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CONTENTS
Volume 1, Number 1, March 2014
 

Abstract
The developments and implementations of the structural health monitoring (SHM) system for large infrastructures have been gradually recognized by researchers, engineers and administrative authorities in the last decades. This paper summarizes an updated review on innovations and applications in SHM for infrastructures carried out by researchers at Dalian University of Technology. Invented sensors and data acquisition system are firstly briefly described. And then, some proposed theories and methods including the sensing technology, sensor placement method, signal processing and data fusion, system identification and damage detection are discussed in details. Following those, the activities on the standardization of SHM and several case applications on specific types of structure are reviewed. Finally, existing problems and promising research efforts in the field of SHM are given.

Key Words
structural health monitoring; infrastructure; sensing technology; signal processing; system identification

Address
Hong-Nan Li, Ting-Hua Yi, Liang Ren, Dong-Sheng Li and Lin-Sheng Huo : Faculty of Infrastructure Engineering, Dalian University of Technology, Dalian 116023, China

Abstract
This study has been motivated to examine the performance of a wireless sensor system under the typhoons as well as to analyze the effect of the typhoons on the bridge\'s vibration responses and the variation of cable forces. During the long-term field experiment on a real cable-stayed bridge in years 2011-2012, the bridge had experienced two consecutive typhoons, Bolaven and Tembin, and the wireless sensor system had recorded data of wind speeds and vibration responses from a few survived sensor nodes. In this paper, the wireless structural health monitoring of stay cables under the two consecutive typhoons is presented. Firstly, the wireless monitoring system for cable-stayed bridge is described. Multi-scale vibration sensor nodes are utilized to measure both acceleration and PZT dynamic strain from stay cables. Also, cable forces are estimated by a tension force monitoring software based on vibration properties. Secondly, the cable-stayed bridge with the wireless monitoring system is described and its wireless monitoring capacities for deck and cables are evaluated. Finally, the structural health monitoring of stay cables under the attack of the two typhoons is described. Wind-induced deck vibration, cable vibration and cable force variation are examined based on the field measurements in the cable-stayed bridge under the two consecutive typhoons.

Key Words
structural health monitoring; wireless sensor system; cable-stayed bridge; cable force variation; vibration responses; PZT dynamic strain; wind; typhoon

Address
Jeong-Tae Kim, Thanh-Canh Huynh and So-Young Lee : Department of Ocean Eng., Pukyong National University, Busan, Korea

Abstract
A new output only modal analysis method is developed in this paper. This method uses continuous wavelet transform to modify a popular blind source separation algorithm, second order blind identification (SOBI). The wavelet modified SOBI (WMSOBI) method replaces original time domain signal with selected time-frequency domain wavelet coefficients, which overcomes the shortcomings of SOBI. Both numerical and experimental studies on bridge models are carried out when there are limited number of sensors. Identified modal properties from WMSOBI are analyzed and compared with fast Fourier transform (FFT), SOBI and eigensystem realization algorithm (ERA). The comparison shows WMSOBI can identify as many results as FFT and ERA. Further case study of structural health monitoring (SHM) on an arch bridge verifies the capability to detect damages by combining WMSOBI with incomplete flexibility difference method.

Key Words
bind source separation; flexibility difference; wavelet modified second order blind identification; structural health monitoring

Address
Chaojun Huang: Department of Civil & Environmental Engineering, Rice University, 6100 Main Street, Houston,
Texas-77005, USA
Satish Nagarajaiah: Department of Civil & Environmental Engineering and Department of Mechanical Engineering & Material Science, Rice University, 6100 Main Street, Houston, Texas-77005, USA

Abstract
Structural Health Monitoring (SHM) is an effective alternative to conventional inspections which are time-consuming and subjective. SHM can detect damage early and reduce maintenance cost and thereby help reduce the likelihood of catastrophic structural events to infrastructure such as bridges. After reviewing the Damage Index Method (DIM), an Iterative Damage Index Method (IDIM) is proposed to improve the accuracy of damage detection. These two damage detection techniques are compared based on damage on two structures, a simply supported beam and a pedestrian bridge. Compared to the traditional damage detection algorithm, the proposed IDIM is shown to be less arbitrary and more accurate.

Key Words
vibration-based damage identification method; damage index method; damage detection algorithm; structural health monitoring

Address
Taesun You: Texas A&M Transportation Institute, College Station, TX 77843-3135, USA
Paolo Gardoni: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign,
Urbana, IL61801-2351, USA
Stefan Hurlebaus: Zachry Department of Civil Engineering, Texas A&M University, College Station, TX 77843-3136, USA

Abstract
The increased use of carbon fiber reinforced polymer (CFRP) in retrofitting reinforced concrete (RC) members has led to the need to develop non-destructive techniques that can monitor and characterize the unique damage mechanisms exhibited by such structural systems. This paper presented the damage characterization results of six CFRP retrofitted RC beam specimens tested in the laboratory and monitored using acoustic emission (AE). The focus of this study was to continuously monitor the change in AE parameters and analyze them both qualitatively and quantitatively, when brittle failure modes such as debonding occur in these beams. Although deterioration of structural integrity was traceable and can be quantified by monitoring the AE data, individual failure mode characteristics could not be identified due to the complexity of the system failure modes. In all, AE was an effective non-destructive monitoring tool that can trace the failure progression in RC beams retrofitted with CFRP. It would be advantageous to isolate signals originating from the CFRP and concrete, leading to a more clear understanding of the progression of the brittle damage mechanism involved in such a structural system. For practical applications, future studies should focus on spectral analysis of AE data from broadband sensors and automated pattern recognition tools to classify and better correlate AE parameters to failure modes observed.

Key Words
acoustic emission; reinforced concrete; CFRP; intensity analysis

Address
Archana Nair, C.S. Cai, Fang Pan and Xuan Kong :Department of Civil and Environmental Engineering, Louisiana State University, Baton Rouge, LA, 70803, USA

Abstract
Special track systems used to divert a train to other directions or other tracks are generally called \'railway turnout\'. A traditional turnout system consists of steel rails, switches, crossings, steel plates, fasteners, screw spikes, timber bearers, ballast and formation. The wheel rail contact over the crossing transfer zone has a dip-like shape and can often cause detrimental impact loads on the railway track and its components. The large impact also emits disturbing noises (either impact or ground-borne noise) to railway neighbors. In a brown-field railway track where an existing aged infrastructure requires renewal or maintenance, some physical constraints and construction complexities may dominate the choice of track forms or certain components. With the difficulty to seek for high-quality timbers with dimensional stability, a methodology to replace aged timber bearers in harsh dynamic environments is to adopt an alternative material that could mimic responses and characteristics of timber in both static and dynamic loading conditions. A critical review has suggested an application of an alternative material called fibre-reinforced foamed urethane (FFU). The full-scale capacity design makes use of its comparable engineering characteristics to timber, high-impact attenuation, high damping property, and a longer service life. A field trial to investigate in-situ behaviours of a turnout grillage system using an alternative material, \'fibre-reinforced foamed urethane (FFU)\' bearers, has been carried out at a complex turnout junction under heavy mixed traffics at Hornsby, New South Wales, Australia. The turnout junction was renewed using the FFU bearers altogether with new special track components. Influences of the FFU bearers on track geometry (recorded by track inspection vehicle

Key Words
fibre-reinforced foamed urethane bearers; field trial; railway turnout grillage; track geometry; stability; vibration; material design and analysis; performance monitoring

Address
Sakdirat Kaewunruen : RailCorp – Track Engineering Level 13, 477 Pitt St., Sydney NSW 2000 Australia


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