Structural Control and Health Monitoring

doi: 10.1002/stc.1591pmid: N/A

Dorvash, S.; Pakzad, S. N.

doi: 10.1002/stc.1521pmid: N/A

SUMMARY Computational capability of wireless sensor network (WSN) significantly facilitates application of dense sensory arrays, which is increasingly important in health monitoring of large‐scale structural systems. As the wireless sensor technology improves, more complicated tasks can be assigned to sensing units, and the communication between sensing nodes and their base station can be minimized, utilizing in‐network processing. This strategy should be used to address WSN challenges, such as limited communication bandwidth and prohibitive power consumption, associated with wireless communication and battery power. An iterative modal identification algorithm is proposed in this paper, which uses the on‐board processors for estimation of system parameters through iteration cycles. The iterative algorithm was originally developed such that each individual sensor, having an initial estimate of the system parameters, its local measurement, and the excitation signal, updates the estimated model and passes it through the network until convergence. This study further improves the algorithm to eliminate its limitations in need for availability of excitation load and initial estimate of the system parameters. As a result, the algorithm is applicable for modal identification of structural systems under ambient loading without need for prior information about the system parameters. The development of the algorithm is presented in this paper and validated through implementation on a numerically simulated example and a laboratory experiment. Furthermore, its performance is evaluated using data from an ambient vibration test of the Golden Gate Bridge using a WSN. Results of these implementations verify the functionality of the algorithm in monitoring of real‐life structural systems. Copyright © 2012 John Wiley & Sons, Ltd.

Mańka, Michał; Rosiek, Mateusz; Martowicz, Adam; Stepinski, Tadeusz; Uhl, Tadeusz

doi: 10.1002/stc.1523pmid: N/A

ABSTRACT During recent years, an intensive research activity concerning the application of Lamb waves (LWs) for SHM has been observed. LWs may be generated and sensed using different types of transducers, and their selection is essential for the SHM system's performance. Results of the investigation of three types of transducers based on macro‐fiber composite (MFC) are presented in this paper; two types of commercially available MFC actuators are compared with a novel type of custom‐designed interdigital transducer also based on the MFC substrate. After a short presentation of the piezoelectric transducer designed for SHM applications, details concerning the proposed interdigital transducer design are provided. Beampatterns of the investigated transducers are first compared using numerical FEM simulations, and next, the numerically obtained beampatterns are verified experimentally using laser vibrometry. In the final part of this paper, advantages and disadvantages of the investigated transducers are discussed. Copyright © 2012 John Wiley & Sons, Ltd.

Zargar, Hamed; Ryan, Keri L.; Marshall, Justin D.

doi: 10.1002/stc.1525pmid: N/A

SUMMARY Base isolation systems generally perform well under design‐level ground motions to reduce both interstory drift and acceleration demands. During a maximum considered earthquake, however, large displacements in the base level may cause pounding between the structure and perimeter moat wall, which can lead to very high acceleration in the superstructure. A phased passive control device, or ‘gap damper’, has been conceived to control base isolator displacement during extreme events while having no effect on the isolation system performance for earthquakes up to design level. It is by introducing an appropriate initial gap that the device triggers additional energy dissipation during large earthquakes to limit displacements. Various combinations of hysteretic and viscous damping mechanisms are utilized to provide desired additional energy dissipation. A numerical study that assesses the ability of various gap damper models to reduce the base displacement by at least 25% while limiting the acceleration increase at the roof level that results from the sudden engagement of a damping device is devised. The energy dissipation level provided by the damper is optimized to provide the best possible performance. For base isolation systems with effective periods of isolation in the 2.5–3.0 s range, gap damper models incorporating a viscous dashpot are very effective in controlling displacement, whereas gap dampers restricted to a hysteretic damping mechanism are ineffective. The gap damper is less effective for systems with longer periods of isolation (3.5–4.0 s) because the lower target acceleration in this range is more difficult to meet. Copyright © 2012 John Wiley & Sons, Ltd.

Agranovich, G.; Ribakov, Y.

doi: 10.1002/stc.1526pmid: N/A

ABSTRACT Shake tables are widely used for testing structural models subjected to earthquakes. Time histories of real ground motions are reproduced by a moving shake table platform, controlled using an appropriate algorithm, considering the limitations in the platform's maximum displacement. As the real peak ground displacement is usually higher, compared with the platform's stroke, the earthquake records are scaled. Scaling yields distortion in the ground motion spectrum and consequently changes the influence of the earthquake on the tested structure. A method for minimization of the undesired effects, on the basis of linear models of a tested structure, was developed previously. Closeness of power spectral density to response spectra was chosen as the main criterion of scaling efficiency. However, strong earthquakes lead to nonlinear effects in structural response. Supplemental active and passive devices are widely applied for enhancing structural seismic response. Active and semi‐active devices are activated according to structural dynamic behavior, measured during the earthquake. But if the accelerations in the measured feedback include high distortions, control will not be effective as desired. An earthquake record scaling method, proposed in this study, is based on criteria that are more consistent with the tested structure. A mathematical formulation of the problem is developed. Effectiveness of the proposed method is demonstrated by comparing the total earthquake energy and response spectra of real and scaled earthquakes as well as by comparative evaluation of the acceleration distortions of their time histories. Response of two multistory structural models to real and scaled seismic records is compared to demonstrate the proposed method's efficiency, accuracy and convenience. Copyright © 2012 John Wiley & Sons, Ltd.