Abstract
Structural health monitoring (SHM) has been related to damage identification with either operational loads or other environmental loading playing a significant complimentary role in terms of structural safety. In this study, a non-parametric method of time frequency analysis on the measurement is used to address the time-frequency representation for modal parameter estimation and system damage identification of structure. The method employs the
wavelet decomposition of dynamic data by using the modified complex Morlet wavelet with variable central frequency
(MCMW+VCF). Through detail discussion on the selection of model parameter in wavelet analysis, the method is
applied to study the dynamic response of both steel structure and reinforced concrete frame under white noise excitation as well as earthquake excitation from shaking table test. Application of the method to building earthquake response measurement is also examined. It is shown that by using the spectrogram generated from MCMW+VCF method, with
suitable selected model parameter, one can clearly identify the time-varying modal frequency of the reinforced concrete
structure under earthquake excitation. Discussions on the advantages and disadvantages of the method through field
experiments are also presented.
Key Words
damage detection and localization; modified continuous wavelet analysis; Novelty index; seismic response data of building; time-frequency analysis
Address
Wen-Hui Chen: P-Waver Inc., Taipei, Taiwan
Wen Hseuh: Department of Civil Engineering, National Taiwan University, Taipei 10617, Taiwan
Kenneth J. Loh: Department of Structural Engineering, University of California-San Diego, La Jolla, CA 92093, USA
Chin-Hsiung Loh: Department of Civil Engineering, National Taiwan University, Taipei 10617, Taiwan; Department of Structural Engineering, University of California-San Diego, La Jolla, CA 92093, USA
Abstract
In this study, parametric analyses on a hoop-type PZT (lead-zirconate-titanate) interface are performed to estimate the effects of the PZT interface's materials and geometries on sensitivities of impedance responses under strand breakage. The paper provides a guideline for installing the PZT interface suitable in tendon anchorages for damage-sensitive impedance signatures. Firstly, the concept of the PZT interface-based impedance monitoring technique in prestressed tendon anchorage is briefly described. A FE (finite element) analysis is conducted on a multistrands anchorage equipped with a hoop-type PZT interface for analyzing materials and geometric effects. Various material properties, geometric sizes of the interface, and PZT sensor are simulated under two states of prestressing force for acquiring impedance responses. Changes in impedance signals are statistically quantified to analyze the effect of these factors on damage-sensitive impedance monitoring in the tendon anchorage. Finally, experimental analyses are performed to demonstrate the effects of materials and geometrical properties of the PZT interface on damage-sensitive impedance monitoring.
Key Words
damage-sensitive; impedance responses; material and geometric properties; prestressed tendon anchorage; PZT interface
Address
Ngoc-Loi Dang: Urban Infrastructure Faculty, Mien Tay Construction University, Vinh Long 890000, Vietnam
Quang-Quang Pham, Jeong-Tae Kim: Department of Ocean Engineering, Pukyong National University, Nam-gu, Busan 48513, Korea
Abstract
In this paper, an innovative finite element updating method is presented based on the variation wavelet transform coefficients of Auto/cross-correlations function (WTCF). The Quasi-linear sensitivity of the wavelet coefficients of the WTCF concerning the structural parameters is evaluated based on incomplete measured structural responses. The proposed algorithm is used to estimate the structural parameters of truss and plate models. By the solution of the sensitivity equation through the least-squares method, the finite element model of the structure is updated for estimation of the location and severity of structural damages simultaneously. Several damage scenarios have been considered for the studied structure. The parameter estimation results prove the high accuracy of the method considering measurement and mass modeling errors.
Key Words
auto correlation; finite element model updating; sensitivity analysis; structures health monitoring; wavelet transform
Address
Mohsen Sadeghian, Akbar Esfandiari and Manochehr Fadavie: Marine Engineering Department, Amir kabir University of Technology, Tehran, Iran
Abstract
This paper proposes a data-driven methodology for online early damage identification under changing environmental conditions. The proposed method relies on two data analysis methods: feature-based method and hybrid principal component analysis (PCA) and kernel PCA to separate damage from environmental influences. First, spectral sub-band features, namely, spectral sub-band centroids (SSCs) and log spectral sub-band energies (LSSEs), are proposed as damage-sensitive features to extract damage information from measured structural responses. Second, hybrid modeling by integrating PCA and kernel PCA is performed on the spectral sub-band feature matrix for data normalization to extract both linear and nonlinear features for nonlinear procedure monitoring. After feature normalization, suppressing environmental effects, the control charts (Hotelling T2 and SPE statistics) is implemented to novelty detection and distinguish damage in structures. The hybrid PCA-KPCA technique is compared to KPCA by applying support vector machine (SVM) to evaluate the effectiveness of its performance in detecting damage. The proposed method is verified through numerical and full-scale studies (a Bridge Health Monitoring (BHM) Benchmark Problem and a cable-stayed bridge in China). The results demonstrate that the proposed method can detect the structural damage accurately and reduce false alarms by suppressing the effects and interference of environmental variations.
Address
Hossein Babajanian Bisheh: School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran
Gholamreza Ghodrati Amiri: Natural Disasters Prevention Research Center, School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran
Abstract
Lateral vibrations of footbridges may induce synchronization between pedestrians and structure itself, resulting in amplification of such vibrations, a phenomenon identified by lock-in. However, investigations about accelerations and frequencies of the structural movement that are related to the occurrence of synchronization are still incipient. The aim of this paper is to investigate conditions that could lead to avoidance of synchronization among pedestrians themselves and footbridge, expressed in terms of peak acceleration. The focus is on the low acceleration range, employed in some guidelines as a criterion to avoid synchronization. An experimental campaign was carried out, employing a prototype footbridge that was set into oscillatory motion through a pneumatic exciter controlled by a fuzzy system, with controlled frequency and amplitude. Test subjects were then asked to cross the oscillating structure, and accelerations were simultaneously recorded at the structure and at the subject's waist. Pattern and phase differences between these signals were analysed. The results showed that test subjects tended to keep their walking patterns without synchronization induced by the vibration of the structure, for structural peak acceleration values up to 0.18 m/s2, when frequencies of oscillation were around 0.8 to 0.9 Hz. On the other hand, for frequencies of oscillation below 0.7 Hz, structural peak accelerations up to 0.30 m/s2 did not induce synchronization.
Key Words
footbridge; lock-in; pedestrian; synchronization; vibration
Address
Alexandre R. Andrade: Unidade Acadêmica de Controles e Processos Industriais, Instituto Federal da Paraíba, Campus João Pessoa, Av. Primeiro de Maio, 720, João Pessoa 58015-435, Brazil
Roberto L. Pimentel: Departamento de Engenharia Civil e Ambiental, Universidade Federal da Paraíba, Cidade Universitária s/n, João Pessoa 58051-900, Brazil
Simplício A. da Silva, Cícero da R. Souto: Departamento de Engenharia Elétrica, Universidade Federal da Paraíba, Cidade Universitária s/n, João Pessoa 58051-900, Brazil
