Analysis of damage identification of self-anchor suspension bridge

Based on a self-anchored suspension bridge with a long span and complex structure, this paper makes a detailed analysis of its stress characteristics before damage and damage characteristics after damage through finite element analysis and bridge load test. Aiming at the main vulnerable components of the main girder, a variety of identification methods based on the existing dynamic damage identification methods are selected for comparative analysis of damage identification, and finally an effective method suitable for bridge girder damage monitoring is determined according to the identification effect of each method. Different damages of main girder, bridge tower and suspender are simulated respectively, and then the static and dynamic damage characteristics of the structure under the same conditions before and after the damage are analyzed with the results of nondestructive analysis of the bridge as reference. The results show that the internal force and deformation caused by the same static and dynamic load and the inherent dynamic characteristics of the structure will change correspondingly when different damages occur to the structure, but the change is small for the moderate damage of 20%. After the suspenders fail completely, the deformation and internal force of the bridge will increase greatly, and the cable force of the adjacent suspenders will increase by 50%.

The damage monitoring and identification of arch bridges provide an important means to ensure the safe operation of arch bridges. At present, many methods have been developed, and the applicability and effectiveness of these methods depend on the damage type, structural configuration and available data. To guide the practical application of these methods, a systematic review is implemented in this paper. Specifically, the damage monitoring and identification methods of arch bridges are divided into the damage monitoring of local diseases and damage identification of overall performance. Firstly, the research on the damage monitoring of the local diseases of arch bridges is reviewed. According to the disease type, it is divided into four categories, including suspender inspection, void monitoring, stress detection and corrosion detection. For each disease, this paper analyzes the principles, advantages and shortcomings of various methods. Then, the damage identification methods of the overall performance of arch bridges are reviewed, including masonry arch bridges, steel arch bridges, reinforced concrete arch bridges and concrete-filled steel tubular arch bridges. And the commonly used damage indexes of damage identification methods are summarized. This review aims to help researchers and practitioners in implementing existing damage detection methods effectively and developing more reliable and practical methods for arch bridges in the future.

Self-anchored cable-stayed suspension bridge has highly competitive in large-span bridge scheme selection due to it combines both stress characteristics and structural characteristics of cable-stayed bridge and self-anchored suspension bridge. This paper focuses on the development of self-anchored and earth-anchored cable-stayed suspension bridge in China, lists the bidding scheme and the actual project of this type bridges.

The global stability of a structure, the stiffness of its main girder and concrete tower, and the variation of the forces of its stay cables are key issues to the safety assessment of an in-service cable-stayed bridge. The efficiency and rationality of local elaborate non-damage-identification could be enhanced by the primary damage identification of cable-stayed bridges on the basis of periodic detection of the cable force and strain monitor in key sections of the main girder. The genetic algorithms of damage identification for cable-stayed bridges were investigated in this paper on the basis of the monitor data of the cable force and strain in a key section of the main girder. A damage detection program for complex civil structure was generated to implement the identification of damage location and extent. The deterioration of the structure was calculated according to the variation of monitor data. It is demonstrated that the results of damage identification from the parametric finite element method are accurate. The method had been verified using a long-span concrete cable-stayed bridge in Ningbo, which has been in use for the past four years.

This paper presents a robust damage identification scheme in which damage is predicted by solving the cross-modal strain energy (CMSE) linear system of equations. This study aims to address the excessive equations issue faced in the assemblage of the CMSE system. A sensitivity index that, to some extent, measures how the actual damage level vector satisfies each CMSE equation, is derived by performing an analysis of the defined residual’s sensitivity to damage. The index can be used to eliminate redundant equations and enhance the robustness of the CMSE system. Moreover, to circumvent a potentially ill-conditioned problem, a previously published iterative Tikhonov regularization method is adopted to solve the CMSE system. Some improvements to this method for determining the iterative regularization parameter and regularization operator are given. The numerical robustness of the proposed damage identification scheme against measurement noise is proved by analyzing a 2-D truss structure. The effects of location and extent of damage on the damage identification results are investigated. Furthermore, the feasibility of the proposed scheme for damage identification is experimentally validated on a beam structure.

Thanks to its sensitive characteristics to damages, modal strain energy (MSE) has been widely utilized for structural damage identification. Various MSE-related techniques on structural damage identification are surveyed and classified as damage index (DI) method, modal strain energy change (MSEC) method, cross-modal strain energy (Cross-MSE) method, and other methods. Four typical MSE-related methods are selected and firstly overviewed. Then damage identification of 1-D beam and 3-D offshore platform structures, considering the issues of spatial incompleteness, noise contamination, etc., are examined systematically with numerical simulation and experimental data. The ability of these four methods to locate damage is compared. Finally, some generalized criteria on these methods for damage identification are concluded, and suggestions for future work are discussed. This brief review aims to help readers identify starting points for research in vibration-based damage identification and health monitoring, and guide researchers and practitioners in better implementing available MSE-based damage identification algorithms.

In this research, a finite element model is established to investigate effective seismic control schemes for a self-anchored suspension bridge (SASB) with three towers. Nonlinear dynamic analyses are conducted to evaluate the seismic performance of SASB with different layout schemes of viscous dampers and buffers, which were installed in longitudinal direction and transversal direction, respectively. The responses of the SASB designed with 10 seismic control schemes are compared to ascertain suitable seismic schemes for SASBs. The results show that the number and location of lateral buffers have an important impact on the dynamic characterization of the SASB, especially for the first lateral mode and lateral fundamental frequency. To effectively increase the seismic performance of SASBs with three towers, mounting buffers between the side towers and the main girder of SASBs is an appropriate scheme. The viscous dampers can effectively decrease the dynamic reaction of the towers and longitudinal deformation of the girder under earthquake excitations. The plan involves the installation of dampers between the main concrete stiffening girder and the side towers as the optimal longitudinal seismic scheme for the SASB. The study offers important insights into the seismic design of SASBs with three towers.

Based on the analytical geometry method, small-plane bending deformation theory and approximate deflection curve equation, a simplified calculation method of section angular displacement will be proposed in this paper, which have been certified by the finite difference method. Then, the influence of number and space of measuring points on the experiment result had been detailed analyzed. Apparently, the method has good precision on premise of sufficient points, which could be an algorithms and experimental norm for beam angular displacement test on bridge loading test and damage identification.

Based on the experimental data from a 1/10 scaled model of the Liede Bridge in Guangzhou, China, the nonlinear behavior of a self-anchored suspension bridge during the process of structural system transformation has been systematically and comprehensively studied. The variation of main cable deformation, hanger tension, and main girder stress during the transformation process is analyzed, and their relationships with the different states of structural system are studied. The characteristics and distribution patterns of the lateral torsional angle of spatial cable clamps are identified. In this paper, the principles of the two stages of construction control for self-anchored suspension bridges are introduced, and construction control targets and error elimination methods for each stage are also discussed. Based on the measured results of an in situ static load test, the response characteristics of main cable axial deformation, hanger tension, and deflection stress of the main girder are described u...

Effective structural model updating and damage identification methods are proposed by using incomplete measured modal data. The exact relationship between the perturbation of structural parameters and the modal properties of the tested dynamic structure is given on the base of dynamic perturbation method. Structural perturbation parameters are properly selected to represent the differences in structural parameters for structural model updating and damage identification at critical point level. Experimental studies for a laboratory tested steel structure model are undertaken to verify the effectiveness of the proposed model updating technique and to investigate the influence of structural damage on changes of modal parameters. Furthermore, a cable-stayed bridge is adopted for numerical investigations on inverse structural damage identification. The results from experimental studies and numerical investigations show the applicability of the proposed method to structural model updating and damage identification. © 2014 Taylor & Francis Group.

Because self-anchored suspension bridge is a floating system, some seismic reduction devices are installed between tower and stiffening girder to re- duce the displacements and forces induced by longitudinal seismic wave. Using time history analysis method, the pounding process of a concrete self-anchored suspension bridge with main span of 180m is studied in detail. The influences of different stiffness, free gap, damping coefficient of the device and different fre- quency spectrum characteristics of seismic wave were considered in the analysis. The parameter analysis reveals that the pounding may increase or decrease the seismic response which is mainly depend on the free gap between the tower and the main girder. The frequency spectrum characteristics of seismic wave have great influence on the displacement, forces and times of pounding. Compared with pounding device, viscous dampers are also researched to reduce the seismic res- ponses of self-anchored suspension bridge and the main influential factors are considered in detail. The conclusions of the study are useful for the practical de- sign of self-anchored suspension.

The structural health status of Hunan Road Bridge during its two-year service period from April 2015 to April 2017 was studied based on monitored data. The Hunan Road Bridge is the widest concrete self-anchored suspension bridge in China at present. Its structural changes and safety were evaluated using the health monitoring data, which included deformations, detailed stresses, and vibration characteristics. The influences of the single and dual effects comprising the ambient temperature changes and concrete shrinkage and creep (S&C) were analyzed based on the measured data. The ANSYS beam finite element model was established and validated by the measured bridge completion state. The comparative analyses of the prediction results of long-term concrete S&C effects were conducted using CEB-FIP 90 and B3 prediction models. The age-adjusted effective modulus method was adopted to simulate the aging behavior of concrete. Prestress relaxation was considered in the stepwise calculation. The results show that the transverse deviations of the towers are noteworthy. The spatial effect of the extra-wide girder is significant, as the compressive stress variations at the girder were uneven along the transverse direction. General increase and decrease in the girder compressive stresses were caused by seasonal ambient warming and cooling, respectively. The temperature gradient effects in the main girder were significant. Comparisons with the measured data showed that more accurate prediction results were obtained with the B3 prediction model, which can consider the concrete material parameters, than with the CEB-FIP 90 model. Significant deflection of the midspan girder in the middle region will be caused by the deviations of the cable anchoring positions at the girder ends and tower tops toward the midspan due to concrete S&C. The increase in the compressive stresses at the top plate and decrease in the stresses at the bottom plate at the middle midspan will be significant. The pre-deviations of the towers toward the sidespan and pre-lift of the midspan girder can reduce the adverse influences of concrete S&C on the structural health of the self-anchored suspension bridge with extra-wide concrete girder.

Self-anchored suspension bridge is a self-balancing system by anchored the main cable at each end of main girder. With complicated configuration and important rule of transferring tension in main cable to main girder, the anchorage region is one of the most critical issues during designing a self-anchored suspension bridge. It is impossible to fully understand the mechanical behavior only by spatial beam and column model but spatial refined model. Because the behavior of anchorage region is greatly influenced by its boundary condition, in this paper, reasonable length of main girder in calculation model is discussed based on the spatial refined model. The mechanical behavior of initial anchorage structure is calculated. A modified anchorage configuration is proposed according to the stresses distribution of anchorage zone. Calculation results show the modified anchorage configuration can make the force transferring smoothly and decrease the stresses of anchorage structure, and it can be referenced to similar bridges.

Development of a software platform for bridge modal and damage identification based on ambient excitation

The detection of damage in bridges subjected to moving loads has attracted increasing attention in the field of structural health monitoring. Processing the dynamic responses induced by moving loads to characterize damage is the key to identifying damage in bridges. On this topic, various methods of processing dynamic responses to moving loads have been developed in recent decades, with respective strengths and weaknesses. These methods appear in different applications and literatures and their features have not been comprehensively surveyed to form a profile of this special area. To address this issue, this study presents a comprehensive survey of methods for identifying damage by processing dynamic responses of cracked bridges subjected to moving loads. First, methods utilizing the Fourier transform to process dynamic responses to moving loads for damage detection in bridges are examined. Second, methods using wavelet transform to process the dynamic responses to moving loads for damage characterization are examined. Third, methods of employing the Hilbert-Huang transform to process the dynamic responses to moving loads for damage identification are examined. Fourth, methods of dynamic response-driven heuristic interrogation of damage in bridges subjected to moving loads are examined. Finally, we recommend future research directions for advancing the development of damage identification relying on processing dynamic responses to moving loads. This study provides a profile of the state-of-the-art and state-of-the-use of damage identification in bridges based on dynamic responses to moving loads, with the primary aim of helping researchers find crucial points for further exploration of theories, methods, and technologies for damage detection in bridges subjected to moving loads.