Yonghui An

A Test Method for Damage Diagnosis of Suspension Bridge Suspender Cables

This article proposes a model-free test method for damage diagnosis of suspender cables because these cables are one of the most vulnerable components of the bridge. Many previous damage detection methods require an accurate finite element model but this method includes two procedures: the mean normalized curvature difference procedure and the curvature difference probability procedure. The test method does not eliminate the need for manual inspection, but changes it from observation to a more quantified method. Numerical results for single and multiple damage cases indicate that: (1) both procedures can be effective for damage diagnosis of suspender cables; (2) small damage can be more easily diagnosed in long suspender cables than short ones; and (3) noise is generally not a problem because the signal-to-noise ratio can be improved by increasing the pulse excitation magnitude for a suspender cable. The potential of the method for practical applications is increased with these points.

Experimental and numerical studies on damage localization of simply supported beams based on curvature difference probability method of waveform fractal dimension

Accurate structural damage localization in engineering is still a challenge due to high noise and low accuracy of the structural finite element model. With the most basic type of construction, the simply supported beam is the most widely used type of structures in short and medium span bridges. Therefore, it is imperative to study their damage detection methods, which can be used in engineering. To solve this problem, an alternative method for damage detection is proposed in this study on the basis of fractal theory and curvature mode shapes method: the curvature difference probability method of waveform fractal dimension. The influence of different amplitudes of excitation on results and the robustness against noise are also discussed. Based on a simply supported beam model in the laboratory, both the experimental and numerical results using the technique under step or pulse excitation indicate that the proposed method can be used in damage localization very well, and it exhibits high-noise insusceptibility: it is still feasible even if the noise level is up to 15%, which lays a good foundation for engineering application. Moreover, the proposed technology needs no finite element model of the detected structures. Therefore, it is quite simple in the procedure.

Dempster–Shafer evidence theory approach to structural damage detection

In this study, the Dempster–Shafer (D–S) evidence theory-based approach for structural damage detection is presented. First, the damage basic probability assignment (BPA) function of substructures using each data set measured from the monitored structure is calculated. Then, the D–S evidence theory is employed to combine the individual damage BPAs in order to reach the final damage detection results. To reduce the computational cost of this method when used in complex structures, the preliminary damage range is first localized by modal strain energy method. An experimental investigation on a 20-bay rigid truss structure is carried out to illustrate the identified ability of the proposed approach with considering the uncertainty of model and measurement noise. The results indicate that the damage detection results obtained by combining the damage BPAs from each test data are better than the individual results obtained by each test data separately.

An algorithm for damage localization in steel truss structures: Numerical simulation and experimental validation

It is imperative to study the damage detection methods of steel truss structures that are always employed in extreme environment. Accurate structural damage localization is still a challenge due to high noise and low accuracy of the structural finite element model. To develop a dependable damage localization technique for truss structural health monitoring, a novel idea of damage localization is proposed: the curvature difference method of strain waveform fractal dimension, based on fractal theory and curvature method. To validate the approach, a simply supported bailey steel truss benchmark model has been designed and constructed in the laboratory. Based on the model, both experimental and numerical simulation results using the procedure under pulse excitation indicate that it is feasible and effective to detect the change of boundary conditions and the stiffness reduction of a truss member. In addition, the proposed technique exhibits high-noise insusceptibility (e.g. it works for noise levels up to 20% for a 10% truss member stiffness reduction). Moreover, the proposed technology is robust against the accuracy of the finite element model of measured structures, which decrease the workload of model updating dramatically. All these lay a good foundation for its engineering application.

Transverse Dynamic Mechanical Behavior of Hangers in the Rigid Tied-Arch Bridge under Train Loads

The rigid hanger is one of the main load-bearing components in a rigid tied-arch bridge that is common used in high-speed railway lines, and the mechanism for influences of train loads on the hangers’ transverse vibration -still requires clarification. This paper investigates the transverse vibration of rigid hangers in the rigid tied-arch bridge under train loads from three foci. Firstly, the accurate finite-element model of a rigid tied-arch bridge and the sub-model of each hanger of this bridge are established. The dynamic characteristics analysis of the whole bridge and each hanger are presented. Secondly, because the resonance theory used for stay cables and main girder cannot be used for rigid hangers in arch bridges, the hanger’s transverse vibration formula with consideration of the interaction of rigid hangers and main girder is proposed based on the classic structural dynamics. Thirdly, a simplified load model that can reflect the mechanical characteristics of high-speed rail Electric Multiple Units is established. The transverse dynamic displacements of hangers and their dynamic amplification factors in 6 field load cases are presented by nonlinear dynamic analysis; and also they have been validated based on the data from the structural health monitoring system. The conclusions show that generally the resonance between hangers and main girder is unlikely to happen in a rigid tied-arch bridge and the transverse dynamic displacement at long rigid hangers and the dynamic amplification factors of transverse dynamic displacements at short rigid hangers are required to be paid more attention; moreover, the parameters that affect the transverse vibration of hangers have been determined; finally, the geometry, cross sectional form, the spatial location of hangers and train speed can affect the transverse dynamic mechanical behavior of hangers. This work also gives a suggestion which lays a foundation for the better design, maintenance and long-term monitoring of hangers in a long-span rigid tied-arch bridge.

Axial Strain Accelerations Approach for Damage Localization in Statically Determinate Truss Structures

This work proposes an efficient and reliable method for damage localization in truss structures. The damage is localized on the basis of measured acceleration signals of the structure followed by simple statistical signal processing. It has three main advantages over many existing methods. First, it can be directly applied to real engineering structures without the need of identifying modal parameters or solving any global optimization problem. Second, the proposed method has higher sensitivity to damage than some other frequently used methods and allows to localize damage as small as a few percentages. Third, it is a model-free method, which does not require precise finite element model development or updating. Validation of the method has been conducted on numerical examples and laboratory-scale trusses. Two types of frequently used trusses have been selected for this study, namely, Howe and Bailey trusses. The presented experimental validation of the method shows its efficiency and robustness for damage localization in truss structures.

Experimental and numerical studies on a test method for damage diagnosis of stay cables

To diagnose the state of stay cables, a vibration-based model-free damage diagnosis method of stay cables using the changes in natural frequencies is further proposed and validated. The structural frequency is rapidly and easily acquired; moreover, it is simple and reliable for damage diagnosis. The frequency would change after the stay cable is damaged, so the frequency change could be used as the damage index. However, the stay cables are very long in long-span cable-stayed bridges, and their frequencies are very small; the frequency change due to small damage of the stay cable would be submerged by the surrounding noise and error of parameter identification process. A temporary diagonal steel bar–based method is used to solve this issue. The steel bar is installed with one end on the stay cable close to the bottom anchor head and the other end on the bridge deck; thus, the stay cable is divided into a short part and a long part by the steel bar. The frequency of a stay cable with a given tension force increases with the decrease in its length; according to the qualitative analysis, the frequency of the short part increases dramatically, and the local frequency change of the short part due to the same damage in the whole stay cable is amplified dramatically; thus, the small damage of a stay cable can be diagnosed easily. Numerical simulations of a stay cable selected from a cable-stayed bridge and a laboratorial stay cable are used to validate the method and also give a recommended rule for design of the temporary diagonal steel bar; experimental validation has also been conducted. All the results indicate that the proposed method works very well in damage diagnosis of stay cables. The proposed method is an output-only, model-free, fast and economical damage diagnosis method for stay cables.

Fast Warning Method for Rigid Hangers in a High-Speed Railway Arch Bridge Using Long-Term Monitoring Data

AbstractExcessive vibration of arch bridge hangers is a potential threat to the driving safety of high-speed trains; therefore, it is important to study the vibration characteristics and fast warni...