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Öğe Civil infrastructure monitoring with quantitative acoustic emission methods(International Society for Structural Health Monitoring of Intelligent Infrastructure, ISHMII, 2021) Alver N.; Ozevin D.Acoustic emission (AE) method has been widely used for investigating damage in materials and structures. It allows monitoring the damage progress within the material during loading. In conventional parameter-based AE analysis, only AE parameters are recorded and analyzed to clarify fracture behavior in materials. Quantitative analysis methods allow for a comprehensive fracture characterization of materials in which waveform itself is stored and analyzed. Large number of research and case studies reveal that for civil infrastructure monitoring, parameter-based analyses of AE are preferred compared with quantitative analyses. This is because, concrete, being mostly used material for constructing civil structures, has a very complex nature and without proper and adequate instrumentation, set-up and algorithms, it is difficult to properly characterize fracture mechanisms with quantitative techniques. Still, it is very important to obtain these fracture characteristics such as the time crack developed, the location of the crack and also the type of the crack to better understand the fracture behavior of a structural element under consideration such as how this element behaves under certain load levels and what leads to its failure. There have been numerous challenges and solutions in application of quantitative AE techniques to civil infrastructure from reliable AE source localization to defect type identification. In this study, these applications and solution methods have been reviewed thoroughly and presented. © 2021 International Conference on Structural Health Monitoring of Intelligent Infrastructure: Transferring Research into Practice, SHMII. All rights reserved.Öğe Cross-sectional visualization of defects by SIBIE(Springer Netherlands, 2016) Watanabe T.; Alver N.; Ohtsu M.For nondestructive evaluation (NDE) of concrete structures, the impact-echo method has been successfully applied to locate defects and voids in concrete. To compensate the difficulty in selecting the resonant frequency and to visually locate a defect, an imaging procedure named SIBIE (Stack Imaging of spectral amplitude Based on Impact-Echo) has been developed. This is an imaging technique for visualizing defects of which locations are known or identified. Following the basic concept and procedure, applications to concrete structures are discussed. The presence of the ungrouted duct can be visually identified by the SIBIE procedure in both the cases of plastic sheath and metal sheath. In addition, the depth of the surface crack is visually evaluated. © RILEM 2016.Öğe Evaluation of acoustic emission activities in a steel fiber reinforced concrete beam by Ib value analysis [Çelik lifli betonarme kirişte akustik emisyon aktivitelerinin Ib değeri analizi ile değerlendirilmesi](Gazi Universitesi Muhendislik-Mimarlik, 2019) Tayfur S.; Alver N.; Saatcı S.There are numerous nondestructive testing methods that are used to determine damages within structures. Acoustic Emission (AE), being one of these methods makes it possible to obtain significant pieces of information such as origin time, location and type of damage formed in a material during loading by analyzing AE data using various algorithms. Ib value analysis is one of these algorithms which is based on AE signal and this analysis enables to have information on formation of new cracks or propagation of existing cracks by scaling the magnitude of AE activities. In this study, in order to investigate effect of the steel fiber in concrete matrix on Ib value, two reinforced concrete beams were tested under simple bending while one of them was the reference. Afterwards, AE parameters obtained were analyzed, Ib value analyses were applied to amplitude values and these parameters were associated to each other. Furthermore, effect of steel fiber existence on behavior of the beam and distribution of Ib value were examined. © 2019 Gazi Universitesi Muhendislik-Mimarlik. All rights reserved.Öğe Fracture mechanism of CFRP-strengthened RC beam identified by AE-SIGMA(CRC Press/Balkema, 2016) Alver N.; Tanarslan H.M.; Sülün Ö.Y.; Ercan E.Externally bonded Carbon Fiber-Reinforced Polymer (CFRP) has been used widely to repair and/or strengthen structures that are deficient in strength. Even though strengthening with CFRP has many advantages, previous studies have shown that sudden failure due to debonding is the major problem for FRP-strengthened RC beams. Thus, it is important to clarify failure mechanisms of a strengthened RC beam with CFRP to hinder this problem. In this study, AE-SiGMA method is applied for determination of cracking development mechanism of RC beams strengthened with CFRP in different widths. In the experimental work, specimens strengthened with CFRP strips were tested under cyclic loading along with AE tests. It was found out that increasing the strip width does not enhance the behaviour. © 2016 Taylor & Francis Group, London.Öğe Health monitoring of civil infrastructure and materials(ScientificWorld Ltd., 2014) Aggelis D.G.; Alver N.; Chai H.K.[No abstract available]Öğe Identifying the effect of CFRP application type on behavior of CFRP-strengthened beams by acoustic emission(DEStech Publications, 2017) Alver N.; Tayfur S.; Tanarslan H.M.Strengthening structures using CFRP (Carbon Fiber Reinforced Polymer) strips is a widely used method because of superior mechanical properties of CFRP. Along with the overall impact of the FRP strengthening, FRP application type is one such important parameter that directly affects the strengthened beam behavior. FRP can be applied in a number of different ways. FRP sheets, either full wraps or strips are the mostly preferred methods for strengthening in recent years. These methods have more or less advantages according to each other. In other words, CFRP application influences the strengthened beam behavior since application type has a direct impact on the failure mechanism. In this study, it was aimed to identify the effect of CFRP application type on behavior of reinforced concrete (RC) beams. For this purpose, CFRP-strengthened RC beams, which were strengthened by different application types such as side-bonded and U-jacketed CFRP sheets, were tested under cyclic loading and monitored by Acoustic Emission (AE) technique. AE data obtained from the tests were processed by parameter and SiGMA analyses. Crack locations, types and orientations were determined and were compared with mechanical results. Thus, failure mechanisms of the specimens were evaluated and effects and discrimination of CFRP application type on the fracture mechanism were revealed.Öğe Imaging of voids in concrete by impact-echo and ultrasonic-echo methods [Betondaki boşlukların darbe-eko ve ultrasonik-eko yöntemleri ile görüntülenmesi](Gazi Universitesi Muhendislik-Mimarlik, 2018) Tayfur S.; Alver N.Impact-echo (IE) and ultrasonic-echo (UE) are widely used elastic wave methods to determine voids in concrete and have successful applications in the field. However, because in most cases it is difficult to interpret the results, researchers have been studying on to develop imaging algorithms. In this study, SIBIE (Stack Imaging of Spectral Amplitudes Based on IE) and SAFT (Synthetic Aperture Focusing Technique) algorithms were used in order to evaluate voids within concrete blocks. For this purpose, concrete blocks containing post-tensioning ducts that include voids were produced and IE and UE tests were carried out to locate the voids. Moreover, apart from the other studies in literature, effect of thickness of the metal ducts on phase change of the ultrasonic signal was determined. As a result of the study, along with successful void visualization, material characterization by means of acoustic impedance characteristics of air and steel was made. © 2018 Gazi Universitesi Muhendislik-Mimarlik. All rights reserved.Öğe Influences of nano-clay amount on flexure behavior of concrete identified by acoustic emission(Pontificia Universidad Catolica de Chile, Escuela de Construccion Civil, 2024) Tayfur S.; Üna H.Y.; Alver N.; Pekbey Y.Nano-modification is an effective method currently used to improve mechanical properties of concrete by adding various nanomaterials. The results obtained from previous studies demonstrate that presence of these particles has positive effects on both mechanical and durability performances of concrete. However, while the existing studies investigate the state of resistance, revealing progressive failure mechanism of nano-particle added concrete under loading is a significant subject. In this regard, Acoustic Emission (AE) method is useful for identification of invisible damage progress by means of basic phenomenon defined as release of energy due to a fracture and propagation of it as elastic waves in a stressed medium. Apart from the existing studies in the literature, this paper is focused on investigation of the influences of nano-clay on mechanical and failure behaviors of concrete by AE. For this purpose, a plain and three different concrete mixtures including 1%, 3% and 5% nano-clay (NC) of cement weight were prepared. 100x100x600 mm beam specimens were produced from these mixtures and were tested under three-point-bending. Furthermore, to reveal invisible failure mechanisms of the specimens, all tests were simultaneously monitored with AE method. The results reveal that presence of nanoclay increases the load capacity and ductility of the concrete specimens which is also confirmed by AE results, as more amount of micro-scale events are obtained. © 2024 Tayfur, S., Yavuz, H., Alver, N., Pekbey, Y. This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivatives 4.0 International LicenseÖğe A modified fiber-reinforced plastics concrete interface bond-slip law for shear-strengthened RC elements under cyclic loading(John Wiley and Sons Inc., 2016) Selman E.; Alver N.The objective of this article is to realistically analyze fiber-reinforced plastics (FRP) retrofitted reinforced concrete structures under cyclic loading taking into account FRP–concrete bond-slip law with cyclic bond degradation. In literature, even though numerous studies have been conducted in FRP–concrete interface bond-slip modeling under cyclic loads, a small number of them consider the influence of cyclic degradation on FRP–concrete interface bond behavior. Within this framework, the bond-slip law for carbon fiber-reinforced plastics–concrete interface is revised by utilizing Harajli's and Ko-Sato's approaches. The procedure is distinct from others because it develops existing deficiencies of these approaches, whereas a more reliable modeling process is proposed for use in practice. Conventional bond-slip law of Lu et al. is compared with this interface relationship stated in this investigation and the difference is clearly shown in terms of structural parameters. Experimental tests are conducted at the same time for verification. It is proved that cyclic bond degradation affects the interface behavior; thus, the structural response cannot be omitted in structural evaluations. Structural performance measures are obtained in good agreement for each level of cycles. The technique proposed clearly exhibits structural response difference between monotonic and cyclic loadings while good agreement is reached with experimental results. POLYM. COMPOS., 37:3373–3383, 2016. © 2015 Society of Plastics Engineers. © 2015 Society of Plastics EngineersÖğe Non-destructive evaluation for corrosion monitoring in concrete: A review and capability of acoustic emission technique(MDPI AG, 2015) Zaki A.; Chai H.K.; Aggelis D.G.; Alver N.Corrosion of reinforced concrete (RC) structures has been one of the major causes of structural failure. Early detection of the corrosion process could help limit the location and the extent of necessary repairs or replacement, as well as reduce the cost associated with rehabilitation work. Non-destructive testing (NDT) methods have been found to be useful for in-situ evaluation of steel corrosion in RC, where the effect of steel corrosion and the integrity of the concrete structure can be assessed effectively. A complementary study of NDT methods for the investigation of corrosion is presented here. In this paper, acoustic emission (AE) effectively detects the corrosion of concrete structures at an early stage. The capability of the AE technique to detect corrosion occurring in real-time makes it a strong candidate for serving as an efficient NDT method, giving it an advantage over other NDT methods. © 2015 by the authors; licensee MDPI, Basel, Switzerland.Öğe Nondestructive evaluation of surface crack depth in concrete(2013) Alver N.; Ohtsu M.Subsurface damages in concrete may cause considerable durability loss in the structure since they are not visible from the surface and let water and other chemicals to penetrate into the structure and cause reinforcement corrosion. Ultrasonic methods have been widely applied for defect detection in concrete, however, there are not many applications of the method found in literature for subsurface damage identification. Specifically, when the damage is deeper considering the distance from the top surface. Therefore, in this study concrete blocks including subsurface cracks with different depths as well as a sound concrete block were tested by applying ultrasound. Wave parameters such as velocity and attenuation for each case were evaluated. Rayleigh wave and longitudinal wave velocities do not change for different subsurface crack depths. Even though, wave energy attenuates more in case of a shallower crack, it is difficult to correlate the attenuation rate with crack depth. Still, attenuation rate is an indicative parameter for subsurface damage identification. Numerical results obtained by Boundary Element Method (BEM) analysis are in good agreement with experimental ones. Stack imaging procedure applied to ultrasonic echo data is used as a complementary technique for subsurface crack depth identification. Reflection at the crack depth can be clearly identified. © The Society for Experimental Mechanics, Inc. 2013.Öğe Study of fracture evolution in FRP-strengthened reinforced concrete beam under cyclic load by acoustic emission technique: An integrated mechanical-acoustic energy approach(Elsevier Ltd, 2015) Selman E.; Ghiami A.; Alver N.Abstract Acoustic emission (AE) is an effective tool to evaluate the damage progression qualitatively and it can be used to assess important damage mechanism points of a structural element during loading. These assessments are made either by signal-based analyses or parameter-based analyses. In order to investigate the behavior of a reinforced concrete element strengthened with carbon fiber reinforced polymers (CFRP), both mechanical and acoustic information have been considered independently in several studies. However, it is important to combine both the mechanical and acoustic energy information to make a more comprehensive damage characterization. In order to perform a deeper analysis of FRP-strengthened reinforced concrete structure's damage evolution, a unitless function so called "sentry" that combines both the mechanical and acoustic energy information is employed in this study. This function is expressed in the terms of the logarithmic ratio of the strain energy (ES) and the acoustic energy (EAC). According to the results obtained in this study, sentry function is proved to be successful and efficient method in CFRP-strengthened reinforced concrete elements that can be used in observing their structural failure mechanism for realistic assessments. © 2015 Elsevier Ltd.
