Shaking table tests for the experimental verification of the effectiveness of an automated modal parameter monitoring system for existing bridges in seismic areas

Abstract

Reinforced concrete bridges represent a majority of the Italian stock and they play a primary role to ensure the efficiency of the transportation network and prompt rescue in the case of an emergency. However, most of them have been designed and built according to outdated codes, or even without any seismic detailing. The significant impact of strong motions on the road network as well as the human life and economy emphasizes the need for effective strategies for post-earthquake emergency management and to support rescue operations. The present paper aims at evaluating, against real data, the effectiveness of automated modal parameter monitoring for vibration-based Structural Health Monitoring (SHM) of existing bridges in earthquake prone areas. This objective has been pursued in the context of shaking table tests on a 1:3 scale single span bridge representative of existing highway bridges built in the 60's in Italy. The dynamic response of the structure before and after the application of asynchronous seismic input has been analyzed for damage detection and performance assessment. Results show that partially hidden damage can be remotely detected, thus validating the interesting applicative perspectives of automated output-only modal identification and modal-based damage detection for fast assessment of existing bridges in the early earthquake aftershock. The robustness of the SHM system to sensor overload due to earthquake shaking has been also assessed, demonstrating the applicability of modal-based SHM in seismic regions even in the absence of a measurement chain specifically designed to resolve the large amplitude vibrations induced by earthquakes. Finally, the possibility of complementing modal-based SHM with drift-based estimates is explored.

Experiences of Dynamic Identification and Monitoring of Bridges in Serviceability Conditions and after Hazardous Events

“…In the latter configuration, in fact, the natural frequencies remained unaltered after shaking, confirming that no damage occurred. Similar results were obtained by comparing the mode shapes before and after shaking [52]. In the asbuilt configuration, on the contrary, the bridge exhibited clear drops in the natural frequency time series, confirming the occurrence of damage as a result of the applied shaking.…”

“…The latter might yield changes of the modal parameters of the same order of magnitude of the damage-induced variations, thus causing problems of false and/or missed alarms [41]. In the following, the potential of modal-based SHM as a global method for remote damage detection is discussed with reference to a laboratory application [52]. The reliability of modal parameter monitoring in the presence of non-stationary responses due to vehicle-induced excitations is also reviewed.…”

“…It is one of the laboratory activities carried out in the context of the PON 2007-2013 Research Project "STRIT" aimed at detecting earthquake-induced damage at unmeasured locations through the monitoring of the fundamental natural frequencies. More details about the test specimen, designed according to obsolete codes, and data processing procedures can be found in [52]. Brittle failures due to shear and insufficient ductility due to inadequate anchorage detailing or lap splicing, associated to the use of smooth-steel reinforcement bars and low-strength concrete, mark the seismic response of substandard circular piers.…”

Modal parameter identification of structures based on short-time narrow-banded mode decomposition

“…To avoid economic and human losses, early damage detection and reinforcement are vital. In this regard, modal parameter identification (MPI), especially natural frequencies and damping ratios, of civil structures has demonstrated to be critical because these parameters can reflect vibration characteristics (Rainieri et al, 2018). MPI has been extensively applied in damage detection (Magalhães et al, 2012), modal updating (Bagheri et al, 2018), vibration control (Bakule et al, 2016), and seismic design (Muho et al, 2019).…”

Damage Identification in Structural Health Monitoring: A Brief Review from its Implementation to the Use of Data-Driven Applications

“…For instance, methods such as mode shape as damage-detection indicator have been applied to analyze the behavior of a bridge [59]. Other proposals in this kind of structure seek to increase the reliability of operational modal analysis (OMA) concerning external phenomena, such as vibration [60], or the performance of estuaries in seismic areas [61].…”