Narrow Results

The vehicle scanning method (VSM), originally known as the indirect method, is an efficient method for bridge health monitoring that utilizes mainly the responses collected by the moving test vehicles. This method offers the advantage of mobility, efficiency, and cost-effectiveness as it requires only one or a few vibration sensors mounted on the test vehicle, eliminating the need for deployment of numerous sensors on the bridge. Since its initial proposal by Yang and co-workers in 2004, the VSM has gained intensive attention from researchers worldwide. Over the past two decades, significant progress has been made in various aspects of the VSM, including the identification of bridge frequencies, mode shapes, damping ratios, damages, and surface roughness, as well as its application to railways. Previously, some review papers and the book Vehicle Scanning Method for Bridges were published on the subject. However, research on the subject continues to boom at a speed that cannot be adequately by existing review papers or book, as judged by the fast-increasing number of relevant publications. In order to provide researchers with an overall understanding of the up-to-date researches on the VSM, a state-of-the-art review of the related research conducted worldwide is compiled in this paper. Comments and recommendations will be provided at appropriate points, and concluding remarks, including future research directions, will be presented at the end of the paper.

To determine its actual dynamic responses under the wind loads, modal identification from the field tests was carried out for the Kao Ping Hsi cable-stayed bridge in southern Taiwan. The dynamic characteristics of the bridge identified by a continuous wavelet transform algorithm are compared with those obtained by the finite element analysis. The finite element model was then modified and refined based on the field test results. The results obtained from the updated finite element model were shown to agree well with the field identified results for the first few modes in the vertical, transverse, and torsional directions. This has the indication that a rational finite element model has been established for the bridge. With the refined finite element model, a nonlinear analysis in time domain is employed to determine the buffeting response of the bridge. Through validation of the results against those obtained by the frequency domain approach, it is confirmed that the time domain approach adopted herein is applicable for the buffeting analysis of cable-stayed bridges.

This paper presents an improved method called the consistent multilevel random decrement technique in conjunction with eigensystem realization algorithm (RDT-ERA) for modal parameter identification of linear dynamic systems using the ambient vibration data. The conventional RDT-ERA is briefly revisited first and the problem of triggering level selection in the RDT is thoroughly studied. Due to the use of a single triggering level by the conventional RDT-ERA, an inappropriate triggering level may produce poor random decrement (RD) functions, thereby yielding a poor estimate of modal parameters. In the proposed consistent multilevel RDT-ERA, multiple triggering levels are used and a consistency analysis is proposed to sift out the RD functions that deviate largely from the majority of the RD functions. Then the ERA is applied to the retained RD functions for modal parameter identification. Subsequently, a similar consistency analysis is conducted on the identified modal parameters to sift out the outliers. Finally, the final estimates of the modal parameters are calculated using weighted averaging with the weights set proportional to the number of RD segments extracted from the corresponding triggering levels. The proposed method is featured by the fact that the information from the signal is fully utilized using multiple triggering levels and the outliers are sifted out using consistency analysis, thus making the identified result more accurate and reliable. The effectiveness and accuracy of the method have been demonstrated in the examples using the simulated data and experimental data.

In 2004, Yang and co-workers proposed the extraction of bridge frequencies from the dynamic response of a moving test vehicle [Y. B. Yang, C. W. Lin and J. D. Yau, Extracting bridge frequencies from the dynamic response of a passing vehicle, J. Sound Vib.272 (2004) 471–493] and verified the technique by a field test [C. W. Lin and Y. B. Yang, Use of a passing vehicle to scan the bridge frequencies — An experimental verification, Eng. Struct.27(13) (2005) 1865–1878]. This technique was extended to construction of mode shapes [Y. B. Yang, Y. C. Li and K. C. Chang, Constructing the mode shapes of a bridge from a passing vehicles: A theoretical study, Smart Struct. Syst.13(5) (2014) 797–819] and damage identification of bridges. It was referred to as the indirect method for bridge measurement because no vibration sensors are needed for installation on the bridge, but it only requires one or few vibration sensors on the test vehicle. When compared with the conventional direct method that relies fully on the response of the bridge fitted with vibration sensors, the advantage of the indirect method is clear: mobility, economy, and efficiency. Over the past years, many research studies were conducted along the lines of the indirect method for bridge measurement. Significant advances have been made on various aspects of application. This paper represents a state-of-the-art review of the related research works conducted worldwide. Comments and recommendations will be made at proper places, while concluding remarks including future research directions will be presented at the end of the paper.

The vehicle scanning method (VSM), an indirect approach for bridge measurement, has attracted intensive attention since it was proposed. By this method, a moving test vehicle is employed to detect the “mechanical” properties of the bridge, e.g. frequencies, mode shapes, damages, etc., utilizing the interaction between the two substructures. Compared with the conventional direct approach that requires quite a few sensors and data loggers to be fitted on the bridge, the advantage of the VSM is obvious: mobility, economy, and efficiency. As for railways, the broader vehicle-based techniques have long been used to detect the “geometrical” properties of the track, such as track profiles and rail conditions. Relatively little use has been made of the interaction between the moving vehicle/train and the track/bridge. This paper is a state-of-the-art report of the VSM’s applications to highway bridges and the vehicle-based techniques to railway tracks. It starts with a summary of the pioneering works by Yang and co-workers on the VSM. Then, the applications of the techniques to highway bridges and railway tracks will be separately reviewed. Conclusions will be made, along with future research directions, at the end of the paper.

For high-rise buildings subjected to ambient excitations such as typhoons and earthquake actions, their structural responses may include non-stationary features. Under such conditions, traditional modal identification methods may not be applicable due to the violation of the stationary assumption of the response signals. To deal with this issue, a novel modal identification method is presented in this paper based on combination of the variational mode decomposition (VMD) and direct interpolation (DI) techniques. Through numerical simulation study of a three-story frame structure, the effectiveness and accuracy of the combined VMD-DI method for modal identification of the structure are validated for the case of the structural responses containing non-stationary properties and high-level noise. Moreover, the novel method is further applied to the field measurements of acceleration responses of a 600m high skyscraper during a typhoon. The identified results verify the applicability and accuracy of the combined VMD-DI method in field measurements. This paper aims to provide an effective tool for modal identification from non-stationary structural responses of high-rise buildings.

Power spectrum density transmissibility (PSDT) functions have attracted widespread attention in operational modal analysis (OMA) because of their robustness to excitations. However, the selection of the peaks and stability axes are still subjective and requires further investigation. To this end, this study took advantage of PSDT functions and support-vector machines (SVMs) to propose a two-stage automated modal identification method. In the first stage, the automated identification of peaks is achieved by introducing the peak slope (PS) as a critical index and determining its threshold using the SVM classifier. In the second stage, the automated identification of the stability axis is achieved by introducing the relative difference coefficients (RDCs) of the modal parameters as indicators and determining their thresholds using the SVM classifier. To verify its feasibility and accuracy, the proposed method was applied to an ASCE-benchmark structure in the laboratory and in a high-rise building installed with a structural health monitoring system (SHMS). The results showed that the automated identification method could effectively eliminate spurious modes and accurately identify the closely spaced modes. The proposed method can be automatically applied without manual intervention, and it is robust to noise. It is promising for application to the real-time condition evaluation of civil structures installed with SHMSs.

The vehicle scanning method (VSM), an indirect approach for bridge measurement, has attracted intensive attention since it was proposed by Yang and co-workers in 2004. This method is featured by the fact that no vibration sensors need to be mounted on the bridge, but only one or few vibration sensors are required on the test vehicle. Such an idea has been verified by the field tests, and then quickly extended to construction of mode shapes, identification of damping ratios, and detection of damages for bridges, among others. Compared with the conventional direct method that relies fully on the vibration responses recorded by sensors equipped on the bridge, the advantage of the indirect method is obvious: mobility, economy, and efficiency. Over the years, a rapidly growing number of research works have been conducted along the lines of the VSM for bridge measurement. Particularly, extensive lab experiments and field tests have been carried out worldwide to implement the VSM, resulting in numerous new findings. Moreover, while the technique is still flourishing, it is nourished by inclusion of modern devices such as smartphones, vehicular networks, and cloud. In 2018, a review paper was compiled by two of the authors. To reflect the recent rapid growth of research in this area since then, there exists a need to make an expansion to include the huge number of newly published papers (274 papers in total). As an extension of the 2018 paper, this paper represents a state-of-the-art review of the related researches conducted worldwide. Comments and recommendations will be made at proper places, while concluding remarks including future research directions will be presented at the end of the paper.

For high-rise buildings subjected to typhoon or earthquake actions, the excitations are likely non-stationary, which inevitably violates the stationary assumption that is generally adopted by conventional modal identification methods. Under such a condition, conventional modal identification methods may not be applicable, and their performances need to be evaluated. To this end, the performances of seven widely used modal identification algorithms for structural modal estimation under non-stationary excitations are evaluated via a numerical simulation study. Then, three methods with good performance are selected to evaluate their applicability and accuracy for field measurements involving non-stationary excitations. From the comparative study, a time–frequency domain method with the best performance among these seven methods is employed to investigate the structural dynamic properties of a 509-m-tall skyscraper under typhoon and earthquake excitations. Based on the reliable modal estimates, the relationships between the modal properties with response amplitude and environmental temperature are presented and discussed. This paper aims to identify the effective methods for accurate estimation of structural modal parameters based on non-stationary structural responses and investigate the structural dynamic properties of high-rise buildings under typhoon and earthquake excitations.

The structural dynamic response reconstruction of large-scale civil engineering structures using traditional methods results in heavy computational burden with low efficiency. To improve efficiency, a novel time-domain response reconstruction method based on model condensation and modal decomposition is proposed in this paper. The finite element model of the target structure is transformed and condensed. The system matrices of the condensed model have lower dimensionality than those of the original finite element model. A checking procedure based on the modal assurance criterion is developed to ensure the accuracy of the condensed system. Measured dynamic responses are decomposed to time-domain modal responses at measured degrees of freedom (DOFs) using band-pass filters. The mode shape matrix of the condensed model is used to calculate the modal responses at the unmeasured DOFs. Following modal superposition and coordinate transformation, the dynamic responses at unmeasured DOFs are reconstructed without knowledge of the excitation. The accuracy and efficiency of the proposed methodology are verified in a numerical case study of a three-dimensional building frame model and an experimental case study of a two-story steel frame under laboratory conditions. In contrast with the numerical case study, the effects of modeling error and measurement noise are considered in the experiment verification. The results show the outstanding performance of the proposed methodology when compared with a traditional response reconstruction method.

Nonlinear behavior is present in the operating conditions of many mechanical systems, especially if nonsmall oscillations are considered. In these cases, in order to improve vibration control performance, a common engineering practice is to design the control system on a set of linearized models, for given operating conditions. The well-known gain-scheduling technique allows the parameters of the control law to be changed according to the current working condition, also increasing system stability. However, more recently new control logics directly applicable to the systems in nonlinear form have been developed. The aim of this paper is to study, both numerically and experimentally, the dynamic of a mechanical system (a 3-link flexible manipulator) comparing the performance of a fully nonlinear control (the sliding-mode control) and a standard linearized approach.

In this paper, the dynamic interaction of human body and structure is studied The shaking table experiment with a person standing on a rigid table supported by springs is firstly carried out to determine the dynamic characteristics of the coupled system. It is shown that the body mainly contributes only one degree of freedom to the human-structure coupled system. Then, the two-degree-of-freedom (TDOF) coupled model of the human-structure system is developed through the energy variation by considering the standing human body as an elastic bar of two segments with distributed mass, stiffness and damping. Based on the experiment data, the dynamic parameters of the TDOF coupled system are determined by using the least square method (LSM). The mechanical parameters such as the damping ratio and the distributions of mass and stiffness of the human body model of two segments are identified by adopting the inversing technique Finally, the determined body model is applied to analyze the free vibration of beams and plates occupied by standing persons. The governing differential equations of the human-beam system and the human-plate system are, respectively, derived out. The dynamic characteristics of the human-structure interaction are obtained by the use of the complex mode theory. The results are compared with the experimental ones and those from the finite element simulations. Good agreement is observed for all cases.