Structural Control and Health Monitoring

Wei, Bowen; Yuan, Dongyang; Xu, Zhenkai; Li, Lianghui

doi: 10.1002/stc.2188pmid: N/A

Dam deformation is double effected by the internal and external environments, showing high nonlinear characteristics. Information mining of dam prototype observation data and effective components contained in the residual sequence is limited in conventional dam deformation forecast models. In order to fully explore the complex nonlinear relationship between dam deformation and environmental factors, modified hybrid forecast model considering chaotic residual errors is proposed on the combination of shuffled frog leapfrog algorithm and chaos theory in this study. Hybrid models are established on the basis of dam deformation prototype observation data, and modified hybrid forecast model is established by determining the optimal weight of each hybrid model with shuffled frog leapfrog algorithm. Considering the chaotic characteristics contained in the residual sequence of modified hybrid forecast model, residual sequence is analyzed and forecasted by chaos theory. By superimposing the residual forecast value with the forecast value of modified hybrid forecast model, modified hybrid forecast model considering chaotic residual errors is established. Example shows that, compared with conventional models, the proposed model is better in fitting precision and convergence speed, and forecast capability is significantly improved by considering the effective components contained in the residual sequence, which presents a new method of the deformation forecast for other hydraulic structures.

Caddemi, S.; Caliò, I.; Cannizzaro, F.; Morassi, A.

doi: 10.1002/stc.2194pmid: N/A

In this work, a model of the Euler–Bernoulli beam in presence of multiple‐concentrated open cracks, based on the adoption of a localized flexibility model, is adopted. The closed‐form solution in terms of transversal displacements due to static loads and general boundary condition is exploited to propose an inverse damage identification procedure. The proposed identification procedure does not require any solution algorithm, on the contrary is formulated by means of simple explicit sequential expressions for the crack positions and intensities including the identification of the integration constants. The number of possible detected cracks depends on the couples of adopted sensors. Undamaged beam zones can also be easily detected in relation to the sensor positions. The analytical character of the explicit expressions of the identification procedure makes the inverse formulation applicable to damaged beams included in more complex frame structures.

Li, Dongsheng; Tan, Meiling; Zhang, Shuaifang; Ou, Jinping

doi: 10.1002/stc.2189pmid: N/A

Stress corrosion is a major failure type of prestressed steel strands damage. Currently, no effective monitoring method exists. This paper is an analysis of the acoustic emission (AE) characteristic signal from the stress corrosion damage to prestressed steel strands using the ant colony optimization and self‐organizing feature mapping. First, AE characteristic signals at the different stages of the stress corrosion were obtained through the stress corrosion experiments on prestressed steel strands, which can primarily present the corrosion mechanism and different corrosion sources. Subsequently, the ant colony optimization was applied to analyze the AE characteristic signals of stress corrosion. This resulted in the identification of the four main types of AE sources of stress corrosion on prestressed steel strands. The AE ant colony optimization cluster analysis, based on the principal component analysis technology, can separate the four types of damage sources totally and judge the evolution process of corrosion damage and broken wires signal easily. Finally, the self‐organizing feature mapping neural network technology applied to the pattern recognition of stress corrosion on prestressed steel strands. The AE characteristic parameter distribution of different clusters can be realized.

Narazaki, Yasutaka; Hoskere, Vedhus; Spencer, Billie F.

doi: 10.1002/stc.2207pmid: N/A

Free vibration measurements provide useful information in performing modal identification of civil infrastructure. Free vibration tests have been carried out frequently, because of the simple implementation and the availability of well‐established pre/postprocessing techniques. In particular, the eigensystem realization algorithm (ERA) can be used with free vibration data to extract modal information in a straightforward and automatic manner. However, using free vibration data with the ERA is often problematic for civil infrastructure, because of the significant noise in the measurements caused primarily by small vibration amplitudes and higher structural damping. To address this problem, a method for generating ERA input is proposed that reduces the effect of noise in measured free vibration data. The proposed method is an extension of the natural excitation technique developed for stationary random vibration signals. The natural excitation technique method is adjusted to accommodate free vibration data by replacing the cross‐correlations of stationary random processes with the temporal cross‐correlations of free vibration signals. Then, an approach to reduce the noise effect in the temporal cross‐correlations is proposed based on linear superposition of the cross power spectrum densities of overlapping data segments. Finally, results of the ERA using the proposed approach are compared with the corresponding results from directly applying ERA to the free vibration data. The comparisons using numerical and field test data show that the proposed method outperforms the conventional approach, especially for the modes whose amplitudes are small in the measured free vibration signals.

Acikgoz, Sinan; DeJong, Matthew J.; Soga, Kenichi

doi: 10.1002/stc.2187pmid: N/A

Dynamic displacement measurements provide useful information for the assessment of masonry rail bridges, which constitute a significant part of the bridge stock in the United Kingdom and Europe. Commercial 2D digital image correlation (DIC) techniques are well suited for this purpose. These systems provide precise noncontact displacement measurements simultaneously at many locations of the bridge with an easily configured camera set‐up. However, various sources of errors can affect the resolution, repeatability, and accuracy of DIC field measurements. Typically, these errors are application specific and are not automatically corrected by commercial software. To address this limitation, this paper presents a survey of relevant DIC errors and discusses methods to minimise the influence of these errors during equipment set‐up and data processing. A case study application of DIC for multipoint displacement measurement of a masonry viaduct in Leeds is then described, where potential errors due to lighting changes, image texture, and camera movements are minimised with an appropriate set‐up. Pixel‐metric scaling errors are kept to a minimum with the use of a calibration method, which utilises vanishing points in the image. However, comparisons of DIC relative displacement measurements to complementary strain measurements from the bridge demonstrate that other errors may have significant influence on the DIC measurement accuracy. Therefore, the influence of measurement errors due to lens radial distortion and out‐of‐plane movements is quantified theoretically with pinhole camera and division distortion models. A method to correct for errors due to potential out‐of‐plane movements is then proposed.

doi: 10.1002/stc.2098pmid: N/A

No abstract is available for this article.

Saraygord Afshari, S.; Pourtakdoust, Seid H.

doi: 10.1002/stc.2199pmid: N/A

The utility of probability density evolution method for reliability‐based active vibration control of a cantilevered flexible beam is experimentally investigated. In this respect, an optimal linear quadratic regulator (LQR) is utilized together with an observer to design an online full‐state feedback controller. In order to design a well‐performing controller and to simulate the controller performance, a system model is obtained via identification techniques. Reliability tests are consequently performed to verify the effectiveness of the presented reliability assessment method as a foundation for reliability‐based control. Subsequently, a hybrid metaheuristic optimization scheme of continuous ant colony system is used for simultaneous integrated tuning of the LQR and observer parameters through all processes. Optimization of the controller and the observer is performed with the objective of system structural reliability. An optimized version of classical LQR controller is also developed for making comparisons between the two control methods. Finally, a comparison is made between the mean power consumption of the 2 controllers. It is realized that the reliability‐based controller decreases operating costs without compromising system safety.

Tong, Xin; Zhao, Xiaowei

doi: 10.1002/stc.2204pmid: N/A

We investigate the optimization of multiple tuned mass dampers (TMDs) to reduce vibrations of flexible structures described by partial differential equations, using the nonuniform Spacecraft Control Laboratory Experiment (NASA SCOLE) beam system with multiple dominant modes as an illustrative application. We use multiple groups of TMDs with each group being placed at the antinode of the mode shape of a dominant mode of the SCOLE beam. We consider both the harmonic and random excitations, for which we employ frequency‐limited H∞ and H2 optimizations respectively to determine the parameters of the TMDs. Our optimization scheme takes into account the trade‐off between effectiveness and robustness of the multiple TMDs to suppress the multiple dominant modes of the SCOLE beam. Simulation studies show that our scheme achieves substantial improvements over the traditional methods in terms of both effectiveness and robustness and that with equal total mass, TMD systems with each group having multiple TMDs are more effective and more robust than the ones with each group having a single TMD.

Yue, Hongyuan; Chen, Jianyun; Xu, Qiang

doi: 10.1002/stc.2184pmid: N/A

It is of great significance to conduct seismic qualification and mitigation for composite bushing, whose damage may cause massive power outage and huge cost of repair. In this paper, the annular tuned liquid damper (ATLD), utilizing the sloshing characteristics of transformer oil in the dome, is proposed to reduce the seismic responses of the composite bushing. As to the annular feature of the metallic dome, the simplified formulas for calculating the liquid sloshing frequencies in the dome are derived based on the linear wave theory, which provides a direct and fast way for the predesign of ATLD. Comparing with the experimental results reported in literature, the accuracy and applicability of the proposed formulas are verified. In addition, parametric studies of the first 3 sloshing frequencies including liquid height and the outer and the inner radii are carried out. The optimal tuning analysis of vibration reduction in frequency domain is performed on the structure base excitation. The vibration reduction analyses in time domain of the ATLD for the composite bushing subjected to real earthquake records are carried out and discussed simultaneously. It is shown that the simplified formulas presented in this paper provide a convenience for the predesign of ATLD and the optimal ATLD is effective in reducing the vibration of the composite bushing.

Yang, Yongchao; Dorn, Charles; Mancini, Tyler; Talken, Zachary; Kenyon, Garrett; Farrar, Charles; Mascareñas, David

doi: 10.1002/stc.2193pmid: N/A

Structures with complex geometries, material properties, and boundary conditions exhibit spatially local dynamic behaviors. A high‐spatial‐resolution model of the structure is thus required for high‐fidelity analysis, assessment, and prediction of the dynamic phenomena of the structure. The traditional approach is to build a highly refined finite element computer model for simulating and analyzing the structural dynamic phenomena based on detailed knowledge and explicit modeling of the structural physics such as geometries, materials properties, and boundary conditions. These physics information of the structure may not be available or accurately modeled in many cases, however. In addition, the simulation on the high‐spatial‐resolution structural model, with a massive number of degrees of freedom and system parameters, is computationally demanding. This study, on a proof‐of‐principle basis, proposes a novel alternative approach for spatiotemporal video‐domain high‐fidelity simulation and realistic visualization of full‐field structural dynamics by an innovative combination of the fundamentals of structural dynamic modeling and the advanced video motion manipulation techniques. Specifically, a low‐modal‐dimensional yet high‐spatial (pixel)‐resolution (as many spatial points as the pixel number on the structure in the video frame) modal model is established in the spatiotemporal video domain with full‐field modal parameters first estimated from line‐of‐sight video measurements of the operating structure. Then in order to simulate new dynamic response of the structure subject to a new force, the force is projected onto each modal domain, and the modal response is computed by solving each individual single‐degree‐of‐freedom system in the modal domain. The simulated modal responses are then synthesized by the full‐field mode shapes using modal superposition to obtain the simulated full‐field structural dynamic response. Finally, the simulated structural dynamic response is embedded into the original video, replacing the original motion of the video, thus generating a new photo‐realistic, physically accurate video that enables a realistic, high‐fidelity visualization/animation of the simulated full‐field vibration of the structure. Laboratory experiments are conducted to validate the proposed method, and the error sources and limitations in practical implementations are also discussed. Compared with high‐fidelity finite element computer model simulations of structural dynamics, the video‐based simulation method removes the need to explicitly model the structure's physics. In addition, the photo‐realistic, physically accurate simulated video provides a realistic visualization/animation of the full‐field structural dynamic response, which was not traditionally available. These features of the proposed method should enable a new alternative to the traditional computer‐aided finite element model simulation for high‐fidelity simulating and realistically visualizing full‐field structural dynamics in a relatively efficient and user‐friendly manner.