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CONTENTS
Volume 1, Number 2, June 2014
 

Abstract
Real-time near and far-field monitoring of concrete structural components gives enough information on the time and condition at which damage occurs, thereby facilitating damage detection while in the same time evaluate the cause of the damage. This paper experimentally investigates an integrated monitoring technique for near and far-field damage detection in concrete structures based on simultaneous use of electromechanical admittance technique in combination with guided wave propagation. The proposed sensing system does not measure the electromechanical admittance itself but detect time variations in output voltages of the response signal obtained across the electrodes of piezoelectric transducers bonded on surfaces of concrete structures. The damage identification is based on the spectral estimation MUSIC algorithm. Experimental results show the efficiency and performance of the proposed measuring technique.

Key Words
electromechanical admittance; guided waves; concrete beam structures; PZT patches; chirp signal; fourier transform

Address
Costas Providakis, K. Stefanaki, M. Voutetaki, and M. Stavroulaki: Applied Mechanics Lab, School of Architectural Engineering, Technical University of Crete, GR-73100 Chania, Greece
J. Tsompanakis: School of Environmental Engineering Technical University of Crete, GR-73100 Chania, Greece

Abstract
We describe the application of a distributed optical fiber sensor based on stimulated Brillouin scattering, as an integrated system for safety monitoring of railway infrastructures. The strain distribution was measured statically and dynamically along 60 meters of rail track, as well as along a 3-m stone arch bridge. We show that, gluing an optical fiber along the rail track, traffic monitoring can be performed in order to identify the train passage over the instrumented sector and determine its running conditions. Furthermore, dynamic and static strain measurements on a rail bridge are reported, aimed to detect potential structural defects. The results indicate that distributed sensing technology represents a valuable tool in railway traffic and safety monitoring.

Key Words
optical fiber measurements; brillouin scattering; structural health monitoring

Address
Aldo Minardo, Agnese Coscetta and Luigi Zeni:Department of Industrial and Information Engineering, Second University of Naples, Via Roma 29 Aversa, Italy
Giuseppe Porcaro: Tecnomatica SaS, Corso del Mezzogiorno III trav. 71122 Foggia, Italy
Daniele Giannetta: Ferrovie del Gargano, Direzione di Esercizio – 71016 San Severo - Foggia, Italy
Romeo Bernini: Istituto per il Rilevamento Elettromagnetico dell\'Ambiente – Consiglio Nazionale delle Ricerche,
Via Diocleziano, 328 – 80124 Napoli, Italy


Abstract
Scour is one of the leading causes of overwater bridge failures worldwide. While monitoring systems have already been implemented or are still being developed, they suffer from limitations such as high costs, inaccuracies, and low reliability, among others. Also, most sensors only measure scour depth at one location and near the pier. Thus, the objective is to design a simple, low cost, scour hole topography monitoring system that could better characterize the entire depth, shape, and size of bridge scour holes. The design is based on burying a robust, waterproofed, piezoelectric sensor strip in the streambed. When scour erodes sediments to expose the sensor, flowing water excites it to cause the generation of time-varying voltage signals. An algorithm then takes the time-domain data and maps it to the frequency-domain for identifying the sensor\'s resonant frequency, which is used for calculating the exposed sensor length or scour depth. Here, three different sets of tests were conducted to validate this new technique. First, a single sensor was tested in ambient air, and its exposed length was varied. Upon verifying the sensing concept, a waterproofed prototype was buried in soil and tested in a tank filled with water. Sensor performance was characterized as soil was manually eroded away, which simulated various scour depths. The results confirmed that sensor resonant frequencies decreased with increasing scour depths. Finally, a network of 11 sensors was configured to form a distributed monitoring system in the lab. Their exposed lengths were adjusted to simulate scour hole formation and evolution. Results showed promise that the proposed sensing system could be scaled up and used for bridge scour topography monitoring.

Key Words
bridge scour; distributed sensing; piezoelectric sensor; scour monitoring; thin film; vibration monitoring

Address
Kenneth J. Loh, Caroline Tom, Joseph L. Benassini and Fabián A. Bombardelli: Department of Civil and Environmental Engineering, University of California, Davis, One Shields Avenue, 2001 Ghausi Hall, Davis, CA 95616, USA

Abstract
An investigation of tunnel linings is performed at two tunnels in the US using complimentary noncontact techniques: air-coupled ground penetrating radar (GPR), and a vehicle-mounted scanning system (SPACETEC) that combines laser, visual, and infrared thermography scanning methods. This paper shows that a combination of such techniques can maximize inspection coverage in a comprehensive and efficient manner. Since ground-truth is typically not available in public tunnel field evaluations, the noncontact techniques used are compared with two reliable in-depth contact nondestructive testing methods: ground-coupled GPR and ultrasonic tomography. The noncontact techniques are used to identify and locate the reinforcement mesh, structural steel ribs, internal layer interfaces, shallow delamination, and tile debonding. It is shown that this combination of methods can be used synergistically to provide tunnel owners with a comprehensive and efficient approach for monitoring tunnel lining conditions.

Key Words
ground penetrating radar; infrared thermography; structural health monitoring; ultrasonic tomography; nondestructive testing; tunnel lining

Address
Joshua White and Stefan Hurlebaus:Zachry Department of Civil Engineering, Texas A&M University, 3136 TAMU, College Station, TX 77843, USA;
Texas A&M Transportation Institute, Texas A&M University System, 3135 TAMU, College Station, TX 77843, USA
Parisa Shokouhi: Federal Institute for Material Research and Testing (BAM), Unter den Eichen 87, 12205 Berlin, Germany
Andreas Wittwer: SPACETEC Datengewinnung GmbH, Salzstrabe 47, 79098 Freiburg, Germany

Abstract
A novel real-time actuator failure detection algorithm is developed in this paper. Actuator fails when the input to the structure is different from the commanded one. Previous research has shown that one error function can be formulated for each actuator through interaction matrix method. For output without noise, non-zero values in the actuator functions indicate the instant failure of the actuator regardless the working status of other actuators. In this paper, it is further demonstrated that the actuator\'s error function coefficients will be directly calculated from the healthy input of the examined actuator and all outputs. Hence, the need for structural information is no longer needed. This approach is termed as direct method. Experimental results from a NASA eight bay truss show the successful application of the direct method for isolating and identifying the real-time actuator failure. Further, it is shown that the developed method can be used for real-time sensor failure detection.

Key Words
actuator failure; sensor failure; direct method; interaction matrix method

Address
Zhiling Li and Satish Nagarajaiah:Department of civil and environmental engineering, Rice University, Houston, TX, USA, 77005

Abstract
This paper focuses on the dynamic behaviour of Mirandola City Hall (a XV century Renaissance Palace) that was severely damaged during May 2012 Emilia earthquake in Northern Italy. Experimental investigations have been carried out on this monumental building. Firstly, detailed investigations have been carried out to identify the identification of the geometry of the main constructional parts as well as the mechanical features of the constituting materials of the palace. Then, Ambient Vibration Tests (AVT) have been applied, for the detection of the main dynamic features. Three output-only identification methods have been compared: (i) the Frequency Domain Decomposition, (ii) the Random Decrement (RD) and the (iii) Eigensystem Realization Algorithm (ERA). The modal parameters of the Palace were difficult to be identified due to the severe structural damage; however the two bending modes in the perpendicular directions were identified. The comparison of the three experimental techniques showed a good agreement confirming the reliability of the three identification methods.

Key Words
structural health monitoring; output only methods; ambient vibration tests; historical buildings; earthquake damage; frequency domain decomposition; random decrement; Eigensystem Realization Algorithm; ERA; structural health diagnosis and prognosis

Address
Gian Paolo Cimellaro and Alessandro De Stefano: Department of Structural, Geotechnical and Building Engineering (DISEG), Politecnicodi Torino, Torino, Italy


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