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CONTENTS
Volume 4, Number 4, December 2017
 

Abstract
Impedance-based damage detection method has been known as an innovative tool with various successful implementations for structural health monitoring of civil structures. To monitor the local critical area of a structure, the impedance-based method utilizes the high-frequency impedance responses sensed by piezoelectric sensors as the local dynamic features. In this paper, current advances and future challenges of the impedance-based structural health monitoring are presented. Firstly, theoretical background of the impedance-based method is outlined. Next, an overview is given to recent advances in the wireless impedance sensor nodes, the interfacial impedance sensing devices, and the temperature-effect compensation algorithms. Various research works on these topics are reviewed to share up-to-date information on research activities and implementations of the impedance-based technique. Finally, future research challenges of the technique are discussed including the applicability of wireless sensing technology, the predetermination of effective frequency bands, the sensing region of impedance responses, the robust compensation of noise and temperature effects, the quantification of damage severity, and long-term durability of sensors.

Key Words
impedance responses; wireless impedance sensor; PZT interface; temperature effect; damage detection; structural health monitoring

Address
Thanh-Canh Huynh, Ngoc-Loi Dang and Jeong-Tae Kim:Department of Ocean Engineering, Pukyong National University, 599-1 Daeyon-3dong, Nam-gu, Busan 608-737, Republic of Korea


Abstract
Based on the alternative stabilization diagram by varying the time lag parameter in the stochastic subspace identification analysis, this study aims to investigate the measurements from several cases of civil structures for extending the applicability of a recently noticed criterion to ensure stable identification results. Such a criterion demands the time lag parameter to be no less than a critical threshold determined by the ratio of the sampling rate to the fundamental system frequency and is firstly validated for its applications with single measurements from stay cables, bridge decks, and buildings. As for multiple measurements, it is found that the predicted threshold works well for the cases of stay cables and buildings, but makes an evident overestimation for the case of bridge decks. This discrepancy is further explained by the fact that the deck vibrations are induced by multiple excitations independently coming from the passing traffic. The cable vibration signals covering the sensor locations close to both the deck and pylon ends of a cable-stayed bridge provide convincing evidences to testify this important discovery.

Key Words
alternative stabilization diagram; stochastic subspace identification; civil structure; time lag parameter; multiple excitations

Address
Wen-Hwa Wu, Chien-Chou Chen and Gwolong Lai: Department of Construction Engineering, National Yunlin University of Science and Technology,123 University Road, Douliu, Yunlin 640, Taiwan
Sheng-Wei Wang: Intelligent Electronic Systems Division, National Chip Implementation Center, National Applied Research Laboratories, Hsinchu City 300, Taiwan



Abstract
In this study effects of various parameters like a number of bays, the stiffness of the structure along with the height of the structure was examined. The fundamental period of vibration T of the building is an important parameter for evaluation of seismic base shear. Empirical equations which are given in the Indian seismic code for the calculation of the fundamental period of a framed structure, primarily as a function of height, and do not consider the effect of number of bays and stiffness of the structure. Building periods predicted by these expressions are widely used in practice, although it has been observed that there is scope for further improvement in these equations since the height alone is inadequate to explain the period variability. The aim of this study is to find the effects of a number of bays in both the directions, the stiffness of the structure and propose a new period equation which incorporates a number of bays, plan area, stiffness along with the height of the structure.

Key Words
number of bay; dynamic analysis; period of vibration; stiffness; plan area

Address
Prakash Sangamnerkar: M.P. Housing and Infrastructure Development Board, Bhopal (M.P.), India
S.K. Dubey: Maulana Azad National Institute of Technology, Bhopal (M.P.), India

Abstract
This paper presents a comparison of the black-box and the physics based derived gray-box models for subspace identification for structures subjected to support-excitation. The study compares the damage detection capabilities of both these methods for linear time invariant (LTI) systems as well as linear time-varying (LTV) systems by extending the gray-box model for time-varying systems using short-time windows. The numerically simulated IASC-ASCE Phase-I benchmark building has been used to compare the two methods for different damage scenarios. The efficacy of the two methods for the identification of stiffness parameters has been studied in the presence of different levels of sensor noise to simulate on-field conditions. The proposed extension of the gray-box model for LTV systems has been shown to outperform the black-box model in capturing the variation in stiffness parameters for the benchmark building.

Key Words
subspace identification; support-excited structures; time-varying systems; damage-detection

Address
Diptojit Datta and Anjan Dutta:Department of Civil Engineering, Indian Institute of Technology Guwahati, Guwahati-781039, India

Abstract
Structural health monitoring (SHM) is a necessity for reliable and efficient functioning of engineering systems. Damage detection (DD) is a crucial component of any SHM system. Lamb waves are a popular means to DD owing to their sensitivity to small damages over a substantial length. This typically involves an active sensing paradigm in a pitch-catch setting, that involves two piezo-sensors, a transmitter and a receiver. In this paper, we propose a data-intensive DD approach for beam structures using high frequency signals acquired from beams in a pitch-catch setting. The key idea is to develop a statistical learning-based approach, that harnesses the inherent sparsity in the problem. The proposed approach performs damage detection, localization in beams. In addition, quantification is possible too with prior calibration. We demonstrate numerically that the proposed approach achieves 100% accuracy in detection and localization even with a signal to noise ratio of 25 dB.

Key Words
sparsity; lamb waves; damage detection; statistical learning

Address
Debarshi Sen: Department of Civil and Environmental Engineering, Rice University, 6100 Main Street, MS 318,
Houston, TX 77005, USA
Debarshi Sen and Satish Nagarajaiah:Department of Mechanical Engineering, Rice University, 6100 Main Street, MS 318, Houston, TX 77005, USA
S. Gopalakrishnan: Department of Aerospace Engineering, Indian Institute of Science, CV Raman Road, Bangalore
560012, India


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