dampers (MTMDs) in buffeting control of long-span bridges, the Sutong Cable-stayed Bridge (SCB) with a main span of 1088 m in China is taken as an example in this paper. The spatial finite element model of the SCB is established and the modal analysis is conducted based on ANSYS. After the 3D turbulence wind field of the SCB is simulated using the measured wind parameters, the time-domain buffeting analysis on the SCB is conducted with the aerodynamic self-excited forces included. According to the dynamic characteristics and the time-domain buffeting analysis results of the SCB, the parameter sensitivity analysis on buffeting vibration control with MTMD is conducted in ANSYS. The optimum parameters are then obtained with the construction difficulty and economic factors considered. Results show that the control efficiency is sensitive to the number of the TMD, mass ratio, frequency band-width ratio, and damping ratio. Both the vertical and the lateral vibrations can be effectively controlled when proper design parameters of a MTMD system are used. In addition, the control effect on lateral vibration is better than that on vertical vibration. Results obtained in this study can provide references for anti-wind design and buffeting control of long-span cable-stayed bridges.

Influence of structural parameters on dynamic characteristics and wind-induced buffeting responses of a super-long-span cable-stayed bridge

A 3D finite element (FE) model for the Sutong cable-stayed bridge (SCB) is established based on ANSYS. The dynamic characteristics of the bridge are analyzed using a subspace iteration method. Based on recorded wind data, the measured spectra expression is presented using the nonlinear least-squares regression method. Turbulent winds at the bridge site are simulated based on the spectral representation method and the FFT technique. The influence of some key structural parameters and measures on the dynamic characteristics of the bridge are investigated. These parameters include dead load intensity, as well as vertical, lateral and torsional stiffness of the steel box girder. In addition, the influence of elastic stiffness of the connection device employed between the towers and the girder on the vibration mode of the steel box girder is investigated. The analysis shows that all of the vertical, lateral and torsional buffeting displacement responses reduce gradually as the dead load intensity increases. The dynamic characteristics and the structural buffeting displacement response of the SCB are only slightly affected by the vertical and torsional stiffness of the steel box girder, and the lateral and torsional buffeting displacement responses reduce gradually as the lateral stiffness increases. These results provide a reference for dynamic analysis and design of super-long-span cable-stayed bridges.

Full-scale measurements and system identification on Sutong cable-stayed bridge during Typhoon Fung-Wong.

The structural health monitoring system (SHMS) provides an effective tool to conduct full-scale measurements on existing bridges for essential research on bridge wind engineering. In July 2008, Typhoon Fung-Wong lashed China and hit Sutong cable-stayed bridge (SCB) in China. During typhoon period, full-scale measurements were conducted to record the wind data and the structural vibration responses were collected by the SHMS installed on SCB. Based on the statistical method and the spectral analysis technique, the measured data are analyzed to obtain the typical parameters and characteristics. Furthermore, this paper analyzed the measured structural vibration responses and indicated the vibration characteristics of the stay cable and the deck, the relationship between structural vibrations and wind speed, the comparison of upstream and downstream cable vibrations, the effectiveness of cable dampers, and so forth. Considering the significance of damping ratio in vibration mitigation, the modal damping ratios of the SCB are identified based on the Hilbert-Huang transform (HHT) combined with the random decrement technique (RDT). The analysis results can be used to validate the current dynamic characteristic analysis methods, buffeting calculation methods, and wind tunnel test results of the long-span cable-stayed bridges.

Mathematical Modeling for Lateral Displacement Induced by Wind Velocity Using Monitoring Data Obtained from Main Girder of Sutong Cable-Stayed Bridge

Based on the health monitoring system installed on the main span of Sutong Cable-Stayed Bridge, GPS displacement and wind field are real-time monitored and analyzed. According to analytical results, apparent nonlinear correlation with certain discreteness exists between lateral static girder displacement and lateral static wind velocity; thus time series of lateral static girder displacement are decomposed into nonlinear correlation term and discreteness term, nonlinear correlation term of which is mathematically modeled by third-order Fourier series with intervention of lateral static wind velocity and discreteness term of which is mathematically modeled by the combined models of ARMA(7,4)and EGARCH(2,1). Additionally, stable power spectrum density exists in time series of lateral dynamic girder displacement, which can be well described by the fourth-order Gaussian series; thus time series of lateral dynamic girder displacement are mathematically modeled by harmonic superposition function. By comparison and verification between simulative and monitoring lateral girder displacements from September 1 to September 3, the presented mathematical models are effective to simulate time series of lateral girder displacement from main girder of Sutong Cable-Stayed Bridge.