Structural Control and Health Monitoring

Liu, Cai‐wei; Huang, Xu‐hong; Miao, Ji‐jun; Ba, Guang‐zhong

doi: 10.1002/stc.2350pmid: N/A

To obtain accurate finite element models of reinforced concrete beams for vibrational analyses at elevated temperatures, a multivariate stepwise finite element model (FEM) updating strategy based on a support vector machine is proposed herein. This strategy considers the effects of simultaneous corrections of multiple physical parameters. First, based on the proposed updating strategy, the initial FEM of a simply supported beam was updated with special consideration given to the boundary conditions. Then, vibrational analyses of the simply supported beams at elevated temperatures were carried out through numerical simulations and experiments, and the attenuation response of the modal information was obtained. A comparison between the actual measured structural response and the modified model response shows that the proposed updating method is of practical engineering importance. This study presents a model updating method and the attenuation response of modal information during fire exposure, which lays a foundation for further research on the damage development of a reinforced concrete beam subjected to fire.

Saghafi, Abolfazl; Jazayeri, Sajad; Esmaeili, Sanaz; Tsokos, Chris P.

doi: 10.1002/stc.2354pmid: N/A

A statistical analytical monitoring scheme is developed that utilizes maximum energy of ground‐penetrating radar signals to detect hidden buried objects and estimate their location and depth automatically. The maximum energy is calculated for locations by Welch's power spectral density estimation. Using the proposed analytic, the maximum energy is tightly monitored for a significant change from reference signals generated using target‐free locations. A warning message is triggered when monitoring process detects a site with potential buried objects, on average, 90 cm (2.95 ft) away from the object for 800‐MHz antenna. Continuing the ground‐penetrating radar scan in the same direction and monitoring the signals, the procedure uses a sophisticated hyperbola‐mapping method to estimate the location and depth of buried objects with high accuracy. The analytics could successfully pinpoint the location and depth of hidden objects, respectively, with mean absolute error of 0.38 and 2.03 cm in synthetic noisy environments. Reliable performance of the proposed analytics in real cases that run in real‐time for multiple object detection even in noisy media proves its efficiency for real‐life exploration.

Ying, Zu‐Guang; Ni, Yi‐Qing; Kang, Lei

doi: 10.1002/stc.2351pmid: N/A

Some kinds of structures such as continuous girder viaducts and bridges have periodically spaced supports, and their support damage can potentially be detected using the change in extraordinary dynamic characteristics pertinent to quasiperiodic structure dynamics. In this study, the dynamic characteristics of quasiperiodically multisupported beam structures with local weak coupling are explored by using analytical and numerical methods. The eigenvalue equation and analytical expression of characteristic response of the spaced supported beam are first derived using the Galerkin method. For the periodic beam with four supports in particular, the analytical expressions for calculating natural frequencies and vibration modes are obtained. The fundamental frequency loci veering and local weak coupling between spans of the periodic beam are demonstrated, and the critical value of support stiffness is determined. In the case of quasiperiodic beam with four supports, the frequency loci veering and fundamental modal jump are explicitly illustrated through tuning the support stiffness. The modal jump leads to mode localization around the stiffness‐reduced support, which can be used for determining the support damage. Subsequently, a periodically multisupported girder bridge model in consideration of support damage is addressed, where the stiffness reduction due to support damage induces the period detuning. The natural frequency equation and vibration mode expression of the quasiperiodic girder are elicited. Numerical results illustrate some extraordinary dynamic characteristics including the frequency loci veering and nonlinear reliance of the first natural frequency on support stiffness, the fundamental vibration mode alteration and modal jump, the fundamental mode localization, and noticeable change in absolute mode displacement, which can be used to determine the reduction in support stiffness or damage. The analysis method and results on the dynamic characteristics such as mode localization are greatly helpful for determining the support damage of periodically supported structures and identifying the damage location.

Ivorra, Salvador; Giannoccaro, Nicola Ivan; Foti, Dora

doi: 10.1002/stc.2360pmid: N/A

This paper presents the analysis of the dynamic performances of a simple model related to a squat masonry tower situated in the Swabian Castle of Trani (Italy). The main objective of this paper is to introduce a novel strategy based on a simple model validated by experimental data for defining the influence of the excitation frequency on the structural damping dynamic transmission. To this aim, first, the accelerations have been acquired simultaneously in 23 points of the tower at different levels, both due to environmental vibrations and due to a series of sinusoidal forced vibrations applied at the base by using an electro‐hydraulic shaker device specifically designed for the tests. Four different excitation frequencies have been then selected for exciting the structure. An operational modal analysis has been carried out by the environmental recordings and with the different forcing loads obtaining a very good correlation of the identified frequencies in all the cases. Then a digital filtering process has been applied over all the recorded signals to evaluate the specific contribution for each frequency generated by the shaking device at each level of the tower. Increments of damping ratio have been detected with these forced vibrations at the base. Finally, a simple frame numerical model has been developed to reproduce the dynamic amplification at the most significant locations of the tower. It has been updated not only to have the same main frequencies and modal shapes but also to get a similar response under forced vibrations at the base. A good correlation has been obtained between the model and the real structure for the base forced vibrations at different excitation frequencies in order to correctly predict the dynamic behaviour of the structure.

Jiménez‐Alonso, Javier Fernando; Sáez, Andrés; Caetano, Elsa; Cunha, Álvaro

doi: 10.1002/stc.2356pmid: N/A

In this paper, a biomechanical crowd‐structure interaction model is proposed and calibrated in order to take into account the change of the modal properties of footbridges in lateral direction induced by the pedestrian walking action. The model involves two submodels, namely, (a) the pedestrian‐structure interaction and (b) the crowd submodels. In the first submodel, a single degree of freedom system, which simulates the behaviour of each pedestrian, is projected on the vibration modes of the structure. Herein, the parameters of the first submodel are estimated experimentally from the results of several pedestrian tests conducted on a real footbridge. For the second submodel, the crowd behaviour is modelled via a multiagent method. The performance of the overall model has been assessed successfully via the correlation between the change of the first experimental lateral natural frequency of another footbridge during a pedestrian test and the numerical predictions provided by the proposed model. Therefore, this model becomes a valuable tool to analyse numerically the change of the modal parameters of footbridges due to the pedestrian‐structure interaction.

He, Jingbo; Li, Zuohua; Teng, Jun; Wang, Ying

doi: 10.1002/stc.2348pmid: N/A

The absolute stress of steel members is a key parameter for determining the performance of steel structures. Compared with other nondestructive evaluation methods, ultrasonic methods, which correlate material stress with ultrasonic velocity, have received the greatest amount of research attention. In this study, we investigated the measurement of the absolute stress distribution of steel members using two ultrasonic methods: a longitudinal critically refracted (Lcr) wave method and a shear wave method. The Lcr wave is generated from the longitudinal wave mode conversion and exhibits the greatest sensitivity to stress. The shear waves are generated by the birefringence effect, and their synthesis signal spectrum exhibits a minimum that varies with stress. A comparison of the two absolute stress evaluation methods is performed. Specifically, four steel members with identical dimensions and materials are used to investigate the discreteness of the calibrated parameters. The uniaxial absolute stress distributions of two steel members with variable cross sections are measured using the two methods and verified using the traditional strain gauge method. The results show that the uniaxial stress distributions of the two steel members can be evaluated by both the Lcr wave time‐of‐flight method and the shear‐wave spectrum method, although the latter is more accurate for the measurement of stress distribution. Furthermore, the measurement principles, parametric calibrations, sensitivity, accuracy, and repeatability of the two methods are compared, and their applicability is discussed.

doi: 10.1002/stc.2223pmid: N/A

No abstract is available for this article.

Yang, Yongchao; Sanchez, Lorenzo; Zhang, Huiying; Roeder, Alexander; Bowlan, John; Crochet, Jared; Farrar, Charles; Mascareñas, David

doi: 10.1002/stc.2358pmid: N/A

Cables are critical components for a variety of structures such as stay cables and suspenders of cable‐stayed bridges and suspension bridges. When in operational service, they are vulnerable to cumulative fatigue damage induced by dynamic loads (e.g., the cyclic vehicle loads and wind excitation). To accurately analyze and predict their dynamics behaviors and performance that could be spatially local and temporal transient, it is essential to perform high‐resolution vibration measurements, from which their dynamics properties are identified and, subsequently, a high spatial resolution, full‐modal‐order dynamics model of cable vibration can be established.

Chen, Zhiwei; Yang, Weibiao; Li, Jun; Yi, Tinghua; Wu, Junchao; Wang, Dongdong

doi: 10.1002/stc.2355pmid: N/A

Bridge influence line (BIL) is a promising tool for the real applications in the fields of bridge weight‐in‐motion (BWIM), model updating, damage identification, and load carrying capacity evaluation. The key of such applications is how to obtain the accurate results of BIL. To accurately identify BIL based on bridge dynamic responses induced by a moving vehicle, two critical problems, including how to construct a general representation function of BIL and how to deal with the ill‐posed inverse problem, should be properly resolved. This paper proposes a novel approach based on the adaptive B‐spline basis dictionary and sparse regularization technique for BIL identification. A representation of basis function is first established to construct BIL, and then integrated with a redundant B‐spline basis dictionary to ensure the sparsity of solution. A curvature‐based adaptive node optimization method is proposed to automatically adjust the spatial arrangement of nodes according to the shape of BILs. Numerical and experimental validations are conducted to verify the accuracy and robustness of the proposed approach. The identified BIL results are accurate, indicating that the proposed node‐adaptive optimization and sparse regularization techniques are effective to improve the quality of BIL identification. It is also shown that the proposed approach is not sensitive to the noise interference and configuration of testing vehicle. Through the robustness testing, it is proved that the proposed approach has the merits of high accuracy and strong robustness.

Rana, Shohel; Nagayama, Tomonori; Hisazumi, Kazumasa; Tominaga, Tomonori

doi: 10.1002/stc.2349pmid: N/A

Belt conveyors, widely used in various industries worldwide, are often exposed to corrosive environment. Decades after construction, many of the support structures of belt conveyors have severe degradation, which may cause structural failure and functional stop of associated industries. To ensure the safety and reliability, effective and efficient damage identification of belt conveyor support structures is essential. However, application of existing global vibration‐based damage identification techniques to these structures is difficult due to unavailability of baseline condition, the possible presence of multiple corroded members in a single structure, and the effect of nonstructural components that are occasionally updated. In this paper, a damage identification method of the main members of a belt conveyor support structure is proposed and validated through numerical and experimental studies. Cross‐sectional modes (CSMs), shown to exist on the main member numerically and experimentally, are utilized. Eigenvalue analysis of an FE model of the support structure reveals the characteristics of CSMs and localized CSMs (LCSMs). A damage identification method based on these modes is developed; the existence and location of the damage is evaluated from current state of the structure without the need for before–after comparison. By identifying the distinct LCSMs, multiple damages are also independently identified.