99 results on '"Farhad Ansari"'
Search Results
2. Micro-crack detection method of steel beam surface using stacked autoencoders on massive full-scale sensing strains
- Author
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Qingsong Song, Yu Chen, Guangwu Tang, Elias Abdoli Oskoui, Xiangmo Zhao, Todd Taylor, Zheng Fang, and Farhad Ansari
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Surface (mathematics) ,Materials science ,business.industry ,Mechanical Engineering ,Biophysics ,Micro cracks ,Full scale ,020101 civil engineering ,02 engineering and technology ,01 natural sciences ,0201 civil engineering ,010309 optics ,Brillouin zone ,Optics ,Fiber optic sensor ,0103 physical sciences ,Pattern recognition (psychology) ,Structural health monitoring ,business ,Beam (structure) - Abstract
Accurate micro-crack detections on the whole surface of civil structures have great significance. Distributed optical fiber sensor based on Brillouin optical time-domain analysis technology exhibits great facility to measure strain distributions along the whole surface of structures with a high spatial resolution, thus providing a potential and competitive solution to the detection problem. However, mainly due to low signal-to-noise ratio in measurements, such sensor system is still limited in crack detection–based structural health monitoring applications. How to extract high-quality micro-crack feature representations from the low signal-to-noise ratio–distributed strain measurements is crucial to solve the problem. It has been demonstrated in field of pattern recognition that deep learning can automatically extract high-quality noise-robust feature representations from mass chaos data. Therefore, a micro-crack detection method is proposed herein based on deep learning to analyze the full-scale strain measurements. Each measurement is normalized and segmented into a set of equal-length subsequences. Autoencoders, a typical kind of building block of deep neural network, are stacked layer-wise into a deep network and then exploited to automatically extract feature representations from the subsequences. Each extracted feature representation is labeled as one of the two categories by a Softmax regression. One category originates in the subsequences acquired from structure sections with crack defects and another from sections without any cracks. The micro-crack detections are achieved by solving such a crack/non-crack binary classification problem. A 15-m-long steel I-beam with artifact crack defects is built up in laboratory to verify the proposed method. Experimental results demonstrate that the minimum size of detectable crack opening width reaches to 23 μm, and besides, the proposed method is significantly better than traditional Fisher linear discriminant analysis method and classical support vector machine on the detection accuracy. more...
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- 2019
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3. Method and sensor for monitoring weight of trucks in motion based on bridge girder end rotations
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Elias Abdoli Oskoui, Todd Taylor, and Farhad Ansari
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Truck ,021110 strategic, defence & security studies ,Influence line ,business.industry ,Rotation sensor ,Computer science ,Mechanical Engineering ,0211 other engineering and technologies ,Motion (geometry) ,020101 civil engineering ,Ocean Engineering ,02 engineering and technology ,Building and Construction ,Structural engineering ,Geotechnical Engineering and Engineering Geology ,Bridge (nautical) ,0201 civil engineering ,Monitoring weight ,Axle ,Girder ,Safety, Risk, Reliability and Quality ,business ,Civil and Structural Engineering - Abstract
Traffic monitoring, including the estimation of axle and gross vehicle weights of passing trucks over bridges plays an important role in the determination of actual service loads. Knowledge of thes... more...
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- 2019
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4. Method and monitoring approach for distributed detection of damage in multi-span continuous bridges
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Farhad Ansari, Elias Abdoli Oskoui, and Todd Taylor
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Sensor system ,Normalization (statistics) ,Influence line ,Optical fiber ,Computer science ,business.industry ,0211 other engineering and technologies ,Box girder ,020101 civil engineering ,02 engineering and technology ,Structural engineering ,computer.software_genre ,0201 civil engineering ,law.invention ,Load testing ,law ,Brillouin scattering ,Precast concrete ,021105 building & construction ,business ,computer ,Civil and Structural Engineering - Abstract
A method for distributed detection of damage along the lengths of multi-span continuous Bridges is introduced. It is based on monitoring the distributed strains along the length of the bridge by using Brillouin scattering based optical fiber sensors. Identification of damage beyond the signal to noise limits of the instrument is achieved by normalization of the measured distributed strains during multiple positions of a truck with respect to the theoretical influence line of the bridge. Formulation of the method leads to the introduction of a damage index for identification of microcrack locations along the spans of the Bridge. Effectiveness of the proposed method was evaluated by load testing of a five span continuous precast post-tensioned concrete box girder bridge. Locations of detected microcracks by the distributed sensor system were further verified by visual inspections. more...
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- 2019
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5. Structural crack identification method based on dynamic distributed strain monitoring
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Farhad Ansari, Wenjing Wu, and Xin Feng
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Optical fiber ,Strain (chemistry) ,business.industry ,Computer science ,Process (computing) ,Structural engineering ,Signal ,law.invention ,Identification (information) ,law ,Component (UML) ,mental disorders ,Harmonic ,business ,Strain monitoring - Abstract
Due to the factors such as environment, material aging, and fatigue loads, structural members are prone to crack damage during the service, which could lead to the risk of collapse as the crack-induced strain accumulates. This paper proposes a method for structural crack identification and location based on a distributed optical fiber dynamic strain monitoring method. The Savitzky-Golay smooth filtering method was used to extract the crack information from the obtained dynamic strain signal. Based on the local strain anomaly of the structure and the nonlinear vibration characteristics of the "breathing" crack model, the cracks distributed along the structure can be located. According to the change of harmonic component, the crack development process can be identified, and early identification and localization of structural cracks during operation can be realized, which provides a practical approach of the damage monitoring for the cracked structures. more...
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- 2020
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6. Fiber optic distributed sensor for condition monitoring of underground concrete structures
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Yang Zhao, Ming Zhao, and Farhad Ansari
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Materials science ,Optical fiber ,business.industry ,Tension (physics) ,Composite number ,Condition monitoring ,Structural engineering ,Fibre-reinforced plastic ,law.invention ,Fiber optic sensor ,law ,Deformation (engineering) ,business ,Reduction (mathematics) - Abstract
A distributed fiber optic sensor is developed for condition monitoring of civil infrastructure systems. The fiber optic sensor is especially useful in applications involving underground structures and elements, i.e. concrete pipes, since they can be embedded within the structural elements and operated remotely. The sensor principles are simple and therefore, practical for crack detection and deformation measurement in civil structural applications. Structural monitoring capability of the sensor was evaluated through experiments with reinforced concrete beams, which were repaired by fiber reinforced polymer (FRP) composite materials. The objective was to test the strain reduction capability of the system in applications involving composite structures. The sensor was adhered to the surface of FRP composite, and in the tension zone of the beams. Experimental results are presented and discussed. more...
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- 2020
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7. Analysis the temperature effect on the output polarization degree of the fiber Lyot depolarizer
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Tong Yao Du, Yong Kong, Farhad Ansari, and Yong Qi Wang
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Materials science ,Birefringence ,business.industry ,Gyroscope ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Fiber raman amplifier ,Thermal coefficient ,Polarization (waves) ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,010309 optics ,Fiber sensor ,Optics ,law ,0103 physical sciences ,Degree of polarization ,Electrical and Electronic Engineering ,0210 nano-technology ,business - Abstract
First, the temperature effect on the output polarization degree of the fiber Lyot depolarizer was analyzed in this paper theoretically, which shows that when the environment temperature changes from −40℃ to 80℃, the degree of the output light polarization (DOP) of the fiber Lyot depolarizer will increase until about 70℃, then DOP begin to decrease. The further numerical simulations indicate that this result was caused together by thermally induced group birefringence and thermal coefficient of expansion of the polarization fiber. Using our made fiber Lyot depolarizer (DOP≤0.3% when the environment temperature is 20℃), DOP of the fiber Lyot depolarizer was studied at the condition of a variable temperature experimentally, the results are in agreement with the related theoretically results basically, at last, the difference between theoretical and experimental results is discussed, the possible methods to reduce the influence of the temperature on the output DOP of fiber Lyot depolarizer is presented in this paper. It is a good guiding significance to improve the depolarization performance of the fiber Lyot depolarizer in the fields of fiber sensor, fiber gyroscope, fiber Raman amplifier and so on as we believe. more...
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- 2019
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8. Visual saliency–based image binarization approach for detection of surface microcracks by distributed optical fiber sensors
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Qingsong Song, Elias Abdoli Oskoui, Farhad Ansari, and Todd Taylor
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Surface (mathematics) ,Optical fiber ,business.industry ,Computer science ,Mechanical Engineering ,Biophysics ,020101 civil engineering ,02 engineering and technology ,Similarity measure ,01 natural sciences ,0201 civil engineering ,Image (mathematics) ,law.invention ,010309 optics ,Brillouin scattering ,law ,0103 physical sciences ,Pattern recognition (psychology) ,Computer vision ,Artificial intelligence ,Structural health monitoring ,business ,Image resolution - Abstract
Early detection of defects and anomalies is important for safety and efficient management of structural elements. Brillouin scattering–based optical fiber sensors provide distributed sensing capabilities by monitoring the strain and temperature over large distances in structural elements. Their use has been limited to oil and gas explorations, mainly due to the inherent low signal-to-noise ratio in such systems, preventing detection of microcracks in structural monitoring applications. This study introduces a method based on the visual saliency approach through which the digital images acquired by the distributed strain data are employed for the detection of surface microcracks. When using this method, strain data sequences along the entire length of a structural element are sampled with a Brillouin scattering–based optical fiber sensor and then divided into a set of equal-length subsequences. A similarity measure matrix is composed based on the distributed strain data and then converted into a grayscale image. The saliency maps of the acquired grayscale images are calculated and a center-hollowed square template is defined and exploited for convolution with the binarized saliency map as a filter operator. The pixels retained after the filtering correspond to the locations of microcracks. Verification of the method was accomplished by experiments on a 15-m-long steel beam with fabricated defects. more...
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- 2018
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9. Distributed detection of microcracks by differential narrowing of FWHM in BFS
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Yong Kong, Farhad Ansari, and Yi Shi
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Optical fiber ,Materials science ,business.industry ,02 engineering and technology ,01 natural sciences ,Noise (electronics) ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,010309 optics ,Brillouin zone ,Full width at half maximum ,020210 optoelectronics & photonics ,Signal-to-noise ratio ,Optics ,law ,Brillouin scattering ,0103 physical sciences ,0202 electrical engineering, electronic engineering, information engineering ,Time domain ,Electrical and Electronic Engineering ,business ,Image resolution - Abstract
Brillouin scattering based optical fiber sensors provide the opportunity for distributed detection of multiple cracks in structures. Because of capability for making high spatial resolution measurements, pre-pump-pulse Brillouin optical time domain analysis (PPP-BOTDA) systems have been successful in detecting microcracks. Recent studies have shown that when the space between two neighboring microcracks is smaller than the full width at half maximum (FWHM) of the peaks in Brillouin frequency shift (BFS), the strain peaks in BFS interfere, and inhibit detection of multiple microcracks. The focus of the present study is to narrow the size of FWHM by computing the difference in BFS of the strain peaks at two slightly different spatial resolutions. The differential FWHM obtained in this manner is narrower than the original FWHM for single microcrack, as well as two neighboring microcracks. The efficiency of the proposed approach was tested through experiments. The results indicated that it was possible to reduce the FWHM for single cracks, and also to detect the presence of dual microcracks with crack spacing distances smaller than the FWHM. However, the effectiveness of the proposed approach is also dependent on the spatial resolution of measurements, and the signal to noise ratio of the measurement system. While higher spatial resolutions are required for effective narrowing of FWHM in differential approach, the measurement noise at higher spatial resolutions limited the applicability of the method for very small crack opening displacements. more...
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- 2018
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10. Structural response of a cable-stayed bridge subjected to lateral seismic excitations
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Farhad Ansari, Amr Z. Elkady, and Maryam Ayman Seleemah
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business.industry ,Shear force ,020101 civil engineering ,02 engineering and technology ,Structural engineering ,Resonance (particle physics) ,Bridge (interpersonal) ,Displacement (vector) ,0201 civil engineering ,Deck ,Acceleration ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Structural health monitoring ,Safety, Risk, Reliability and Quality ,business ,Scale model ,Geology ,Civil and Structural Engineering - Abstract
Cable-stayed bridges are structurally efficient and offer cost effective solutions in medium to large-span crossings. The study reported in this article aimed at determining the behavior of a typical cable-stayed bridge when subjected to lateral earthquake excitations. A hybrid analytical–experimental technique is introduced to experimentally simulate the earthquake excitations on the bridge. In this technique, displacement time history of the bridge mid-span was first obtained analytically by exciting the bridge using the earthquake acceleration records. To experimentally simulate the earthquake excitations, these displacements were applied on a $$ \frac{1}{60} $$ scale model of a single plane cable-stayed bridge using a displacement controlled shaker. The efficiency of this technique was evaluated by comparing the experimental versus analytical response in terms of dynamic characteristics and displacement responses of the bridge. The analytical response of the bridge served as a verification tool for validation of key response parameters of the full-scale bridge. These parameters included forces in cables, strains and stresses in the deck, and moments and shear forces acting on pylons in the transverse direction. more...
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- 2018
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11. Machine-learning-based approach for post event assessment of damage in a turn-of-the-century building structure
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Tian Weifeng, Farhad Ansari, Ebrahim Nazarian, and Todd Taylor
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Artificial neural network ,Settlement (structural) ,business.industry ,Event (computing) ,Computer science ,0211 other engineering and technologies ,020101 civil engineering ,02 engineering and technology ,Masonry ,Machine learning ,computer.software_genre ,0201 civil engineering ,Support vector machine ,Naive Bayes classifier ,Load testing ,021105 building & construction ,Artificial intelligence ,Structural health monitoring ,Safety, Risk, Reliability and Quality ,business ,computer ,Civil and Structural Engineering - Abstract
The work presented in this article describes development of a machine learning (ML)-based platform for condition assessment of building structures in the aftermath of extreme events. The methods employed in the study include support vector machines, neural networks, and Gaussian Naive Bayes techniques for training of the structural health monitoring model. The ML platform relates the change in stiffness, and strains in various structural components of the system to the intensity and location of damage. Evaluation of the proposed method was accomplished by using it for the characterization of damage in a turn-of-the-century, six-story building with timber frames and masonry walls. The building was damaged due to differential settlement of its foundation. Application of the proposed method in the building required load testing of selected structural elements, and use of the strains acquired from the field tests as input to the ML model. more...
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- 2018
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12. Research on theϕ-OTDR fiber sensor sensitive for all of the distance
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Yi Shi, Farhad Ansari, Yong Kong, Yang Liu, and Todd Taylor
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Mode volume ,Amplified spontaneous emission ,Materials science ,business.industry ,Physics::Optics ,Polarization-maintaining optical fiber ,02 engineering and technology ,Optical time-domain reflectometer ,01 natural sciences ,Graded-index fiber ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,010309 optics ,020210 optoelectronics & photonics ,Optics ,Fiber Bragg grating ,Fiber optic sensor ,0103 physical sciences ,0202 electrical engineering, electronic engineering, information engineering ,Dispersion-shifted fiber ,Electrical and Electronic Engineering ,Physical and Theoretical Chemistry ,business - Abstract
In this paper, a modified construction for the traditional ϕ -OTDR fiber sensor sensitive for all of distance is presented, the related numerical simulation and experiment analysis results show that this construction can reduce the gain imbalance for all of the distance along the fiber caused by the Rayleigh scattering loss of the fiber and the gain imbalance of Raman fiber amplifier in this fiber sensor system. In order to improve further the vibration sensitivity of this system, the possible methods to restrain the influences of modulation instability effect, Stimulated Brillouin effect, reduce the amplified spontaneous emission (ASE) noises of Raman laser (RL) and Erbium3+-doped fiber amplifiers (EDFA), double Rayleigh backscattering noise in this system are discussed, which will offer a great reference value for the science research and engineering application in the field of fiber sensor as we believe. more...
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- 2018
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13. Crack Detection Using Embedded Fiber-Optic Sensors in Reinforced Concrete Beams
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Alessandro Cardoni, Daniele Inaudi, Farhad Ansari, Marco Domaneschi, Ivan Cottone, and Gian Paolo Cimellaro
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Optical fiber ,business.industry ,Computer science ,020101 civil engineering ,02 engineering and technology ,Structural engineering ,Reinforced concrete ,01 natural sciences ,0201 civil engineering ,law.invention ,Cracking ,Fiber optic sensor ,law ,0103 physical sciences ,Ultimate tensile strength ,Limit state design ,Deformation (engineering) ,business ,010301 acoustics ,Beam (structure) - Abstract
Reinforced concrete structural components such as beams are subject during their service life to different loading conditions that may affect their durability and efficiency. This can reduce the safety level of the structure over time until it degrades completely and reaches its ultimate limit state. In particular, cracking conditions due to tensile conditions can be developed leading to the exposure of the steel reinforcements to the aggression of external agents, such as chlorides. Being able to monitor the development and the evolution of cracking is crucial and this research is aimed at this purpose. In particular, laboratory tests have been performed on reinforced concrete beams equipped with distributed fiber optics sensors to monitor the state of cracking. This technology has been selected because its inherent accuracy and low noise. Furthermore, since technology relies of optical signals, the sensors are not affected by electrical and magnetic noise. They are also resistant to high temperatures and chemically reactive environments. The main objectives of the presented first part of this research are focused on the deformation and temperature assessment after concrete pouring, crack detection, localization and opening quantification. more...
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- 2019
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14. Dynamic Characterization and Vulnerability Assessment of a School Building in Italy
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Alessandro Cardoni, Valentina Villa, Gian Paolo Cimellaro, Carlo Caldera, Sebastiano Marasco, Marco Domaneschi, Farhad Ansari, and Ali Zamani Noori
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Signal processing ,Computer science ,business.industry ,Noise (signal processing) ,020101 civil engineering ,02 engineering and technology ,01 natural sciences ,Finite element method ,0201 civil engineering ,Reliability engineering ,Building information modeling ,Vulnerability assessment ,0103 physical sciences ,Thermal ,Structural health monitoring ,business ,Environmental noise ,010301 acoustics ,Reliability (statistics) - Abstract
The accuracy of structural models significantly depends on the availability of input design parameters such as the dimensions of resisting elements, material properties, joint connection details, loading conditions, etc. When dealing with old structures, a lot of this information is not accessible, which leads to the introduction of many uncertainties into the model. In the last few decades, several structural health monitoring (SHM) techniques have been used to compensate such lack of data and perform more reliable structural analyses. However, SHM might result in costly and time-consuming surveys that can be as well affected by uncertainties due to environmental effects, measurement noise, and signal processing errors. This paper discusses and introduces a straightforward SHM procedure to collect the fundamental information to achieve a better accuracy and reliability of the finite element model of the considered building. The methodology starts with the acquisition of structural data from available construction drawings and Building Information Modeling (BIM) to create a preliminary finite element model. Then a series of non-destructive tests are performed using thermal camera, sclerometer, pachometer to identify the fundamental structural parameters. In addition, environmental noise measured through accelerometers is used to determine the principal frequencies of the structure. Harmonic excitations are then horizontally applied to resisting elements using a vibrodyne. The proposed methodology was tested on an RC school building located in Melzo (Milan, Italy). Statistical and signal processing techniques are then utilized to interpret the acquired signals and consequently update and calibrate the structural model for the vulnerability assessment. The processed signals revealed substantial differences with the original FE model. Thus, rigidity, mass and damping were modified accordingly. more...
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- 2019
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15. Structural monitoring and remaining fatigue life estimation of typical welded crack details in the Manhattan Bridge
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Zheng Fang, Todd Taylor, Emad Norouzzadeh Tochaei, Saeed Babanajad, and Farhad Ansari
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business.industry ,Computer science ,Probabilistic logic ,Structural engineering ,Welding ,Bridge (interpersonal) ,law.invention ,Axle ,law ,Train ,Structural health monitoring ,business ,Reliability (statistics) ,Structural monitoring ,Civil and Structural Engineering - Abstract
Manhattan Bridge is a suspension structure that connects Manhattan to Downtown Brooklyn. This bridge is over 110 years old and subjected to daily repeated axles of transit trains and other vehicular traffic. Visual inspections of the bridge revealed manifestation of many cracks in the welded details due to the out-of-plane forces at the connections between transit and floor beams. The research reported herein, pertains to the fatigue life evaluation and reliability assessment of typical cracked welded details. The bridge was instrumented with a real-time structural health monitoring system based on FBG sensors for remote monitoring of the cracked connections. Both deterministic and probabilistic approaches were employed for prediction of the remaining fatigue life of typical cracked details. For the same fatigue reliability index of 2.3, the deterministic and probability based methods yielded remaining fatigue life of 369 and 120 years, respectively, for the typical welded connections details of the bridge. more...
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- 2021
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16. Distributed monitoring method for upheaval buckling in subsea pipelines with Brillouin optical time-domain analysis sensors
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Dewei Meng, Xin Feng, Jing Zhou, Farhad Ansari, and Wenjing Wu
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Engineering ,Optical fiber ,business.industry ,020101 civil engineering ,02 engineering and technology ,Building and Construction ,Structural engineering ,01 natural sciences ,0201 civil engineering ,law.invention ,010309 optics ,Brillouin zone ,Pipeline transport ,Buckling ,law ,0103 physical sciences ,Monitoring methods ,Time domain ,Structural health monitoring ,business ,Civil and Structural Engineering ,Subsea - Abstract
A method for monitoring the upheaval buckling of subsea buried pipelines by distributed optical fiber sensors is introduced. The proposed method originates from the fact that the bucked pipe has the deterministic patterns of the bending-induced and axial force–induced strains, which can be used to identify the pre- and post-buckling states of the pipe. The challenge for utilizing these features is that the distributed fiber optic sensor can only measure the compound strain created by both bending and axial compression. A monitoring scheme by placing three sensors with [Formula: see text] space around the circumference of the pipeline was proposed in this article. An approach was presented to extract the bending-induced and axial force–induced strains from the longitudinal strains measured by the distributed fiber optic sensors. The experimental programs were then designed to investigate the feasibility of the proposed method. It is demonstrated that the proposed method is possible to detect the occurrence of buckling in the pipe. However, further research is necessary in order to examine the efficiency of the proposed approach under the complex loading patterns at subsea levels. more...
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- 2016
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17. Effects of near-field ground motions and soil-structure interaction on dynamic response of a cable-stayed bridge
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Emad Norouzzadeh Tochaei, Farhad Ansari, and Todd Taylor
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business.industry ,Numerical analysis ,0211 other engineering and technologies ,Foundation (engineering) ,Soil Science ,Stiffness ,020101 civil engineering ,Near and far field ,02 engineering and technology ,Structural engineering ,Geotechnical Engineering and Engineering Geology ,Bridge (interpersonal) ,0201 civil engineering ,Soil structure interaction ,medicine ,Cable stayed ,medicine.symptom ,business ,Scale model ,Geology ,021101 geological & geomatics engineering ,Civil and Structural Engineering - Abstract
Seismic response of cable-stayed bridges is investigated with the main focus pertaining to the effects of near-field ground motions and soil-structure interaction on the dynamic response of the bridges. A 1/60 scale model of a typical cable-stayed bridge was designed and fabricated for the laboratory investigations. Three different types of ground motion records from the 1999 Chi-Chi earthquake, namely far-field, non-pulse near-field, and pulse-type near-field were employed in the experiments and the numerical analysis of the bridge. Laboratory simulation of the soil-structure interaction was accomplished by a box-spring system with interchangeable springs as foundations for the bridge towers. A three-dimensional numerical model of the bridge was developed, and its response was verified by the experimental results. Results from the numerical and experimental investigations indicated that the effects of foundation soil stiffness on the response of the bridge was influenced by the type of input ground motions. The bridge response was amplified when their foundation was in softer soils. more...
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- 2020
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18. Deep learning method for detection of structural microcracks by brillouin scattering based distributed optical fiber sensors
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Qingsong Song, Guangwu Tang, Chao Zhang, and Farhad Ansari
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Optical fiber ,business.industry ,Computer science ,Deep learning ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,law.invention ,Optics ,Mechanics of Materials ,Brillouin scattering ,law ,Signal Processing ,General Materials Science ,Artificial intelligence ,Structural health monitoring ,Electrical and Electronic Engineering ,business ,Civil and Structural Engineering - Published
- 2020
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19. Out-of-plane seismic behavior of cast-in-situ composite wall with metal tailing porous concrete
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Chao Li, Pengfei Liu, Hong-Nan Li, Farhad Ansari, and Gang Li
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Materials science ,business.industry ,Numerical analysis ,Composite number ,Pervious concrete ,0211 other engineering and technologies ,020101 civil engineering ,02 engineering and technology ,Structural engineering ,Masonry ,Finite element method ,0201 civil engineering ,Metal ,visual_art ,021105 building & construction ,Thermal ,visual_art.visual_art_medium ,Earthquake shaking table ,business ,Civil and Structural Engineering - Abstract
The out-of-plane seismic behavior of infilled walls has attracted increasing attention in recent years. As a newly-developed infilled wall, the cast-in-situ composite wall with the metal tailing porous concrete (CCWMTPC) possesses better thermal performance than the conventional masonry infilled walls. In this article, the out-of-plane seismic behavior of CCWMTPC is investigated by a series of shaking table tests. The specimen includes a steel frame with two infilled CCWMTPCs. With increase of the peak ground accelerations of four different input excitations, the peak out-of-plane accelerations and peak relative displacements measured at the mid-height and top of the CCWMTPCs exhibited linear response. The CCWMTPCs were not damaged. The experimental results revealed that the CCWMTPCs were still within their elastic state following the input excitations. Subsequently, the specimen was excited harmonically by the sine-waves until some level of damage was observed. A numerical analysis by the finite elements was performed in order to evaluate the experimental results and to compare the behavior of the CCWMTPC with the conventional masonry infilled walls. Results indicated that the out-of-plane performance of CCWMTPC under input excitations is better than their masonry counterparts. more...
- Published
- 2020
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20. INTEGRATING BIM WITH ON SITE INVESTIGATION FOR SEISMIC VULNERABILITY ASSESSMENT
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Ali Zamani Noori, Farhad Ansari, Valentina Villa, Gian Paolo Cimellaro, Marco Domaneschi, Carlo Caldera, and Sebastiano Marasco
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School building ,BIM ,FEM ,Monitoring ,Seismic vulnerability ,Engineering ,business.industry ,Vulnerability assessment ,business ,Construction engineering - Published
- 2019
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21. Reference free method for real time monitoring of bridge deflections
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Todd Taylor, Farhad Ansari, Karim Helmi, and Ali Zarafshan
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Truck ,Engineering ,business.industry ,Tiltmeter ,Structural engineering ,Finite element method ,Transducer ,Fiber optic sensor ,Deflection (engineering) ,11. Sustainability ,Structural health monitoring ,business ,Strain gauge ,Civil and Structural Engineering - Abstract
Monitoring deflections provides a powerful diagnostic tool for structural health monitoring of bridges. Excessive deflections under service loads may be indicative of structural changes, damage and deterioration. For the real time monitoring of deflections under operating traffic loads, it is often difficult to establish a fixed reference point for displacement transducers either because the bridge crosses over a body of water or a roadway. Moreover, vandalism and environmental conditions disrupt and more than likely alter the fixity of the reference points. The work presented in this study pertains to the development of a method for real time remote monitoring of bridge deflections. From the practical point of view, the primary attribute of the proposed method is its capability for making reference free estimates of bridge deflections. The formulations employ the measured rotations and curvatures of the bridge for this purpose. The feasibility of the approach was tested on two different highway bridges. Both bridges were instrumented with a number of different fiber optic sensors that included tiltmeters and strain gauges. Conventional transducers and displacement measurement devices were also used in parallel in order to evaluate the performance of the proposed method. A series of load tests were conducted at both bridge sites that included use of trucks with known weights. In addition, finite element models were developed and employed for further verification of the proposed approach. Field test measurement results and their correlations with the conventional methods as well as comparison with the finite element models are described in this article. more...
- Published
- 2015
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22. Acousto-opto-mechanical theory for polarization maintaining optical fibers in Brillouin based sensing
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Dewei Meng, Farhad Ansari, Xiaoling Wang, and Tengfei Bao
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Materials science ,Optical fiber ,Physics::Optics ,02 engineering and technology ,01 natural sciences ,law.invention ,010309 optics ,020210 optoelectronics & photonics ,Optics ,Fiber Bragg grating ,Brillouin scattering ,law ,0103 physical sciences ,0202 electrical engineering, electronic engineering, information engineering ,Electrical and Electronic Engineering ,Instrumentation ,business.industry ,Single-mode optical fiber ,Polarization (waves) ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Brillouin zone ,Interferometry ,Wavelength ,Control and Systems Engineering ,Optoelectronics ,business - Abstract
Change in phase or wavelength for interferometric and fiber Bragg Gratings (FBG) based sensors can be described by strain-optic effects. In Brillouin sensors, strain sensitivity need to be expressed in terms of acousto-opto-mechanical properties of fibers. It is then possible to formulate theoretical relationships that lead to the evaluation of strain sensitivities and establishment of gauge factors for Brillouin based sensors. This article reports on the derivation of generalized relationships describing the strain sensitivity in terms of acousto-optic effects in optical fibers. In particular, the formulations correspond to polarization maintaining fibers at various polarization angles with respect to the slow axis of the fiber. The scope of research encompassed theoretical and experimental studies involving both single mode as well as polarization maintaining optical fibers subjected to strain under isothermal conditions. A high resolution BOTDA was employed in the experiments in order to verify the validity of theoretical relationships between strain and Brillouin frequency shifts for different polarization angles. more...
- Published
- 2015
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23. The influence of stress on the quartz birefringent optical filter
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Hua Han, Yong Kong, Todd Taylor, Farhad Ansari, and Yang Liu
- Subjects
Materials science ,Birefringence ,Computer simulation ,business.industry ,Physics::Optics ,02 engineering and technology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,010309 optics ,Stress (mechanics) ,Optical axis ,Wavelength ,020210 optoelectronics & photonics ,Optics ,0103 physical sciences ,0202 electrical engineering, electronic engineering, information engineering ,Electrical and Electronic Engineering ,Optical filter ,business ,Quartz ,Visible spectrum - Abstract
Firstly, based on the elasto-optical effect of quartz crystal, the formula of the transmissivity for the quartz birefringent optical filter (QBOF) applied with the mechanical-stress is derived and analyzed by numerical simulation, which shows that when the stress is applied on the surface of the quartz crystal vertically or parallel to its optical axis, the phase retardation of the quartz crystal will change accordingly, then the output optical spectrum of QBOF applied with stress is measured by Ultra-6600 spectrophotometer, the related experimental results are agreed with the simulation results very well, which show that when the stress is applied on the surface of the quartz crystal, the central wavelength will shift the longer or shorter wavelength according to the direction and the value of the applied stress. At last, a new type of the stress compensation QBOF is proposed, it can offset the change of phase retardation of the quartz crystal caused by the variation of temperature, which will has a certain application for the stable output of optical filter when the environment temperature changes as we believe. more...
- Published
- 2017
- Full Text
- View/download PDF
24. Mechanistic Quantification of Microcracks from Dynamic Distributed Sensing of Strains
- Author
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Saeed Babanajad and Farhad Ansari
- Subjects
Materials science ,business.industry ,Mechanical Engineering ,Structural system ,020101 civil engineering ,02 engineering and technology ,01 natural sciences ,0201 civil engineering ,010309 optics ,Optics ,Mechanics of Materials ,Brillouin scattering ,0103 physical sciences ,Structural health monitoring ,business ,Biological system - Abstract
Monitoring of distributed strains provides important information about the behavior of structural systems. However, detection and quantification of cracks while still at micro size levels w...
- Published
- 2017
- Full Text
- View/download PDF
25. Dynamic Brillouin Scattering–Based Condition Assessment of Cables in Cable-Stayed Bridges
- Author
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Saeed Babanajad, Farhad Ansari, Alice Scarella, Giancarlo Salamone, and Alessandro De Stefano
- Subjects
Engineering ,business.industry ,020101 civil engineering ,02 engineering and technology ,Building and Construction ,Structural engineering ,Condition assessment ,0201 civil engineering ,Deck ,Bridge deck ,020210 optoelectronics & photonics ,Fiber optic sensor ,Brillouin scattering ,0202 electrical engineering, electronic engineering, information engineering ,Time domain ,Cable stayed ,Structural health monitoring ,business ,Civil and Structural Engineering - Abstract
A method for structural health monitoring of cable-stayed bridges based on the dynamic distributed sensing of bridge deck strains is introduced in this article. The objective is to detect the location and the magnitude of the cables that have totally or partially lost their tensile load-carrying capacities. Dynamic sensing provides a realistic approach for condition assessment of the bridge under operational conditions. A Brillouin scattering optical time domain analysis (BOTDA) fiber-optic sensor was used to monitor the distributed strain in the deck of a scaled model cable-stayed bridge in the laboratory. The formulations developed in the present study take advantage of the dynamic distributed sensing capability of the BOTDA in amplitude transfer (AT) mode for the establishment of a relationship between the redistribution of deck strains and the tension loss in the individual cables of cable-stayed bridges. The experimental program involved single cable and multicable damage scenarios. The appli... more...
- Published
- 2017
- Full Text
- View/download PDF
26. Virtual Reference Approach for Dynamic Distributed Sensing of Damage in Large Structures
- Author
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Todd Taylor, Saeed Babanajad, Farhad Ansari, and Yage Zhan
- Subjects
Engineering ,Optical fiber ,business.industry ,Mechanical Engineering ,Structural system ,Reference data (financial markets) ,0211 other engineering and technologies ,Aerospace Engineering ,020101 civil engineering ,Ranging ,02 engineering and technology ,0201 civil engineering ,law.invention ,law ,Brillouin scattering ,Electronic engineering ,General Materials Science ,Structural health monitoring ,State (computer science) ,business ,Beam (structure) ,021101 geological & geomatics engineering ,Civil and Structural Engineering - Abstract
A reference-free damage detection method based on distributed monitoring of strains in large structural systems is introduced. The method employs the dynamic distributed strain data to formulate its own virtual reference state for detection of defect locations. It uses a single line of optical fiber by way of a dynamic pulse-prepump (amplitude transfer) Brillouin scattering technique in order to acquire dynamic distributed strain data. An experimental program was designed to evaluate the performance of the proposed methodology. The experiments involved dynamic tests of a long beam with simulated defects with small opening displacements ranging between 50 and 550 μm. The implications of this approach are significant since it enables the structure to be monitored at any stage during its service life without the need for prior reference data. more...
- Published
- 2017
- Full Text
- View/download PDF
27. A strain monitoring approach for estimating lateral displacements of concrete columns under seismic excitations
- Author
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Farhad Ansari and Asadollah Bassam
- Subjects
Pier ,Engineering ,Discretization ,business.industry ,Mechanical Engineering ,Computation ,02 engineering and technology ,Structural engineering ,021001 nanoscience & nanotechnology ,Curvature ,Displacement (vector) ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Fiber Bragg grating ,Earthquake shaking table ,General Materials Science ,Structural health monitoring ,0210 nano-technology ,business - Abstract
This study describes development of an indirect method for reference-free monitoring of lateral displacements in concrete columns under dynamic loads. The method is independent of the material and section properties of the structure. Therefore, damage due to the change in material and section properties during seismic events does not affect the estimated displacement results. The approach involves discretization of the column elements and placement of strain sensors on opposing sides of the columns for the computation of curvature during the seismic events. Element equivalent force vectors are obtained from the measured strains and subsequently employed for the computation of lateral displacements. Fiber Bragg grating displacement sensors were employed for monitoring the strains. The experimental portion of the research involved shake table tests of a four-span bridge using the recorded ground motions of the 1994 Northridge earthquake. The objective was to verify the accuracy and efficiency of the proposed method by comparing the results with direct displacement measurements. Comparison of the proposed method with the direct measurement of the lateral displacements during the shake table tests indicated reasonable correlation between the computed and direct measurements. more...
- Published
- 2014
- Full Text
- View/download PDF
28. Shear force–based method and application for real-time monitoring of moving vehicle weights on bridges
- Author
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Todd Taylor, Karim Helmi, and Farhad Ansari
- Subjects
Truck ,Influence line ,Engineering ,business.industry ,Mechanical Engineering ,Shear force ,Box girder ,Structural engineering ,computer.software_genre ,law.invention ,Load testing ,Prestressed concrete ,law ,Girder ,General Materials Science ,Weigh in motion ,business ,computer - Abstract
A new approach for monitoring the weight of trucks in motion using the bridge response is introduced in this article. The proposed technique is based on the use of strain rosettes for acquisition of shear strains near bridge supports. Bridge weigh-in-motion monitoring using shear force is a new approach that differs from the prevailing techniques based on the measurement of flexural strains. Formulations are introduced using the shear force response of the bridge in the computation of gross vehicle weights. The method requires truck speeds, influence lines, and shear force responses for the computation of gross vehicle weight. All these are acquired by two sets of rosette sensors attached in series on the webs of bridge girders. An experimental program was designed to evaluate the response of the proposed approach in real-time monitoring of moving truck weights. This was accomplished by instrumentation and load testing of a two-span prestressed concrete box girder bridge by a calibrated truck. Field test results are presented and compared with the actual weight of the calibrated truck. more...
- Published
- 2014
- Full Text
- View/download PDF
29. Theoretical and Experimental Investigations into Crack Detection with BOTDR-Distributed Fiber Optic Sensors
- Author
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Xiaotan Zhang, Jing Zhou, Xin Feng, Changsen Sun, and Farhad Ansari
- Subjects
Materials science ,Optical fiber ,business.industry ,Mechanical Engineering ,Optical time-domain reflectometer ,Classification of discontinuities ,law.invention ,Brillouin zone ,Shear (sheet metal) ,Optics ,Mechanics of Materials ,law ,Fiber optic sensor ,Distortion ,business ,Beam (structure) - Abstract
Development of a model for the analysis of strain transfer mechanism in Brillouin-based sensors with strain singularities is provided in this study. The main objective of the research pertained to the development of a method for accurate detection of cracks and their locations in sensing with Brillouin-based fiber optic distributed sensors. The work involved formulation of a shear lag–based model considering the elastic as well as elastoplastic stages of the fiber optic coating strains. Feasibility of the proposed approach is evaluated through an experimental program. The experimental program involved use of a Brillouin optical time domain reflectometer (BOTDR) for distributed measurement of strain and detection of simulated cracks in a 15-m-long beam. The results indicate that the discontinuities in the strain distribution based on the theoretical analysis provide the means to accurately pinpoint the location of simulated cracks. On the other hand, the distortion effect of the BOTDR system due to... more...
- Published
- 2013
- Full Text
- View/download PDF
30. Field tests and verification of damping calculation methods for operating highway bridges
- Author
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Ali Zarafshan, Farhad Ansari, and Todd Taylor
- Subjects
Engineering ,business.industry ,Structural system ,System identification ,Mechanical engineering ,Box girder ,Structural engineering ,Bridge (nautical) ,Finite element method ,Structural load ,Fiber Bragg grating ,Point (geometry) ,Safety, Risk, Reliability and Quality ,business ,Civil and Structural Engineering - Abstract
Structural damping is an important parameter in system identification and assessment of structural systems. Due to its variable nature, especially in highway bridges, precise estimation of damping poses challenges both from the computational point of views as well as complexity of operations. Survey of technical literature indicates that several methodologies have been developed over the past few decades for the determination of structural damping parameters. The present study determines damping in an operational highway bridge using two approaches, namely, the decay of motion direct measurement and the natural excitation technique. A two-span concrete box girder bridge was instrumented with various types of fiber optic Bragg grating sensors. Series of live load tests were performed on the bridge using a calibrated truck. Estimated damping was implanted in a detailed finite element model of the bridge. Live load on the actual bridge was replicated on the finite element model and the calculated results correlated with measured data at site. more...
- Published
- 2013
- Full Text
- View/download PDF
31. Detection of Tension Loss in Cables of Cable-Stayed Bridges by Distributed Monitoring of Bridge Deck Strains
- Author
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Farhad Ansari, Xiaotan Zhang, Todd Taylor, and Ebrahim Nazarian
- Subjects
Engineering ,business.industry ,Mechanical Engineering ,0211 other engineering and technologies ,Physics::Optics ,020101 civil engineering ,02 engineering and technology ,Building and Construction ,Structural engineering ,Span (engineering) ,Bridge (interpersonal) ,Finite element method ,0201 civil engineering ,Fiber Bragg grating ,Mechanics of Materials ,Fiber optic sensor ,021105 building & construction ,Bending moment ,General Materials Science ,Structural health monitoring ,business ,Strain gauge ,Civil and Structural Engineering - Abstract
Development of a simplified approach for monitoring the cables of cable-stayed bridges is described in this article. The method introduced in this paper uses the distributed measurement of strains along the bridge deck to detect the cables that have totally or partially lost their tensile force. The fundamental principle employed in formulating the method is the interrelationship between the individual cable forces and the bending moment along the bridge span. The proposed method was evaluated through an experimental program that involved fabrication and testing of a reduced scale model of a single plane cable-stayed bridge. Distributed strain along the span length was monitored by a Brillouin Optical (Neubrex, Hyogo, Japan) Time Domain Analysis fiber optic sensor system. Strain gauges, Fiber Bragg Grating sensors (Technica Optical Component, LLC, Beijing, China), and a finite element model of the bridge were employed for evaluating the efficiency of the proposed method. Several different damage c... more...
- Published
- 2016
- Full Text
- View/download PDF
32. Quantitative investigation in distributed sensing of structural defects with Brillouin optical time domain reflectometry
- Author
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Farhad Ansari, Xin Feng, M. Hosein Motamedi, Changsen Sun, and Xiaotan Zhang
- Subjects
Materials science ,business.industry ,Mechanical Engineering ,Optical time-domain reflectometer ,Brillouin zone ,Optics ,Fiber optic sensor ,Brillouin scattering ,General Materials Science ,Structural health monitoring ,Time domain ,business ,Reflectometry ,Image resolution - Abstract
Distributed sensing offers great promise in structural health monitoring of bridges and other types of critical structures. Over the years, a number of different Brillouin scattering–based systems have been developed for distributed sensing, including sensors based on the Brillouin optical time domain reflectometer. This study pertains to the quantitative characterization of Brillouin optical time domain reflectometer–based sensors for monitoring of distributed strains and detection of defects. This study involved experiments involving a 15-m-long beam and simulated defects. In the experiments, the effect of strain localization at the defect sites was masked by the low spatial resolution of the Brillouin optical time domain reflectometer. The Brillouin optical time domain reflectometer–measured response was evaluated by numerical modeling of the beam. Computation of the flexural strains involved a hybrid approach in which the experimentally determined degraded stiffnesses of the defect zones were employed... more...
- Published
- 2012
- Full Text
- View/download PDF
33. Vibration-Based Method and Sensor for Monitoring of Bridge Scour
- Author
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Amirhossein Iranmanesh, Ali Zarafshan, and Farhad Ansari
- Subjects
Pier ,Engineering ,business.industry ,Bridge scour ,Building and Construction ,Structural engineering ,Fundamental frequency ,Open-channel flow ,Vibration ,Flume ,Fiber optic sensor ,Structural health monitoring ,business ,Civil and Structural Engineering - Abstract
Scour is the major cause for many bridge failures and damage to piers and abutments. Scour is not easily discernible because it is hidden under the channel flow. Over the years, a number of sensors have been developed for detection of scour depth. Development, testing, and field implementation of a new and simple type of scour sensor is described in this paper. The scour depth detection concept is based on measuring the fundamental frequency of vibration of a rod embedded in the riverbed. The sensor uses a single fiber-optic Bragg grating (FBG) sensor for transduction of the vibration frequency. The inverse relationship between the fundamental frequency and the length of the sensor rod is used for detection of the scour depth. A computational approach is developed based on the Winkler spring reaction soil model for automated calibration of the scour sensor during installation in the riverbed. The scope of the research included development of the theoretical basis for the sensor, establishment of the computational methodology for detection of the riverbed foundation properties, proof-of-concept laboratory tests, small-scale field verification tests, and installation and remote monitoring of scour in a multispan scour critical bridge in Illinois. The results include laboratory test data from the measurements in soil, simulated scour tests in a hydraulic flume, and real-time data from remote monitoring of scour at the bridge site. more...
- Published
- 2012
- Full Text
- View/download PDF
34. A simple quantitative approach for post earthquake damage assessment of flexure dominant reinforced concrete bridges
- Author
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Amirhossein Iranmanesh, Farhad Ansari, and Asaollah Bassam
- Subjects
Pier ,Engineering ,business.industry ,Computation ,Structural engineering ,Displacement (vector) ,Simple (abstract algebra) ,Fiber optic sensor ,Plastic hinge ,Geotechnical engineering ,Structural health monitoring ,business ,Ductility ,Civil and Structural Engineering - Abstract
Conventional methods for displacement based condition assessment of bridges solely rely on the maximum level of displacements experienced by the piers, and do not take into account the accumulated damage that result from cyclic loading. More advanced approaches take this into account by considering the structural damage as a linear combination of the normalized maximum displacements and hysteretic energy. Computation of the dissipated hysteretic energy requires monitoring of the lateral forces during the seismic events, which are not as practical as monitoring bridge pier deformations. This article reports on the development of a simple damage assessment method that considers the effect of cyclic loading on the state of damage and it is merely based on monitoring the bridge pier deformations. A fiber optic displacement serial array was designed for measuring the crack opening displacement reversals at the plastic hinge areas. more...
- Published
- 2011
- Full Text
- View/download PDF
35. Simplified Technique for Remote Monitoring of Deflection in Arch Structures
- Author
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Farhad Ansari, Chad Fischer, and Iman Talebinejad
- Subjects
Engineering ,business.industry ,Mechanical Engineering ,Vertical deflection ,Structural engineering ,Masonry ,Curvature ,Mechanics of Materials ,Deflection (engineering) ,Nondestructive testing ,Astrophysics::Solar and Stellar Astrophysics ,Vertical displacement ,Arch ,business ,Laser Doppler vibrometer - Abstract
This article describes a simplified technique to measure the vertical deflection of masonry arches in the presence of horizontal movements. One-dimensional laser Doppler vibrometer was utilized to measure the vertical displacement of the arch. A flat steel plate was mounted on the top surface of the arch crown to eliminate the measurement error due to the curvature of the arch. A reflective mirror was employed to guide the emitted laser beam normal to the surface of the steel plate. Vertical displacements recorded by laser Doppler vibrometer were compared to the readings of the mechanical dial gauge. more...
- Published
- 2011
- Full Text
- View/download PDF
36. Damage Assessment and Ductility Evaluation of Post Tensioned Beams with Hybrid FRP Tendons
- Author
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Yujin Liang, Farhad Ansari, and Changsen Sun
- Subjects
Materials science ,business.industry ,Mechanical Engineering ,Glass fiber ,Context (language use) ,Building and Construction ,Structural engineering ,Bending ,Fibre-reinforced plastic ,Flexural strength ,Mechanics of Materials ,Ultimate tensile strength ,Ceramics and Composites ,Composite material ,Deformation (engineering) ,business ,Ductility ,Civil and Structural Engineering - Abstract
The study presented in this article concentrated on investigating the ductility and characterization of damage in concrete beams post tensioned with hybrid carbon-glass fiber-reinforced polymer (HFRP) composites. The investigation included an approach for design of flexural members with HFRP tendons and characterization of damage, load deformation response, ultimate strength, and failure modes. Direct tensile tests of hybrid FRP rods in a previous study had indicated elastoplastic response, enhanced ductility, and increased strain capacity. In this context, the current study focused on design and fabrication of post tensioned beams using glass or steel rebars for partial prestressing. All the beams were tested in flexure under four-point bending configuration. Results of the study are presented in terms of ductility index and enhanced load-deflection response in comparison with the conventional FRP materials. Damage characterization involved evaluating the specific features of the acoustic emissions for d... more...
- Published
- 2011
- Full Text
- View/download PDF
37. Fatigue performance of reinforced concrete beams with externally bonded CFRP reinforcement
- Author
-
Yongtao Dong, Farhad Ansari, and Vistasp M. Karbhari
- Subjects
Cyclic stress ,Materials science ,business.industry ,Mechanical Engineering ,Ocean Engineering ,Building and Construction ,Structural engineering ,Geotechnical Engineering and Engineering Geology ,Reinforced concrete ,Technical literature ,High stress ,Flexural strength ,Fibre optic sensors ,Safety, Risk, Reliability and Quality ,business ,Reinforcement ,Strain gauge ,Civil and Structural Engineering - Abstract
The objective of this paper is to study the flexural performance of reinforced concrete (RC) beams strengthened with externally bonded carbon fibre reinforced polymer (CFRP) fabrics under fatigue loadings, including load, which will produce high stress levels in the materials. The crack development and the stress change in the steel and the CFRP were monitored by strain gauges and fibre optic sensors in the process of the fatigue tests, and the failure mechanisms were compared with that of statically loaded similar beams. The behaviour of the S–N (cyclic stress versus numbers of cycle to failure) data from the current tests and the available technical literature is analysed and compared with existing fatigue design rules for un-strengthened RC beams using ACI 215 guidelines and AASHTO specifications. more...
- Published
- 2011
- Full Text
- View/download PDF
38. Numerical Evaluation of Vibration-Based Methods for Damage Assessment of Cable-Stayed Bridges
- Author
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Iman Talebinejad, Farhad Ansari, and Chad Fischer
- Subjects
Engineering ,business.industry ,Modal analysis ,Numerical analysis ,Structural engineering ,Accelerometer ,Computer Graphics and Computer-Aided Design ,Bridge (nautical) ,Finite element method ,Computer Science Applications ,Vibration ,Modal ,Computational Theory and Mathematics ,Structural health monitoring ,business ,Civil and Structural Engineering - Abstract
This study investigated a number of different damage detection algorithms for structural health monitoring of a typical cable-stayed bridge. The Bayview Bridge, a cable-stayed bridge in Quincy, Illinois, was selected for the study. The focus was in comparing the viability of simplified techniques for practical applications. Accordingly, the numerical analysis involved development of a precise linear elastic finite element model (FEM) to simulate various structural health monitoring test scenarios with accelerometers. The Effective Independence Method was employed to locate the best distribution of the accelerometers along the length of the bridge. The simulated accelerometer data based on the FEM analysis was employed for the evaluation of the four damage identification methods investigated here. These methods included the Enhanced Coordinate Modal Assurance Criterion, Damage Index Method, Mode Shape Curvature Method, and Modal Flexibility Index Method. Some of these methods had been previously applied only to a number of specific bridges. However, the investigation here provides the relative merits and shortcomings of the damage detection methods in long-span cable-stayed bridges. more...
- Published
- 2010
- Full Text
- View/download PDF
39. Serially multiplexed FBG accelerometer for structural health monitoring of bridges
- Author
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Chad Fischer, Farhad Ansari, and Iman Talebinejad
- Subjects
Engineering ,Optical fiber ,business.industry ,Physics::Optics ,Accelerometer ,Multiplexing ,Computer Science Applications ,law.invention ,Vibration ,Acceleration ,Fiber Bragg grating ,Control and Systems Engineering ,law ,Electronic engineering ,Structural health monitoring ,Electrical and Electronic Engineering ,business ,Frequency domain decomposition - Abstract
This article describes the development of a fiber optic accelerometer based on Fiber Bragg Gratings (FBG). The accelerometer utilizes the stiffness of the optical fiber and a lumped mass in the design. Acceleration is measured by the FBG in response to the vibration of the fiber optic mass system. The wavelength shift of FBG is proportional to the change in acceleration, and the gauge factor pertains to the shift in wavelength as a function of acceleration. Low frequency version of the accelerometer was developed for applications in monitoring bridges. The accelerometer was first evaluated in laboratory settings and then employed in a demonstration project for condition assessment of a bridge. Laboratory experiments involved evaluation of the sensitivity and resolution of measurements under a series of low frequency low amplitude conditions. The main feature of this accelerometer is single channel multiplexing capability rendering the system highly practical for application in condition assessment of bridges. This feature of the accelerometer was evaluated by using the system during ambient vibration tests of a bridge. The Frequency Domain Decomposition method was employed to identify the mode shapes and natural frequencies of the bridge. Results were compared with the data acquired from the conventional accelerometers. more...
- Published
- 2009
- Full Text
- View/download PDF
40. Post earthquake performance monitoring of a typical highway overpass bridge
- Author
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Asadollah Bassam, Amirhossein Iranmanesh, and Farhad Ansari
- Subjects
Engineering ,business.industry ,Seismic loading ,Structural engineering ,Bridge (interpersonal) ,Physics::Geophysics ,Computer Science Applications ,Deck ,OpenSees ,Control and Systems Engineering ,Earthquake shaking table ,Geotechnical engineering ,Electrical and Electronic Engineering ,Seismic risk ,business ,Size effect on structural strength ,Stiffness matrix - Abstract
Bridges form crucial links in the transportation network especially in high seismic risk regions. This research aims to provide a quantitative methodology for post-earthquake performance evaluation of the bridges. The experimental portion of the research involved shake table tests of a 4-span bridge which was subjected to progressively increasing amplitudes of seismic motions recorded from the Northridge earthquake. As part of this project, a high resolution long gauge fiber optic displacement sensor was developed for post-seismic evaluation of damage in the columns of the bridge. The nonlinear finite element model was developed using Opensees program to simulate the response of the bridge and the abutments to the seismic loads. The model was modified to predict the bent displacements of the bridge commensurate with the measured bent displacements obtained from experimental analysis results. Following seismic events, the tangential stiffness matrix of the whole structure is reduced due to reduction in structural strength. The nonlinear static push over analysis using current damaged stiffness matrix provides the longitudinal and transverse ultimate capacities of the bridge. Capacity loss in the transverse and longitudinal directions following the seismic events was correlated to the maximum displacements of the deck recorded during the events. more...
- Published
- 2009
- Full Text
- View/download PDF
41. Structural health monitoring with fiber optic sensors
- Author
-
Farhad Ansari
- Subjects
Engineering ,Optical fiber ,business.industry ,Mechanical Engineering ,Survivability ,Structural engineering ,law.invention ,Mechanical system ,Reliability (semiconductor) ,Fiber optic sensor ,law ,Transfer mechanism ,Systems engineering ,Structural health monitoring ,business - Abstract
Optical fiber sensors have been successfully implemented in aeronautics, mechanical systems, and medical applications. Civil structures pose further challenges in monitoring mainly due to their large dimensions, diversity and heterogeneity of materials involved, and hostile construction environment. This article provides a summary of basic principles pertaining to practical health monitoring of civil engineering structures with optical fiber sensors. The issues discussed include basic sensor principles, strain transfer mechanism, sensor packaging, sensor placement in construction environment, and reliability and survivability of the sensors. more...
- Published
- 2009
- Full Text
- View/download PDF
42. Measurement of creep of optical fiber by a low coherent white light double interferometer system
- Author
-
ZhiHong Xu and Farhad Ansari
- Subjects
Materials science ,Optical fiber ,business.industry ,Physics::Optics ,Polarization-maintaining optical fiber ,Optical time-domain reflectometer ,Graded-index fiber ,law.invention ,Optics ,Fiber Bragg grating ,law ,Fiber optic sensor ,Dispersion-shifted fiber ,business ,Plastic optical fiber - Abstract
The creep properties of optical fiber used in fiber optical sensors were studied in this paper. A low coherent white light double interferometer system was designed and calibrated and the creep deformations of optical fibers under static and cyclic loadings were measured with this device. The research results showed that polymer coated optical fibers crept at the beginning when they were under static or cyclic load. As the number of the cyclic loading or the static loading times increased the creep tended to stop. Thus to ensure that the optical fiber keeps pre-stress for long time in pressure transducer, it is recommended that the optical fiber should be tensioned cyclically before being fixed into the sensor device. more...
- Published
- 2009
- Full Text
- View/download PDF
43. COMPUTER-ASSISTED INSTRUMENTED IMPACT TESTING OF REINFORCED CONCRETE
- Author
-
Farhad Ansari and S. X. Yang
- Subjects
Impact testing ,Engineering ,Mechanics of Materials ,business.industry ,Mechanical Engineering ,Structural engineering ,Composite material ,business ,Reinforced concrete - Published
- 2008
- Full Text
- View/download PDF
44. Generalized Method and Monitoring Technique for Shear-Strain-Based Bridge Weigh-in-Motion
- Author
-
Tengfei Bao, Farhad Ansari, Saeed Babanajad, and Todd Taylor
- Subjects
Influence line ,Engineering ,business.industry ,Shear force ,020101 civil engineering ,02 engineering and technology ,Building and Construction ,Structural engineering ,Span (engineering) ,0201 civil engineering ,law.invention ,Axle ,020303 mechanical engineering & transports ,Prestressed concrete ,0203 mechanical engineering ,Structural load ,law ,Weigh in motion ,Structural health monitoring ,business ,Civil and Structural Engineering - Abstract
Development and testing of a new type of bridge weigh-in-motion system (BWIM) based on the measurement of shear forces near the supports of the bridges is described. The proposed system is applicable to both determinate as well as indeterminate bridges. Fiber-optic Bragg grating rosette sensors were used in this approach. Formulations are based on the establishment of shear influence lines in terms of axle weights and spacings. The system further involves calibration for the estimation of a bridge parameter α, which is a function of the cross-sectional and material properties of the bridge. Three different bridges, one box-girder prestressed concrete bridge and two concrete-slab-on-steel-girder bridges with different span lengths, were instrumented for the evaluation of the proposed BWIM system. Field implementation involved a series of truck runs for calibration and evaluation of the BWIM system. Measured and actual truck-axle weights, spacings, and axle speeds as well as the gross vehicle weight... more...
- Published
- 2016
- Full Text
- View/download PDF
45. Post-seismic Structural Health Monitoring of a Column Subjected to Near Source Ground Motions
- Author
-
Farhad Ansari and Seyed Asadollah Bassam
- Subjects
Earthquake engineering ,Engineering ,business.industry ,Mechanical Engineering ,Modal analysis ,Structural engineering ,Dynamic load testing ,Vibration ,Fiber optic sensor ,Earthquake shaking table ,General Materials Science ,Structural health monitoring ,business ,Shape analysis (digital geometry) - Abstract
This study reports on the results acquired from shaking table tests of a column subjected to progressively increasing amplitudes of seismic motions recorded during the Northridge earthquake. Scope of the investigation includes application and evaluation of deterministic structural health monitoring methods to assess the post-seismic conditions following application of the various amplitudes of earthquake motions. Results from this study demonstrate the applicability of specially designed surface-adhered fiber optic sensors for detecting the formation and the progression of cracks subjected to reverse dynamic loads, as well as application of various SHM techniques for evaluation of damage. The range of damage identification methods evaluated comprises of simple frequency and damping analysis of the column under free vibrations, and modal analysis techniques including curvature mode shapes. The concept of strain mode shape analysis, which was previously established for dynamic analysis of structures, is also introduced here for damage identification. Evaluation of the SHM techniques involves efficiency in terms of the number of sensors required to investigate the progression of damage, and resolution in terms of damage identification both in terms of location as well as the state of the damage. more...
- Published
- 2007
- Full Text
- View/download PDF
46. Practical Implementation of Optical Fiber Sensors in Civil Structural Health Monitoring
- Author
-
Farhad Ansari
- Subjects
Engineering ,Optical fiber ,business.industry ,Mechanical Engineering ,Structural system ,Survivability ,law.invention ,Mechanical system ,law ,Fiber optic sensor ,Systems engineering ,Key (cryptography) ,General Materials Science ,Structural health monitoring ,business ,Telecommunications ,Reliability (statistics) - Abstract
Implementation of successful civil structural health monitoring strategies requires selection and placement of sensors suitable for measurement of key parameters that influence the performance and health of the structural system. Optical fiber sensors have been successfully implemented in aeronautics, mechanical systems, and medical applications. Civil structures pose further challenges in monitoring mainly due to their large dimensions, diversity as well as heterogeneity of materials involved, and hostile construction environment. This article provides a summary of basic principles pertaining to practical health monitoring of civil engineering structures with optical fiber sensors. The issues discussed include basic sensor principles, strain transfer mechanism, sensor packaging, sensor placement in construction environment, and reliability and survivability of the sensors. more...
- Published
- 2007
- Full Text
- View/download PDF
47. Monitoring of Bond in FRP Retrofitted Concrete Structures
- Author
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Yang Zhao, Adam G. Tennant, Ming Ming Zhao, Yongtao Dong, and Farhad Ansari
- Subjects
Materials science ,Brittleness ,business.industry ,Mechanical Engineering ,Bond ,General Materials Science ,Structural engineering ,Fibre-reinforced plastic ,Composite material ,Reinforced concrete ,business ,Concrete cover - Abstract
Debonding failure of the concrete cover in reinforced concrete beams retrofitted with fiber reinforced polymer (FRP) composites is a brittle phenomenon which in most cases occurs in an abrupt manner. A complete understanding of bond requires information about the relationship between the local bond stress and slip. Bond-slip defines the constitutive relationship of the interface, and it provides means for computation of ultimate strength and distribution of the bond stress. For FRP composites interface slip is very small even at the ultimate stage prior to failure. For this reason, the study of local bond in the earlier studies did not include slip. This article presents a fiber optic based method for measurement of local slip at the interface between concrete and FRP as well as for prediction of bond failure in reinforced concrete members. Since bond failure in FRP retrofitted concrete is a brittle phenomenon, development of effective means to predict the failure prior to occurrence plays an important role in structural health monitoring of such structures. Therefore, the scope of the study includes two types of tests, namely pull out tests and beam flexure tests. In general, the measured interface slip between concrete substrate and FRP at ultimate load stage is more...
- Published
- 2007
- Full Text
- View/download PDF
48. Monitoring with fiber optic sensors of a cable-stayed bridge in the Port of Venice
- Author
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Farhad Ansari, Luca Massimo Giacosa, and A De Stefano
- Subjects
Engineering ,business.industry ,Fiber optic sensor ,Structural engineering ,Cable stayed ,Structural health monitoring ,business - Published
- 2015
- Full Text
- View/download PDF
49. Crack tip opening displacement in micro-cracked concrete by an embedded optical fiber sensor
- Author
-
Zhijun Zhang and Farhad Ansari
- Subjects
Engineering ,Multi-mode optical fiber ,Optical fiber ,business.industry ,Mechanical Engineering ,Crack tip opening displacement ,Displacement (vector) ,law.invention ,Speckle pattern ,Light intensity ,Mechanics of Materials ,Fiber optic sensor ,law ,Fracture (geology) ,General Materials Science ,Composite material ,business - Abstract
Crack tip opening displacement (CTOD) is an important parameter that is often employed in characterization of fracture in engineering materials. Due to inherent difficulties in direct determination of CTOD, the crack mouth opening displacement (CMOD) has been measured during fracture tests of concrete beams and then related to CTOD. Analytical schemes are used for the determination of CTOD from the measured crack mouth opening displacements, which leads to the determination of other fracture parameters of importance. The research presented here describes development of an experimental technique for direct determination of CTOD based on embedded fiber optic sensors. The transduction mechanism is based on the correlation between the applied strain and the light intensity variation of speckle patterns generated at the output end of the multimode optical fiber due to mode redistribution.The measured displacements, CTOD, and CMOD, are compared and the validity of analytical schemes in estimation of CTOD is evaluated. more...
- Published
- 2005
- Full Text
- View/download PDF
50. Fiber optic health monitoring of civil structures using long gage and acoustic sensors
- Author
-
Farhad Ansari
- Subjects
Engineering ,Optical fiber ,business.industry ,Acoustics ,Structural system ,Condensed Matter Physics ,Multiplexing ,Atomic and Molecular Physics, and Optics ,law.invention ,Optics ,Fiber Bragg grating ,Mechanics of Materials ,law ,Signal Processing ,General Materials Science ,Structural health monitoring ,Electrical and Electronic Engineering ,business ,Civil and Structural Engineering - Abstract
Structural health monitoring with optical fibers provides practical sensing capabilities in many applications including in aeronautics and mechanical structures. A variety of optical fiber sensors have been used including Bragg gratings, intensity or amplitude sensors, and Fabry–Perot ones. Civil structures pose further challenges in monitoring mainly due to their large dimensions, diversity as well as heterogeneity of materials involved, and hostile construction environment. Monitoring of strains, deformations, and deflections provides clues essential for evaluation of design parameters and behavior under service loads. Long gage distributed or multiplexed sensors are excellent candidates for such applications. On the other hand, detection of structural damage and anomalies such as cracking in concrete, splintering of fibers in composites, and fracturing of welds and connections are best accomplished by acoustic sensors. This paper describes principles involved in serial multiplexing of two kinds of optical fibers, namely long gage and acoustic sensors. Both sensor types offer promise in structural health monitoring of large civil structural systems. Representative examples are introduced and described in detail. more...
- Published
- 2005
- Full Text
- View/download PDF
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