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Volume 8, Number 1, March 2021

The assessment of bridges' health has become a relevant component of the maintenance paradigm especially in those countries in which many structures are rated in poor condition and/or are over 50 years old. Additionally, the permanent monitoring of bridges helps engineers in validating the design prediction of bridge structural response to external loads. With more than 600,000 highway bridges, 46.4% of which rated as fair and 7.6% rated in poor condition, United States is one of those countries in which the installation of reliable bridge health monitoring systems is strategically necessary to minimize and optimize repair and rehabilitation costs and to minimize the risk of failures. In this paper, a thorough review of the scientific literature on structural health monitoring systems installed in U.S. bridges over the last 20 years is presented. This review aims to offer interested readers a holistic perspective of recent and current state-of-the-art bridge health monitoring systems and to extract a "general paradigm" that is common to many real structures. The review, conducted through a comprehensive search of peer-reviewed documents available in the scientific literature, discusses more than sixty bridges in terms of the instrumentation used, scope of the monitoring, and main outcomes. Overall, it was found that the monitoring systems provide a valuable tool to compare the structural responses predicted using analytical or numerical tools with the real response of the given structures. Owing to the relative short time span of the monitoring period, most of the monitoring systems did not flag any serious structural flaws that required the closure of the bridge monitored.

Key Words
structural health monitoring; bridges; state-of-the-art review; United States

(1) Piervincenzo Rizzo:
Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA;
(2) Alireza Enshaeian:
Laboratory for Nondestructive Evaluation and Structural Health Monitoring Studies, Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA.

The Gran Sasso National Laboratory (LNGS) is the largest underground research center in the world devoted to neutrino and astroparticle physics. It is located in galleries below about 1400 meters of rock mass. In this environment, inspection and monitoring actions are challenging for the maintenance and the safety of the infrastructures and they require a combined use of different strategies. The paper address issues related to the structural safety of the whole environment by proposing solutions for inspection and monitoring of different areas and elements, such as the gallery vaults, the structures of the experimental prototypes, the plants and the machinery. A generic framework is discussed to evidence the features of each specific solution and the interaction between different systems. Tunnel structural healthy is the most difficult to evaluate because the vaults are coated by not removable panels which waterproof and insulate the environment. Therefore, specific solutions are proposed for the inspection and monitoring of the vaults which are visible only in the interspace realized from such cladding panels. In this respect, different methodologies based on the use of robotic systems are presented and discussed in order to implement a suitable inspection and monitoring program. The complementary requirements to perform a mechatronic survey are defined also as basis of ongoing activities currently performed in LNGS.

Key Words
tunnel survey; underground structures; structural health monitoring; non-destructive testing; robotic systems

(1) Cecilia Rinaldi, Umberto Di Sabatino:
Department of Civil Architectural and Environmental Engineering, University of L'Aquila, via G. Gronchi 18, 67100 L'Aquila, Italy;
(2) Francesco Potenza:
Department of Engineering and Geology, University G. d'Annunzio of Chieti-Pescara, viale Pindaro 42, 65127 Pescara, Italy;
(3) Vincenzo Gattulli:
Department of Structural and Geotechnical Engineering, Sapienza University of Rome, Via Eudossiana 18, 00184 Rome, Italy.

In recent years, damage detection methods have been significantly increased in civil and mechanical structures. One of the most widely used and relatively new methods of signal processing is the method based on wavelet transform; with the help of this powerful tool, the damage in the structures can be detected in the early stages of damage formation, in order to prevent a larger damage event. In this paper, we have investigated the debonding damage of active surfaces in Concrete-Filled Tube (CFT) columns, which greatly reduces the effect of enclosure on concrete and decreases the bearing capacity of these tubes with the help of wavelet transformation (Discrete Wavelet Transform and Continuous Wavelet Transform). The debonding damage of the active surfaces was evaluated using wavelet types, and the occurrence and location of the damage were detected based on variations in frequency and mode shapes. The above studies have been done for the first six modes of the CFT column. The results of the analyzes indicate that the wavelet transform tool is very capable of detecting the occurrence and location of the damage and is able to detect high-level debonding damage in one side of the column that creates curvature and slight jump in the shape of the mode.

Key Words
damage detection; CFT column; active interface debonding; wavelet transform; modal analysis

(1) Adel Younesi, Omid Rezaifar, Majid Gholhaki:
Department of Civil Engineering, Semnan University, Semnan, Iran;
(2) Akbar Esfandiari:
Department of Maritime Engineering, Amir Kabir University, Turkey.

The paper presents damage detection techniques for structural health monitoring of bridges incorporating computer vision derived measurements. The feasibility of the techniques is demonstrated on a numerical model of a bridge girder. The girder is subjected to a load induced by a slowly moving truck. Multiple damage scenarios are simulated. Damage detection is carried out on the four types of response (i.e., deflection, inclination angle, strain and curvature) computed from the numerical model. The robustness of vision measurement approach for damage detection is validated at different levels of added measurement noise. The noise is expressed as the pixel resolution achievable with the image processing algorithm at multiple camera field of views applied to target motions. Damage detection and location accuracies are influenced by damage extent, added measurement noise and type of response. The study shows that deflections and strains outperform inclination angles and curvatures detecting damages in noisy measurements. Strains are the best type of response for damage detection and location when high measurement resolutions (e.g., 1/500 pixels) can be achieved.

Key Words
damage detection; numerical modelling; data interpretation; signal processing; vision-based measurement

(1) Chidiebere B. Obiechefu:
School of Architecture, Design, and the Built Environment, Nottingham Trent University, United Kingdom;
(2) Rolands Kromanis:
Department of Civil Engineering, Faculty of Engineering Technology, University of Twente, Netherlands.

The main purpose of the present paper is to evaluate the influence of increase of the coefficient of viscosity with time on the strain energy release rate for a longitudinal crack in a continuously inhomogeneous beam configuration under linear creep. The beam exhibits continuous material inhomogeneity along the width, thickness and length. The creep behavior is studied analytically by a viscoelastic model structured by one dashpot and three springs. The coefficient of viscosity of the dashpot and the modulii of elasticity of the springs are distributed continuously in the width, thickness and length directions of the beam. Besides, the coefficient of viscosity increases with time. Time-dependent solutions to the strain energy release are derived by considering the balance of the energy and by applying the compliance method. The results obtained by the two solutions are identical which proves the correctness of the analysis performed. The solutions take into account the creep behavior and the increase of the coefficient of viscosity with time. A parametric study of the strain energy release rate is carried-out by using the solutions derived. It is found that the strain energy release rate decreases with increasing of the coefficient of viscosity with time.

Key Words
longitudinal crack; beam structure; viscoelastic behavior; creep; continuous material inhomogeneity

Department of Technical Mechanics, University of Architecture, Civil Engineering and Geodesy, 1 Chr. Smirnensky blvd., 1046 — Sofia, Bulgaria.

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