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Dissertations / Theses on the topic 'Defects in concrete'
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1
Priyosulistyo, Henricus. "Detection of defects in concrete structures using vibration technique." Thesis, University of Strathclyde, 1992. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21555.
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This thesis investigates the dynamic behaviour of reinforced concrete beams as they are loaded to failure. Four beams have been investigated. Two types of crack pattern and two types or reinforcement pattern were the main variable parameters. Partially bonded reinforcement as artificially created (by greasing the bars) and positioned at the center third span in two of the four beams investigated. The remaining two beams had conventional bonded reinforcement. Flexural and diagonal splitting patterns were created by loading mechanisms individually applied on two beams of each type of reinforcement. Stage by stage application of static loadings was used. Steady state vibration tests were applied at prior to loadings the beams and at several load stages as gradually increasing defects occurred. There are four parts to this investigation and these are presented in this thesis. The first part investigates the accuracy of several techniques dealing with signal parameters from a digital response spectrum in the signal processing. A logic geometry was developed and was applied on the line spectra of the response spectrum. Numerical evaluation found that the error induced in the proposed technique decreased exponentially with increasing numbers of cycles. A maximum of 0.17% errors may exist when examining 100 cycles of the frequency of interest. A regression analysis was used to achieve further accuracy of the results. The second part investigates the jump phenomenon of mechanical exciters and the sharp drop phenomenon of magnetic exciters. Both of which may confuse the analysis of structural dynamic behaviour. By accounting for the stiffness of the magnetic field of the magnetic exciter in a mathematical model, the jump phenomena was shown to be due to the effect of the reflected force in the excited structure. Practical equations were also proposed to relate absolute to relative parameters. The third part of the thesis concerns the algorithms required in filter processing and includes the development of a computer solution. Two algorithms were developed to obtain coefficients of a polynomial equation which was set up from elementary equations and from a rational function respectively. The algorithms were simple and easy to program. The last part of the thesis discusses the detection of flexural and diagonal splitting defects and non-linear behaviour of the beams during the vibration tests. Static and dynamic comparisons are also discussed. Based on the characteristics of the polar diagrams it was found that several possible types of non-linear damping were demonstrated in the experiments. The typical viscous and non-linear higher polynomial damping existed mostly in the models although the crack pattern and intensity of cracks contributed to changes in the type of damping. In addition the beam models in almost all conditions showed non-linear soft spring behaviour. Diagonal splitting crack patterns can be idenuried from a small decrease of resonant frequency and from the sharp drop of resonant amplitude. The presence of single deep cracks greatly reduced the stiffness. The experiments show that a sharp decrease of resonant frequency indicates that a large amount of residual strain exists. It is concluded that defects of the reinforced concrete beams can be identified from the changes of the dynamic parameters using the proper digital signal analyses. The jump phenomenon is shown to be due to the effect of the reflected force on the moving exciter mass rather than due to the presence of the non-linear soft spring system.
2
Xia, Xiahua. "Acoustic resonance spectroscopy (ARS) of concrete components." Thesis, King's College London (University of London), 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267620.
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Schurr, Dennis Patrick. "Monitoring damage in concrete using diffuse ultrasonic coda wave interferometry." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37237.
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The prevalence of concrete and cement-based materials in the civil infrastructure
plus the risk of failure makes structural health monitoring an important issue in the
understanding of the complete life cycle of civil structures. Correspondingly, the
field of nondestructive evaluation (NDE) has been maturing and now concentrates
on the detection of flaws and defects, as well as material damage in early stages of
degradation.
This defect detection is typically usually done by looking at the impulse response
of the medium in question such as a cement-based material. The impulse response
of a solid can be used to image a complex medium. Classically, the waveform is
obtained by an active setup: an ultrasonic signal is generated at one location and
recorded at another location. The waveform obtained from imaging can be used to
quantitatively characterize the medium, for example by calculating the material's
diffusivity coefficient or dissipation rate.
In recent years, a different monitoring technique has been developed in seismology
to measure the velocity of different kinds of waves, the Coda Wave Interferometry
(CWI). In this CWI technique, the main focus is given to the late part of the recorded
waveform, the coda. CWI is now successfully used in seismology and acoustics.
In the current research, CWI is applied on concrete in different damage states
to develop basic knowledge of the behavior of the wave velocity, and how it can be
used to characterize cement-based materials. By comparing two impulse responses,
the relative velocity change between the two impulse responses is used to characterize
damage. Because of the stress-dependency of the velocity change, the calculations can also be used to directly calculate the Murnaghan's and Lam´e's coefficients. The
newer technique of CWI is applied - the Stretching Technique (ST) [27]. The first goal
of this research is to establish the viability of using CWI in cement-based materials.
Next, we use the ST in the application of stress as we compress concrete samples for
the detection of thermal damage, ASR-damage and mechanical softening.
4
Chen, Justin Gejune. "Detection of defects in FRP-reinforced concrete with the acoustic-laser vibrometry method." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/79423.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 165-168).
Fiber-reinforced polymer (FRP) strengthening and retrofitting of concrete structural elements has become increasingly popular for civil infrastructure systems. When defects occur in FRP-reinforced concrete elements at the FRP-concrete interface, such as voids or delamination, FRP obscures the defect such that visual detection may not be possible. Most currently available non-destructive testing (NDT) methods rely on physical contact; an NDT method that is capable of remotely assessing damage would be greatly advantageous. A novel approach called the acoustic-laser vibrometry method which is capable of remote assessment of damage in FRP-reinforced concrete, is investigated in this thesis. It exploits the fact that areas where the FRP has debonded from concrete will vibrate excessively compared to intact material. In order to investigate this method, a laboratory system consisting of a commercial laser vibrometer system and conventional loudspeaker was used to perform tests with fabricated FRP-reinforced concrete specimens. The measurement results in the form of resonant frequencies were compared to those determined from theoretical and finite element defect models. With a series of measurements the vibrational mode shapes of defects and extent of the damage were imaged. The feasibility of the method was determined through a series of parametric studies, including sound pressure level (SPL), defect size, laser signal level, and angle of incidence. A preliminary Receiver Operating Characteristic (ROC) curve was determined for the method, and future work involving the acoustic-laser vibrometry method is proposed.
by Justin Gejune Chen.
S.M.
5
Moodi, Faramarz. "Development of a knowledge-based system for the repair and maintenance of concrete structures." Thesis, University of Newcastle Upon Tyne, 2001. http://hdl.handle.net/10443/481.
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Information Technology (IT) can exploit strategic opportunities for new ways of facilitating information and data exchange and the exchange of expert and specialist opinions in any field of engineering. Knowledge-Based Systems are sophisticated computer programs which store expert knowledge on specific subject and are applied to a broad range of engineering problems. Integrated Database applications have facilitated the essential capability of storing data to overcome an increasing information malaise. Integrating these areas of Information Technology (IT) can be used to bring a group of experts in any field of engineering closer together by allowing them to communicate and exchange information and opinions. The central feature of this research study is the integration of these hitherto separate areas of Information Technology (IT). In this thesis an adaptable Graphic User Interface Centred application comprising a Knowledge-Based Expert System (DEMARECEXPERT), a Database Management System (REPCON) and Evaluation program (ECON) alongside visualisation technologies is developed to produce an innovative platform which will facilitate and encourage the development of knowledge in concrete repair. Diagnosis, Evaluation, MAintenance and REpair of Concrete structures (DEMAREC) is a flexible application which can be used in four modes of Education, Diagnostic, Evaluation and Evolution. In the educational mode an inexperienced user can develop a better understanding of the repair of concrete technology by navigating through a database of textual and pictorial data. In the diagnostic mode, pictures and descriptive information taken from the database and performance of the expert system (DEMAREC-EXPERT) are used in a way that makes problem solving and decision making easier. The DEMAREC-EXPERT system is coupled to the REPCON (as an independent database) in order to provide the user with recommendations related to the best course required for maintenance and in the selection of materials and methods for the repair of concrete. In the evaluation mode the conditions observed are described in unambiguous terms that can be used by the user to be able to take engineering and management actions for the repair and maintenance of the structure. In the evolution mode of the application, the nature of distress, repair and maintenance of concrete structures within the extent of the database management system has been assessedT. he new methodology of data/usere valuation could have wider implications in many knowledge rich areas of expertise. The benefit of using REPCON lies in the enhanced levels of confidence which can be attributed to the data and to contribution of that data. Effectively, REPCON is designed to model a true evolution of a field of expertise but allows that expertise to move on in faster and more structured manner. This research has wider implications than within the realm of concrete repair. The methodology described in this thesis is developed to provide tecýnology transfer of information from experts, specialists to other practitioners and vice versa and it provides a common forum for communication and exchange information between them. Indeed, one of the strengths of the system is the way in which it allows the promotion and relegation of knowledge according to the opinion of users of different levels of ability from expert to novice. It creates a flexible environment in which an inexperienced user can develop his knowledge in maintenance and concrete repair structures. It is explained how an expert and a specialist can contribute his experience and knowledge towards improving and evolving the problem solving capability of the application.
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Muhenje, Mariura. "Applying the DER rating system for the visual assessment of defects on concrete dams." Master's thesis, Faculty of Engineering and the Built Environment, 2021. http://hdl.handle.net/11427/33840.
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NamWater is responsible for the management and maintenance of Namibia's main dams, amongst the many other infrastructure assets under their ownership. They have, as a result, devised asset management policies and practices with the aim of reaping the benefits of asset management. Additionally, they have aligned themselves with the current approaches to dam safety management in managing the dams. These current approaches do however not provide for a guided and standard approach when it comes to the visual assessment of surface defects on the dam elements. This may result in varying assessment outcomes from different individuals based on their differences in training and experience. The DER rating system used for the rating of defects on road structures, as input into the STRUMAN BMS used by SANRAL and other entities, provides for a standard approach to visually assessing the defects on these road structures. A study by Gombele (2017:79) has also demonstrated the possibility of using the DER rating system for the assessment of defects on cooling towers in a power generation environment. Additionally, the rating of defects can also play a role in dam risk determination, as demonstrated in the CIRIA 1 Project RP568 risk assessment methodology (Morris, Hewlett and Elliott, 2000:15). In quest for a standard and guided approach for visually assessing surface defects on dam elements, this study applied the DER rating on selected elements of three NamWater dams. The approach was by initially identifying dam elements that are deemed equivalent to the bridge items in the TMH19: Part A. There are variations in the design and functions of the dam elements versus those of bridge elements and thus the relevance of the defects may also vary for the two structure types. Thus, the focus of this study was on using the DER rating system to only assess the surface defects on the dam elements. This may be useful for the initial phase of a condition assessment for dams whereby it can provide a quantifiable indication of durability issues. While the study was able to demonstrate the possibility of using the DER rating system to assess defects such as cracks, spalling and erosion on the surfaces of dam elements, gaps where identified in its applicability. Only 33% of the bridge items in the TMH19: Part A were deemed relevant for the visual assessment of the dam items, coupled with the significant amount of U (unable to inspect) ratings given during the assessment. Furthermore, of the identified defects, a significant amount was given a low Relevancy rating (R) meaning that they are of a low relevance to the structural integrity of the dam structure. This may be due to the fact that the guiding tables used are originally for bridge items and thus not entirely suitable for dams. For the DER rating system to be applied extensively to dam items, defects that are specific to dam elements will therefore need to be incorporated into the guiding tables. Additionally, the weighting of the ratings for certain defects would need to be revised to specifically align with the consequence of the defect on the dam item. This process may require the compilation of a database of historical defects, guided by expert engineering judgement, to provide for guiding tables that are specific to dams. Assessment of more dams that vary in age, type, and performance may also be required to get a more diversified outcome of the applicability of the DER rating system on dams.
7
Lacroix, Francis. "Non-Destructive Condition Assessment of Concrete Slabs with Artificial Defects Using Wireless Impact Echo." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/41575.
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This thesis presents the development and validation of a new wireless Impact Echo (IE) system for condition assessment of reinforced concrete slabs. The new IE prototype was compared with other commercially available non-destructive testing (NDT) devices used for similar purposes, namely Ground-Penetrating Radar (GPR) and Ultrasonic Pulse Echo (UPE). Monitoring and structural inspections are critical to effective management of civil infrastructure and NDTs can enhance the quality of condition assessments by providing objective visualizations of the interior of a structural element.
The IE method, first developed in the 1980s, has seen few advancements in the last 20 years. The method has been standardized and used on site, but the underlying technology has become outdated. The data obtained from the transducer is difficult to interpret and requires a computer to post-process it before being usable, thus limiting the direct feedback of the method when conducting tests on-site. Because of those limitations and the test being relatively more time consuming than other alternatives, the method is lacking in usability. A new prototype IE device was designed and built by the project industry partner, FPrimeC Solutions. The methodology followed the traditional approach, but it was designed to work with today’s technology. The device is operated wirelessly via a Bluetooth connection, uses smaller-sized electronic components, and connects with a user-friendly interface on a small tablet to set-up the tests and compute the results immediately. The first part of the project focused on product development by testing iterations of the prototype and providing user feedback to improve the device and accompanying software.
The second part of the project aimed to validate the new technology using a set of three large reinforced concrete slabs containing artificial defects. The studied points of interest were sound concrete, effect of boundaries and steel reinforcements, vertical cracks, presence of a hollow conduit, artificial voids and delamination. The IE results were also compared with those from commercial GPR and UPE devices. GPR was found to be the quickest method by far, although the results gathered seemed to be limited by the presence of steel reinforcement and also failed to locate certain defects. UPE was a bit slower than GPR, but was generally able to locate more accurately the artificial flaws created in the test specimens. The results showed poor definition of the flaws making it difficult sometimes to properly locate them. The UPE results also seemed to be negatively affected by the presence of reinforcement which were causing frequent abnormal values. Lastly, the IE method was used. This method was greatly improved during the first phase, but it is still a time-consuming method. The value of the data, however, has great potential when compared to the other options. It accurately located most of the flaws generated and was practically unaffected by the presence of steel reinforcing bars. Also, with further analysis of the data, it was possible to determine the depth of some of the flaws accurately.
Due to the time-consuming testing phase and the longer analysis of the data required to obtain the higher quality of results, this study suggests that IE is not likely to be the best choice for a general inspection of a large area (depending on the nature of the information needed). Rather, it is suggested to first conduct a general review of the structure using a quicker method like GPR to locate the problematic areas. After that, refining the grid at key locations to test with IE should provide the best quality of data in a reasonable amount of time.
8
Zhu, Zhenhua. "Column recogniton and defects/damage properties retrieval for rapid infrastructure assessment and rehabilitation using machine vision." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/44768.
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No matter how inspection techniques have been advanced, manual visual inspection is currently still the first and fundamental step in assessing civil infrastructure. If no sign of deterioration has been spotted in manual inspection, any future inspection actions is not necessary to take. However, manual inspection has been identified with several limitations including the qualitative nature of inspection results, the time-consuming inspection process, and the heavy reliance on inspectors' and/or engineers' experience. In order to overcome these limitations, automated visual inspection systems have been proposed to enhance and/or replicate the manual inspection process. A number of image processing methods have been developed in detecting defects (i.e. coating rusts) and damage (i.e. cracks) on civil infrastructure. Their effectiveness has been verified in inspecting structures, such as bridges, underground pipes, and tunnels.
Although existing methods are effective in finding defects and damage from digital images, missing two important links limits their application for rapid infrastructure assessment and rehabilitation. The first link is the correlation between the defects/damage and the structural members that the defects/damage lie on. The second link is the relationship between the defects/damage and their impacts on the structural members.
The purpose of this research is to investigate the way of establishing these two links. It is focused on the retrieval of critical structural members and defects/damage information from images/videos, and then the utilization of this information for automated and rapid assessment and rehabilitation of civil infrastructure. Specifically, a combination of techniques from the areas of visual pattern recognition, digital filtering, and machine vision have been used in order to develop a set of methods for concrete column recognition, crack properties retrieval, and air pockets and discoloration detection and evaluation. The methods proposed in this research were implemented in a Microsoft Visual Studio environment, and tested on the real images/videos of concrete structures inflicted with cracks, air pockets and discoloration. The test results indicated that the methods could automatically recognize concrete columns, correctly measure the properties of the cracks in a crack map, and accurately evaluate the impacts of air pockets and discoloration on the visual quality of concrete surfaces.
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Chen, Jun. "Ultra-accelerated assessment of alkali-reactivity of aggregates by nonlinear acoustic techniques." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34803.
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This research develops two novel experimental techniques based on nonlinear acoustics/ultrasound to provide an ultra-accelerated characterization of alkali-reactivity of aggregates. Alkali-silica reaction (ASR) is a deleterious reaction occurring between reactive siliceous minerals present in some aggregates and alkalis mainly contributed by the cement, but also present in some deicing chemicals. With increasing reports of ASR-induced damage in transportation structures, there is a critical need for fast and reliable test methods for the screening of aggregates and aggregate/paste combinations. Currently, the accelerated mortar bar test (AMBT), which measures expansion, is the most commonly used test method. Also used is the concrete prism test (CPT), another expansion-based method, which requires at least one year testing time, limiting the practical utility of this method. In addition, petrographic analysis can be performed to identify potentially reactive minerals in aggregates but requires training and may not be appropriate for assessment of aggregate/paste combinations. Finally, linear acoustic methods such as wave speed and attenuation measurements can be used for the assessment of ASR, but the sensitivity of linear acoustic methods to ASR-induced damage is considered to be relatively low. Therefore, critical limitations exist in the existing test methods.
In light of recent advances in nonlinear acoustics (which are more sensitive to small-scale damage than linear acoustics), the purpose of this research is the development and assessment of an accelerated method for evaluating the potential for alkali reactivity in aggregate and aggregate/paste combinations by combining advanced ultrasonic methods with standard test procedures. In fact, two nonlinear acoustic methods are developed under this research - nonlinear wave modulation spectroscopy (NWMS) and nonlinear impact resonance acoustic spectroscopy (NIRAS) - and are used to characterize the changes in material nonlinearity as a result of the progressive ASR damage during the standard mortar bar and concrete prism testing. Following the AMBT and CPT, nonlinear acoustic techniques are applied to both mortar bars and concrete prism samples. Nonlinearity parameters are defined as the indicator of growing ASR damage, and measurement results clearly show that these nonlinearity parameters are more sensitive to the ASR damage than the linear parameters used in the linear acoustic measurements, particularly at early ages. Different aggregates with varying alkali-reactivity are effectively distinguished with the proposed experimental techniques in a timely manner, particularly for those aggregates with similar levels of reactivity, as determined by AMBT.
The effect of a Class C fly ash addition on nonlinear properties was also investigated using the NIRAS measurements through a comparison of test results between mortar samples blended with fly ash and without fly ash. As complementary supports of the experimental results, petrographic analyses and theoretical modeling are also performed, and these results are well correlated with results from the NWMS and NIRAS techniques.
Through a comparison with results from accompanying expansion measurements and linear acoustic methods, the proposed nonlinear acoustic techniques show their advantages to accelerate the assessment of alkali-reactivity of aggregates. Under AMBT, reactive aggregates were identifiable as early as a few days of testing. With CPT, reactive aggregates were differentiated as early as a few weeks. Overall, the coupling of the developed nonlinear test methods with standard expansion tests suggests that test durations could be potentially reduced by half, especially for AMBT tests.
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Chies, Josué Argenta. "Ensaios não destrutivos em concreto : detecção de falhas no interior de estruturas de concreto com o uso de ultrassom." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/127927.
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A aplicação de Ensaios Não Destrutivos (END) é considerada uma alternativa para monitorar o estado das estruturas de concreto armado, principalmente quando ocorrem falhas de projeto, erros de dosagem, problemas na mistura, transporte ou lançamento do concreto. A medida da Velocidade de Pulso Ultrassônico (VPU) é um END que vem sendo usado comumente em diversas áreas da engenharia civil, devido à facilidade da operação, ao seu baixo custo, à rapidez na execução dos testes e à ausência de danos ao material analisado. O objetivo deste trabalho consiste em apresentar o resultado de uma pesquisa experimental, que visou estudar a influência que determinadas variáveis operacionais exercem sobre os resultados obtidos nos ensaios de VPU e qual a real capacidade de penetração e detecção de defeitos de diversas magnitudes. As medições foram realizadas utilizando o ultrassom pelo modo de transmissão indireta, pois esta é a alternativa que mais se adapta às condições verificadas no exame de estruturas reais de concreto armado. Primeiramente, foram moldados em laboratório dois blocos de concreto, com dimensões próximas às encontradas em estruturas reais de grande porte: um com armadura nas duas faces e outro sem armadura. Em ambos os elementos foram introduzidos objetos para simular possíveis falhas de concretagem. Em uma segunda etapa, foram realizadas perfurações visando identificar a capacidade de detecção de vazios da técnica de VPU para diferentes profundidades. Os resultados são apresentados na forma de imagens geradas através de software e por meio de analises estatísticas. Este estudo verificou que a escolha dos parâmetros de ensaio é um fator determinante para permitir a interpretação correta dos resultados, salientando-se que a experiência do operador e as dimensões de grid são os parâmetros que mais interferem na interpretação dos dados.The use of Non-destructive Testing (NDT) methods is considered an alternative to monitor the behaviour of reinforced concrete structures, especially when there are design problems or errors related to concrete mixing, transport, placement and casting errors. The Ultrasonic Pulse Velocity (UPV) method is a Non-Destructive Test that is gaining acceptance. The test has been commonly used in various civil engineering areas due to the fact that it is easy to operate and rapid to perform, and to the low cost and lack of damage to the tested material. The objective of this work is to present the results of an experimental research that aimed to study the influence of certain technological variables on the measurements obtained from UPV tests. The work also aims to gather data to assess the penetration capacity of the US waves and their ability to detect defects of various dimensions. The measurements were performed using the indirect transmission mode, to simulate real work conditions on large structures. Firstly, two massive concrete blocks were cast in the laboratory, with dimensions close to real life structures: one with steel reinforcement on both sides and the other without reinforcement. Objects were introduced in both elements to simulate possible defects due to casting. In a second stage, perforations were conducted in the concrete elements to identify the void detection capability of the UPV technique for different depths. The results are presented by images generated by specific software and by using statistical analysis. This study found that the test parameters influence significantly the correct interpretation of the results. The operator experience and the grid dimensions are the parameters that most influence UPV data analysis.
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Juočys, Rokas. "Virbališkių hidromazgo būklės ir gelžbetoninių konstrukcijų patikimumo tyrimai." Master's thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20120530_123817-66119.
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Nors gelžbetonis yra patvari statybinė medžiaga, tačiau iš šios medžiagos pastatytose konstrukcijose labai dažnai pirma laiko atsiranda įvairių pažaidų ir jos pradeda irti.
Tyrimų objektas – Virbališkių hidromazge esantys hidrotechnikos statiniai. Virbališkių hidromazgas yra netoli Kačerginės Nemuno žiedo, šalia Dievogalos upelio vagos. Šio darbo metu buvo nustatyta ir įvertinta hidrotechnikos statinių būklė vizualiai. Naudojant neardančius metodus, nustatytas gelžbetoninių konstrukcijų betono stipris gniuždant c (MPa), įvertint hidromazge esančiu atraminių sienų projektinį bei esamą patikimumą, nustatyti kaip galėjo kisti konstrukcijos patikimumas sumažinus arba padidinus armatūros skerspjūvio plotą, bei padidinus arba sumažinus atstumus tarp strypų.
Atlikus vizualinius Virbališkių hidromazgo tyrimus pastebėta, kad visos hidromazge esančios konstrukcijos turi pažaidų, bei konstrukcijų neatitikimo su projektu t.y. atraminėse sienose įrengta dvigubai mažiau deformacinių siūlių negu, kad jų buvo suprojektuota (6 suprojektuotos, įrengtos 3 deformacinės siūlės), žemutiniame bjefe įrengtas šlaitų tvirtinimas buvo numatytas iš surenkamų gelžbetoninių plokščių, o įrengta iš monolitinio betono..
Atlikus betono stiprio nustatymo tyrimus neardančiaisiais metodais su Šmidto plaktuku gauta, kad konstrukcijos atitinka statybos metu galiojusias normas, taip pat projekte numatytas betono klases hidromazgo konstrukcijoms.
Atlikus patikimumo skaičiavimus gauta, kad konstrukcija šiai... [toliau žr. visą tekstą]Although reinforced concrete is a durable building material, but very often early defects occur in such structures and they begin to decay. The object of research – hydraulic structures in Virbališkis hydroscheme. Virbališkis hydroscheme is situated near Kačerginė Nemunas ring, near the Dievogala stream bed. The visual condition of hydraulic structures has been identified and evaluated in this work. The concrete compressive strength of reinforced concrete structures c (MPa) was defined using non – destructive methods, the actual and design reliability of retaining walls located in the hydroscheme were estimated, the reliability of the structure after the increase or decrease of the cross-sectional area of reinforcement as well as after the decrease or increase of the distance between the rods was defined. After the visual surveys of Virbališkis hydroscheme it was found that all the constructions situated in the hydrosheme have defects and non-compliance with the construction project, i.e., only half of the expansion joints were arranged in the retaining walls (6 designed and only 3 expansion joints were arranged). Reinforcemen of the slopes arranged in the downstream dam had to be from prefabricated reinforced concrete panels however, it was equipped with a monolithic concrete. After the fulfiment of concrete strength tests using non-destructive... [to full text]
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Bučilová, Iveta. "Aspekty navrhování staveb zaměřené na životnost." Master's thesis, Vysoké učení technické v Brně. Ústav soudního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-241153.
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The master´s thesis discusses the life of building structures in terms of selected causes of failures are listed and discussed in ISO 16204 - "Durability - Service life design of concrete structures". The selected causes of failures will be carbonation and frost resistance of concrete. These causes will be performed computational analyzes for few types of concrete, based on these anayzes will be possible to compare and analyze the requirements specified in standards ČSN EN 1990, ČSN EN 1992 and ČSN EN 206.
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Zhang, Wulong. "Influence des défauts de mise en place du béton et des fissures fonctionnelles transversales sur la corrosion des armatures des structures en béton exposées aux chlorures." Thesis, Toulouse, INSA, 2020. http://www.theses.fr/2020ISAT0009.
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Le but de la thèse est d'étudier le comportement à la corrosion des armatures en acier dans le béton exposé aux chlorures, en relation avec l'impact des défauts induits par la mise en place du béton pour les armatures situées en haut de coffrage, et en relation avec la fissuration transversale artificielle ou induite par le chargement mécanique.Trois parties principales sont incluses dans cette thèse. La première partie étudie les caractéristiques de l'interface acier-béton, y compris la distribution des bulles d'air à l'interface acier-béton, les propriétés des défauts d’interface dus au ressuage du béton frais et la microstructure des produits d'hydratation du ciment à l'interface acier-béton, et l’influence des défauts de mise en place des barres supérieures sur la pénétration des ions chlorure à l'interface acier-béton. La deuxième partie étudie l'effet des défauts de mise en place sous les barres supérieures et des fissures artificielles sur le comportement à la corrosion des armatures en acier au début de la période de corrosion en présence de chlorures, incluant la distribution de la corrosion par piqûres et l'analyse cinétique du processus de corrosion. La troisième partie discute de l'influence des défauts de mise en place sous les barres supérieures sur le comportement à la corrosion des armatures de poutres naturellement corrodées sous une charge maintenue pendant une durée d'exposition relativement longue, y compris les cartes de fissuration induite par la corrosion, les profils de chlorures, les pertes de section d'acier et la répartition de la corrosion le long des armatures en acier.Selon les résultats expérimentaux de la première partie, il a été constaté que des bulles d'air sont principalement apparues à l'emplacement de la zone de nervure du côté inférieur de l'acier haute adhérence selon la direction de coulage. Des vides de ressuage sont toujours apparus dans la zone inférieure de l'interface acier-béton, tandis que la zone supérieure de l’interface acier-béton était plus dense que celle de l'interface inférieure. Les cristaux de Portlandite et d’Ettringite sont principalement formés et développés à l'interface inférieure acier-béton. La présence de vides de ressuage a facilité le transport des ions chlorure à l'interface acier-béton.Dans le cas de la deuxième partie, la corrosion s'est amorcée du côté inférieur des barres d'armature en acier selon la direction de coulage. Les barres d'acier dans le béton avec fissure artificielle présentaient un taux de corrosion plus élevé que les barres d'acier dans le béton sans fissure artificielle au début de la période.Pour la troisième partie, les défauts de mise en place pour les barres supérieures sont le facteur d'impact le plus significatif accélérant la détérioration du béton armé. Dans le cas des barres de compression, présentant des défauts de coulage, bien que la distribution de la corrosion soit aléatoire, la corrosion était susceptible de se produire du côté inférieur des barres de compression faisant face aux défaut de ressuage. Après le développement des fissures induites par la corrosion, la corrosion s'est progressivement développée tout autour du périmètre des barres d'armature, de sorte que le défaut de coulage n'a plus affecté le processus de corrosion. Dans le cas des barres en traction, avec des défauts de coulage, la corrosion commence aux fissures de service et se développe ensuite préférentiellement à la surface inférieure de la barre. Sans défauts, la corrosion commence aux fissures de service mais ne se développe pas le long des barres de traction. Ce n'est que lorsque la teneur en chlorures à la profondeur de l'armature atteint une valeur critique que la corrosion se développe le long de la barre tendue, de préférence à la surface extérieure de la barre en raison de sa teneur en chlorures probablement plus élevéeThe purpose of the thesis is to investigate the corrosion behavior of reinforcing steel in concrete under chloride environment, in relation to the impact of top-casting-induced defects in the steel-concrete interface, artificial transverse crack and load-induced transverse cracks.Three main parts are included in this thesis. The first part investigates the characteristics of steel-concrete interface, including the distribution of air bubbles at steel-concrete interface, the properties of bleed water voids and the microstructure of cement hydration products at steel-concrete interface, and the effect of top-casting defects on the chloride ions penetration at steel-concrete interface. The second part studies the effect of top-casting defects and artificial crack on the corrosion behavior of steel rebars in early corrosion period under chloride environment, containing the pitting corrosion distribution and the kinetic process analysis of steel rebar in concrete. The third part discusses the influence of top-casting-induced defects on the corrosion behavior of reinforcing steel of naturally corroded beams under sustained loading in a relative long exposure term, including the cracking maps of RC beams, the chloride profiles, the cross-sectional loss of reinforcing steel and the distribution of corrosion on steel rebars.According to the experimental results from the first part, it was found that, air bubbles mainly appeared at the location of the rib zone of the bottom side of deformed steel according to the casting direction. Bleed water voids always appeared at the bottom interface of steel-concrete, while the top interface of steel-concrete was denser compared to that of the bottom interface. Portlandite crystals and ettringites mainly nucleated and grown at the bottom interface of steel-concrete. The presence of bleed water voids facilitated the transportation of chloride ions at the steel-concrete interface.In the case of the second part, corrosion mainly initiated at the location of rib zone of the bottom side of steel rebar according to the casting direction due to the presence of top-casting defects. The steel bars in concrete with artificial crack exhibited a higher corrosion rate corrosion compared to the steel bars in concrete without artificial crack in early period. However, after this period, a similar corrosion rate was identified for steel rebars in concrete with or without artificial crack.For the third part, top-casting defects are the most significantly impacting factor accelerating the deterioration of reinforced concrete. In the case of compressive bars, with top-casting defects, although the distribution of corrosion was random, corrosion was manly prone to occur at the bottom side of compressive bars facing top-casting defects. Without top-casting defects, the corrosion was more prominent on the outside part of rebars facing the concrete surface exposed to chloride ingress. After the presence of corrosion-induced cracks, corrosion gradually developed all around the perimeter of rebars, with the result that top-casting defect no longer affected the corrosion process. In the case of tensile bars, with top-casting-induced defects, corrosion starts at service cracks and then develops preferentially at the bottom surface of the tensile bar. Without top-casting defects, corrosion starts at service cracks but does not develop along the tensile bars. It is only when the chloride content at the depth of reinforcement reaches a critical value that corrosion develops along the tensile bar-preferentially at the outside surface of the rebar because of its probable higher chloride content
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In, Chi-Won. "Defect characterization in heterogeneous civil materials using ultrasound." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47545.
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Asphalt and Portland cement concrete constitutes a significant portion of the total infrastructure all over the world. It has been reported that much of this concrete infrastructure is now approaching or has already passed its original design life. Thus it is critical to be able to quantitatively assess the condition of these concrete components. In order to rehabilitate or repair the civil infrastructure, nondestructive evaluation (NDE) techniques have been of great interest for infrastructure management agencies. However concrete components present several specific NDE challenges that must be addressed. . Concrete naturally exhibits large scale heterogeneous microstructure with a great deal of local material property variability, For this reasons, many conventional NDE techniques that work well for steel and other homogeneous materials cannot be applied to concrete; concrete is unable to transmit high frequencies, as the heterogeneity of the concrete causes signals of smaller wavelengths or wavelengths equal to the nominal aggregate size to be scattered and severely attenuated. Nevertheless, progress has been made towards accurate and reliable in-place NDE of concrete structures and materials, for example impact echo, ultrasonic pulse velocity method, and the ultrasonic wave transmission method. However, the detection of smaller sized defects or remote defects that are located away from the testing location still pose problems. In addition, the large size and potential limited access conditions of civil structures raise additional challenges. To overcome the limitations of current NDE techniques for concrete, this research considers two different types of ultrasonic waves (coherent and incoherent wave) to quantitatively characterize and monitor defects in heterogeneous concrete materials. The global objective of this research is to determine the feasibility and applicability of using these ultrasonic waves as a global, rapid, reliable, and non-biased technique for the routine screening of defects or monitoring of concrete structures and materials. Three different problems are considered: 1) characterization of segregation in asphaltic concrete, 2) crack depth determination in pier cap of concrete bridge structure, and 3) monitoring of self-healing process in cement-based concrete.
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Chan, Hon-Fung Cyril. "Non-destructive testing of concrete piles using the sonic echo and transient shock methods." Thesis, University of Edinburgh, 1987. http://hdl.handle.net/1842/13349.
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Šadzevičius, Raimondas. "Aplinkos poveikio žemių užtvankų šlaitų tvirtinimo gelžbetoninėms plokštėms modeliavimas ir analizė." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2005. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2005~D_20051108_145159-47758.
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In the dissertation evaluated frost influence to the change of physical–mechanical properties of the reinforced concrete slabs for earth dam slope protection. Established ice thermal expansion linear load acting the slabs and proposed more exact calculation of this load. Evaluated deterioration indices and defects influence to slabs state and durability.
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McParland, Christopher. "The analysis of defect evolution in a set of reinforced concrete bridges." Thesis, University of Ulster, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270462.
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Rodrigues, Flavio Aparecido. "Preparo e caracterização de materiais a base de cimento isentos de macro-defeitos." [s.n.], 1995. http://repositorio.unicamp.br/jspui/handle/REPOSIP/250462.
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Orientador: Ines JoekesTese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica
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Doutorado
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Huethwohl, Philipp Karl. "Bridge damage detection and BIM mapping." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/285562.
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Bridges are a vitally important part of modern infrastructure. Their condition needs to be monitored on a continuous basis in order to ensure their safety and functionality. Teams of engineers visually inspect more than half a million bridges per year in the US and the EU. There is clear evidence to suggest that they are not able to meet all bridge inspection guideline requirements. In addition, the format and storage of inspection reports varies considerably across authorities because of the lack of standardisation. The availability of a comprehensive and open digital representation of the data involved in and required for bridge inspection is an indispensable necessity for exploiting the full potential of modern digital technologies like big data exploration, artificial intelligence and database technologies. A thorough understanding of bridge inspection information requirements for reinforced concrete bridges is needed as basis for overcoming the stated problem. This work starts with a bridge inspection guideline analysis, from which an information model and a candidate binding to Industry Foundation Classes (IFC) is developed. The resulting bridge model can fully store inspection information in a standardised way which makes it easily shareable and comparable between users and standards. Then, two inspection stages for locating and classifying visual concrete defects are devised, implemented and benchmarked to support the bridge inspection process: In a first stage, healthy concrete surfaces are located and disregarded for further inspection. In a second hierarchical classification stage, each of the remaining potentially unhealthy surface areas is classified into a specific defect type in accordance with bridge inspection guidelines. The first stage achieves a search space reduction for a subsequent defect type classification of over 90% with a risk of missing a defect patch of less than 10%. The second stage identifies the correct defect type to a potentially unhealthy surface area with a probability of 85%. A prototypical implementation serves as a proof of concept. This work closes the gap between requirements arising from established inspection guidelines, the demand for holistic data models which has recently become known as "digital twin", and methods for automatically identifying and measuring specific defect classes on small scale images. It is of great significance for bridge inspectors, bridge owners and authorities as they now have more suitable data models at hand to store, view and manage maintenance information on bridges including defect location and defect types which are being retrieved automatically. With these developments, a foundation is available for a complete revision of bridge inspection processes on a modern, digital basis.
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Hughes, Peter. "An investigation into marine biofouling and its influence on the durability of concrete sea defences." Thesis, University of Central Lancashire, 2014. http://clok.uclan.ac.uk/10636/.
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This research has investigated marine biofouling and its influence on the durability of concrete sea defences using on-site and laboratory-based studies. The study was divided into three main phases namely: the surface analysis of armour concrete, the study of algal colonisation within the matrix and investigations into the presence of a bacterial biofilm within freshly hardened armour concrete. The effectiveness of photocatalytic coatings as a non-toxic anti-fouling strategy and cell attachment to synthetic fibres was also studied. It was found that algal growth quickly developed at the interface of inclusions within the matrix and that power washing with the use of Dairy Hypochlorite to remove this accelerated wear, leading to significant mass loss. It was also observed that bacterial growth within local beach sand, which was used in the production of the revetment armour units, survived the concrete manufacturing process. Bacteria were cultured from the sand and were found to match the Actinomycete like growth in the freshly hardened matrix of armour concrete. This thesis proposes a holistic model for biofouling of fibre reinforced marine concrete in which algal growth around inclusions facilitates a complex process of biodeterioration. Bacterial filamentous growth around and through synthetic fibres embedded in the new concrete mix, appears to be detrimental to the long term durability of synthetic fibres. Subsequent algal colonisation on the surface of newly placed units appeared to quickly penetrate the surface through exposed fibres and percolated interfaces of inclusions, subsequently weakening their bond. During the manufacture of the armour units, aggregate segregation in the 90° corners in the bottom of the form created a weaker matrix in the surface region most exposed to biodeterioration, the full force of wave action and power washing. The main conclusions from this study are: • Synthetic fibres used at the study site are inappropriate for marine concrete, particularly in algal rich waters, within the inter-tidal zone where beach sand is used in the concrete mix. Amendments to Concrete Society Technical Report No. 65: Guidance on the use of Macro-synthetic-fibre-reinforced concrete have been recommended. • Bacterial loaded beach sand is detrimental to the durability of marine concrete in the inter-tidal zone and amendments are recommended to PD 6682-1:2013 Aggregates for concrete (BSI, 2013a) in order to highlight this concern. This UK guidance suggests limiting values for aggregate properties within the ranges permitted in BS EN 12620 (BSI, 2013) but does not place any limits on microorganisms present in beach sand. Further work is needed into the susceptibility of synthetic fibres to crystal growth. Alterations in the manufacture of armour units have been recommended by this author.
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Scabello, Daniel Torres. "Estudo sobre a aplicabilidade do processo de inventário funcional de pavimentos rígidos com o emprego do equipamento Pavement Scanner e validação de resultados." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/3/3138/tde-16072018-084749/.
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O gerenciamento de uma malha rodoviária engloba avaliações constantes das condições estruturais e, principalmente, funcionais. Assim sendo, uma forma de coleta automatizada, realizada em velocidades de tráfego, em que a influência humana possa ser desconsiderada, está em desenvolvimento na engenharia rodoviária brasileira, assim como é visto internacionalmente. O presente trabalho tem como objetivo a contribuição para o processo de avaliação funcional de pavimentos através do estudo sobre a aplicabilidade do processo de inventário funcional de pavimentos rígidos com o emprego do equipamento Pavement Scanner. Para tanto, após a revisão bibliográfica sobre a sistemática de inventário de pavimentos rígidos e também sobre o equipamento Pavement Scanner, seções testes foram definidas e avaliadas de acordo com o método tradicional de levantamento da superfície do pavimento (ICP - DNIT 062/PRO, DNIT 060/PRO), o método volumétrico tradicional de mancha de areia para avaliação de macrotextura (ASTM E 965/96), através de imageamento com análise de imagens obtidas no trecho e sob a utilização do equipamento Pavement Scanner. Com os resultados foi realizada uma análise estatística destas técnicas utilizadas, demonstrando a viabilidade de utilização do equipamento e do procedimento de análise adotado.The management of a road network encompasses constant assessments of structural conditions and, above all, functional conditions. Thus, a form of automated survey, carried out at traffic speeds, in which human influence can be unconsidered, is under development in Brazilian road engineering, as it is seen internationally. This present work aims to contribute to the process of functional assessment of pavements through the study of applicability of the functional inventory process of rigid pavements with the use of Pavement Scanner equipment. In order to do so, after the literature review of rigid pavement inventory and Pavement Scanner equipment, test sections were defined and evaluated according to the traditional method of surface survey (ICP - DNIT 062 / PRO, DNIT 060 / PRO), the traditional sand patch volumetric method for the evaluation of macrotexture (ASTM E 965/96), through imaging analysis from the test sections and under the use of Pavement Scanner equipment. With the results, a statistical analysis of these techniques were performed, demonstrating the feasibility of using the equipment and the analysis procedure adopted.
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Wünsche, Dominik. "Diagnostika a hodnocení mostní konstrukce." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2021. http://www.nusl.cz/ntk/nusl-433535.
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The diploma thesis deals with the issue of bridge strustures, especially their diagnostics and evaluation. The work consists of two parts, theoretical and practical. The theoretical part deals with the basic description and division of bridge structures, brigde inspections and test methods, especially those that were used in the thesis during bridge inspections. The practical part includes a visual inspection of two bridges, their description, detection of faults and defects and their documentation. In the practical part, the basic maretial characteristics of concrete bridges were determined, the condition of structures was assessed and a proposal for the elimination of failures and defects was developed. In the end, the work deals with the evaluation of both bridges.
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Kirschbaum, Adam. "Hodnocení konstrukcí průmyslových objektů podle ČSN ISO 13822." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2016. http://www.nusl.cz/ntk/nusl-240048.
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This diploma thesis deals with the evaluation of the constructions of the industrial buildings according to the ČSN ISO 13822 Standard. In the first, theoretical part, the procedures of research and evaluation of existing reinforced concrete constructions based on the ČSN ISO 13822 and ČSN 73 0038 Standards are described. Further, the theoretical part is focused on the diagnostic methods used during the evaluation of these constructions. The practical part focuses on the evaluation of the three industrial reinforced concrete buildings. It includes information about the building, the description of defects, diagnostics and the appraisal of measuring. The last part deals with a static calculation of selected parts of the supporting construction.
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Rozbroj, Lukáš. "Diagnostika železobetonového mostu." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2015. http://www.nusl.cz/ntk/nusl-227490.
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This thesis contains diagnostics of a reinforced concrete girder bridge in the municipality of Újezd u Brna. The aim is to conduct an inspection of the bridge, gather quality photo-documentation of defects and failures and design and conduct a diagnostic examination of such extent that would be necessary for judging the load bearing capacity of the bridge. The result of this thesis is the determined load bearing capacity and a proposal of measures required to keep the bridge functional.
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Louhi, Amine. "Intégrité des tours aéroréfrigérantes en béton armé sous sollicitations extrêmes : Vent et séisme." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0114/document.
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Il est prévu d’augmenter la durée de vie des centrales nucléaires actuellement opérationnelles. Le vieillissement des structures en béton armé telles que les tours aéroréfrigérantes doit être évalué, son incidence sur la capacité portante calculée. Dans le cas de fortes dégradations, le renforcement doit être envisagé, afin d’assurer la pérennité de ces tours face aux sollicitations extrêmes telles que les tempêtes de vent et les séismes. Ce travail vise à quantifier les effets néfastes que peut générer la réduction de section des aciers induite par la corrosion, en particulier sur la capacité portante des tours dans des conditions de sollicitations extrêmes monotones ou cycliques de types vent et séisme. Ces sollicitations sont certainement les plus sévères, entrainant la structure dans le domaine non linéaire, elles sont susceptibles d’induire des endommagements de type fissuration qui dans le cas de sollicitation cycliques peuvent s’avérer néfastes. Des modélisations numériques sont proposées pour déterminer la réponse quasi-statique ou dynamique de la structure, en tenant compte des apparitions de fissures dans le béton et de leur évolution via des lois de comportement appropriées du matériau béton, ainsi que la plastification des aciers. Dans le cas d’une sollicitation sismique, dans le but de comparer les approches de modélisation du séisme et d’évaluer la robustesse des résultats, les réponses dynamiques sont évaluées par trois méthodes différentes de calcul : l’approche dynamique temporelle non linéaire, la méthode spectrale et la méthode modale temporelle. Des études paramétriques portant sur l’amortissement, les combinaisons de charges et les configurations structurales, sont aussi menées. Dans le cas d’une sollicitation de type vent, la technique de renforcement à l’aide de matériaux composite, tel que le tissu de fibres de carbone (TFC) est modélisée. Le comportement de la structure endommagée présentant un taux de corrosion avancée, est évalué dans le régime pré- et post-fissuration, comparativement à la structure intègre. La perte de capacité portante est quantifiée, un renforcement permettant de restaurer l'intégrité et donc d’augmenter la durée de vie de la structure est proposéThe authorities have planned to increase the lifetime of currently operating nuclear power plants. The ageing of reinforced concrete structures such as cooling towers should be evaluated and its impact on the bearing capacity calculated. In the case of significant damage, the strengthening must be considered to ensure the sustainability of these towers facing the risk of storms and earthquakes becoming more and more frequent. This work aims to quantify the adverse effects that can generate concrete cracks and rebar section loss induced by corrosion, especially on the bearing capacity of nuclear power plant cooling towers under monotonic or cyclic extreme load conditions (wind and earthquake). These loads are certainly the most severe, since they take the structure into the nonlinear domain and can induce or amplify cracking damage. Numerical simulations are proposed to determine the quasi-static or dynamic response of the structure, taking into account appearance of concrete cracks and their evolution via an appropriate material concrete law and rebar's yielding. In the case of a seismic load, the responses are evaluated by three different methods; the nonlinear response history analysis (NLRHA), the response spectrum analysis and the modal response history analysis (MRHA) in order to compare the earthquake modeling approaches and to evaluate the robustness of the results. Parametric studies on damping, load combinations and structural configurations, are also performed. In the case of a wind load, the strengthening technique using composite materials, such as carbon fiber reinforced plastic (CFRP) is modeled. The behavior of the damaged structure with an advanced corrosion rate is estimated in the pre- and post-cracking regime, compared to the undamaged structure. The drop of bearing capacity is quantified, a reinforcement designed is proposed to restore the integrity and thus increase the lifetime of the structure
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Gill, Laurence Mark. "Micro-cracking and crack growth in notched concrete and mortar beams." Thesis, 2015. http://hdl.handle.net/10539/16873.
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A dissertation submitted to the Faculty of Engineering, University of the
Wttwatersrand, Johannesburg, in fulfilment of th e degree of Master of
science in Engineering
Johannesburg 1988This dissertation addresses the question of the fracture behaviour of notched concrete and mortar beams. The major purpose of the work was to study the development of the micro-cracked zone and identify the point at which main crack growth began, and thus to characterise concrete and mortar at the start of main crack growth. Notched concrete and mortur beams of width 100 mm, depth either 200 mm or 300 nun, and with a span/depth ratio of three, were tested. Measurements of midspan deflection, midspan load, surface displacements across the fracturing section and ultrasonic pulse transit time were made. Ordinary Portland cement and mineral aggregates were used for the concrete and mortar beams. The J'■integral, surface displacements across the fracturing section and ultrasonic pulse transit time measurements were used to detect the onset of main crack growth. It was found that a reduction in the load carrying capacity of concrete and mortar is possible due to micro-cracking only. The value of the J-integral at the start of main crack growth was found to be essentially the same for concrete and mortar. The value of the J-integral at the start of micro-cracking was ■ < found to be essentially the same for concrete and mortar, and about 40% of the value of the J-integral at the start of main crack growth. The value of the J-integral at the start of micro-cracking and at the start of main crack growth was found, on average, to increase for an increase in beam depth. Surface displacements across the fracturing section showed the tension zone at the start of main crack growth to be approximately twice the size of the compression zone for both concrete and mortar. The'size of the micro-cracked zone, as determined from surface displacements across the fracturing section, was found to be 42% of the residual ligament depth for concrete, and 41% of the residual ligament depth for mortar. Scatter in the results was found to be considerable, thus meaning that only general trends could be identified
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Kuo, Chia-Ying, and 郭嘉穎. "Investigating the Examination Methods for Concrete Lined Dike Defects." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/85656649984561906877.
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碩士國立成功大學
土木工程學系碩博士班
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Cliffy landforms and short rivers having rapid flow velocity are the geographic features in Taiwan.In addition, typhoons, heavy rainfalls and earthquakes are three vital factors to cause severe damage and erosions on the hydraulic structures, such as dikes. Good maintenance of the dikes will decrease the loss of human life and property. Hence, developing quick and reliable methods to assess the dike performance is an essential task In this thesis, naked eye observation, hammer knocking, ground penetration radar and thermography are four major methods to detect defects in the lined dike. Results form different detecting equipments are discussed with the ones using hammer knocking. In addition, the results are also compared with the conventional observation method with naked eyes, as well as, a quantitative LPDRI safety evaluating model. The easy but useful detection method will be suggested for evaluating the performance of different hydraulic structures through discussing the merits and disadvantages of existing methods. At the same time, the suggested method is supposed to result in adequate maintenance under limited budget. Two sections, A and B, of dikes with 85 meters long are located near the converge of Yen-Shui River drainage and An-Shun one. They were selected to be case studies and the current status of dikes were evalutated using the ground penetration radar, thermography and hammer knocking,as well as, naked eye observation. Results of ground penetration radar, thermography and hammer knocking implied the exist of eroded cavity behind the concrete lining at section A, but the dike remained intact at section B. Detecting results using different detecting equipments correlate well with one another. The naked eye observations also showed that repair was required at section A, But no damage revealed at section B. Although section A showed intact appearance after repair when the naked eye observation was conducted, the results using detecting equipments still showed the exist of cavity inside. Thus, using detecting equipments to detect the status of dyke can help the naked eye observation to obtain better assessment in the future. Keyword: ground penetration radar, thermography, dike examination method
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White, Joshua. "Ultrasonic Tomography for Detecting and Locating Defects in Concrete Structures." Thesis, 2012. http://hdl.handle.net/1969.1/ETD-TAMU-2012-05-11097.
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This thesis evaluates a particular ultrasonic nondestructive testing (NDT) system in order to determine its capabilities and limitations in locating defects in concrete structures; specifically tunnel linings, bridge decks, and pavements. The device, a phased-array ultrasonic tomography (UST) system that utilizes shear waves, is a significant advancement in NDT systems. Consequently, there is a need in structural engineering to verify new technologies by assessing their flaw-detecting capabilities in a variety of structural applications.
The UST technique does not currently have a testing methodology that is field-ready. In order to develop a methodology, the system was evaluated based on its ability to detect simulated defects, then taken to the field to evaluate natural structural defects on public tunnels, pavements, and airport runways. Types of concrete defects the system is used to detect and localize include air- and water-filled voids, vertical cracks, horizontal delaminations, and abnormalities such as clay lumps. The device is also used to determine reinforcement depth and spacing as well as concrete thickness measurements.
This research concludes that the UST system is exceptional at locating horizontal delaminations ranging from 0.05-2.0 mm (0.002-0.079 in.), and is able to differentiate between fully debonded and partially-bonded areas. Vertical cracks could only be detected once they begin to form parallel to the testing surface; however, omission of surface details was found to be a strong indicator of crack presence. Backwall surfaces up to a depth of 762 mm (30 in.) were successfully and accurately determined. Air- and water-filled voids as well as reinforcement details such as layout and depth were also successfully determined and located. With the exception of some medium-sized clay lumps (with a diameter of approximately 102 mm, or 4 in.) surrounding reinforcement, all clay lumps tested were also highly successful.
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Maksymowicz, M. "Evaluation of load capacity of concrete railway slab spans with defects." Doctoral thesis, 2008. http://hdl.handle.net/1822/8861.
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Tese de Doutoramento - Área do Conhecimento em EstruturasThis study presents a complete methodology for the load capacity assessment of existing damaged railway slab spans made of reinforced concrete. The databases of the Polish (PKP) and Portuguese (REFER) railway infrastructure administrations are analysed. Furthermore, a study on the reports of international scientific projects i.e. “Sustainable Bridges” and “SAMCO” have lead to a conclusion that from among existing railway bridge stock, simply supported spans are the most common form of construction. Moreover, the spans carrying single tracks dominate in this group. The statistical information based on these sources has been presented in this study. Based on the Author’s observations, consultations with bridge inspectors as well as the literature study, a uniform and multi-level classification system of bridge defects has been presented. This system reflects all the defects that may occur during a bridges service life. Their influence on the load capacity is emphasized. To evaluate the load capacity of damaged structure information on defect parameters is essential. For this reason the Author presented a survey of testing methods to be applied in bridge condition appraisal. To explain the nature of defects in terms of their causes, the taxonomy of degradation mechanisms, leading to these defects, is presented as well. The defects considered in this study have also been presented in terms of their modelling using of various geometry models. The conception of a numerical defect modelling by means of three parameters (i.e. intensity, location and extent) is included. Conclusions following from the statistical survey on the railway bridge stock have induced the Author to analyse the possibility of application of a simplified geometry model of a span – simply supported beam. In order to compare results of the load capacity assessment several numerical analyses have been performed. The range of application of the simplified span model has been established by means of a 5% threshold of difference between results obtained by the considered models. To perform effective analyses of the load capacity of an existing span, the Author created and presented his own program called “Damage Assessment Graphic Analyser” (DAGA). By means of a built-in graphic editor this program allows visualizations in a three dimensional space of a span with defects in the concrete and reinforcing steel, i.e. losses of material and material parameters modifications. This tool automatically performs the static-strength analysis and results, presented as envelopes of cross-section load capacity (for designed as well as current condition – with defects) and bending moments for various load classes. Using the DAGA program a set of parametric analyses (static-strength) has been carried out. Their results have been collected in a knowledge base to be implemented in an expert tool, called ANAlisys of CONcrete DAmages (ANACONDA) based on the hybrid network technology with analytical and neural components incorporated, designed by the Author. At the end of this Thesis the conclusions and directions of further investigation can be found.
A presente tese apresenta uma metodologia avançada para a análise / avaliação da capacidade resistente de pontes ferroviárias com tabuleiro em laje de betão. A análise das bases de dados das administrações ferroviárias polaca (PKP) e portuguesa (REFER), para além do estudo de relatórios recentes de projectos científicos internacionais, tais como exemplo os projectos " Sustainable Bridges" e "SAMCO", permitiram concluir que das pontes ferroviárias existentes a maioria corresponde a soluções simplesmente apoiadas. Entre estas as pontes com via única são claramente o tipo dominante. Neste estudo é apresentada toda a informação estatística dos dados coligidos nessas fontes. Tendo por base as observações do autor, as consultas aos inspectores de pontes, assim como o estudo exaustivo da literatura existente, foi apresentado um sistema de classificação uniforme e multi-nível das anomalias mais comuns em pontes. Este sistema reproduz as anomalias que ocorrem durante o período de vida útil de uma ponte. A influência destas anomalias na capacidade resistente é devidamente abordada. A resposta a este problema tem sido objecto de grande atenção pela comunidade técnica e científica, devido aos desenvolvimentos ocorridos nos métodos experimentais de apoio às inspecções e ao aprofundamento do conhecimento da classificação dos mecanismos de degradação. As anomalias acima mencionadas foram apresentadas, em termos da sua modelação, através de vários modelos geométricos. Para o efeito a modelação numérica de qualquer anomalia é efectuada tendo por base três parâmetros – intensidade, localização e extensão. As conclusões retiradas da análise estatística das pontes ferroviárias existentes induziram o autor a desenvolver um sistema de análise da possibilidade de aplicação de um modelo geométrico, simplificado, para a modelação do efeito das anomalias neste tipo de pontes. O campo de aplicação do modelo simplificado foi estabelecido como válido para as situações correspondentes a 5% de diferença entre os resultados obtidos pelos modelos em questão. Para efectuar as análises da capacidade resistente das pontes em questão, o autor desenvolveu um programa de cálculo automático designado "DAGA – Damage Assessment Graphic Analyser" (DAGA). Através da inserção de um editor gráfico o programa permite a visualização 3D das anomalias existentes no betão e armaduras (perda de materiais e modificação das propriedades dos materiais). Esta ferramenta permite a análise e visualização das envolventes da capacidade resistente para diversos casos de carga e para diversos cenários de anomalias. Mediante a utilização programa DAGA foram efectuados estudos paramétricos (comportamento estático) e os seus resultados foram coligidos numa base de dados a ser posteriormente usada modelos de inteligência artificial. Para o efeito desenvolveu, ainda, um programa de cálculo designado por "ANACONDA – ANAlisys of CON crete DAmages" baseada na tecnologia de redes híbridas com componentes analíticas e neuronais incorporadas. Finalmente, são apresentadas as principais conclusões e a recomendação de futuras linhas de investigação neste campo.
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Hua, Wen-Gang. "Procedures for diagnosis and assessment of concrete buildings." 1993. http://web4.library.adelaide.edu.au/theses/09PH/09phh8737.pdf.
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Chiu, Chin-Lung, and 邱進隆. "A Synthetic Aperture Focusing Technique for Imaging Defects inside the Reinforced Concrete Element." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/24808746724068965750.
Full textAbstract:
博士國立中央大學
土木工程學系
101
This study combined with the transient elastic wave propagation theory and the synthetic aperture focusing technique (SAFT) to develop a method for imaging the defects inside the reinforced concrete structure. In the study, the finite deference method was used to simulate the stress wave propagation behavior in the concrete specimen with embedded defects and verified the results by the experiment. For most of the existing elastic-wave-based nondestructive testing methods, it is hard to detect defects inside reinforced concrete elements owing to the complex signals reflected from rebars. Therefore, this study conferred the possibility for using SAFT to scan and image the defects inside the reinforced concrete. In the first, the time-velocity curves were used to get an image by SAFT. The numerical and experimental images also show nice results can be obtained either holes or cracks inside the absolute concrete specimens. Next, the influence of the rebar on quality of SAFT image was quantitatively analyzed by a serious of numerical simulations. The experimental results show good agreements with the quantitative analyzing results. Then, the time-frequency analysis was further used to transform the original time domain signals. After the transform, the instantaneous frequency can occur an obviously hopping in the non-continuous of the signals. According to the property of HT, the reflection signal can be highlighted and get better SAFT image. This study also brought up to a multi-directional many-dimensional inspection technique to improve problem of the defect information missing in the one-directional inspection and used image reconstruct technique to upgrade the integrity of defect image. The image quality (resolution and contrast) of SAFT quality was qualitative analyzed by elastic wave theory and finite deference. From the analysis results, It is shown that this newly developed an inspecting procedure for in situ detection is fairly good. Finally, a hardware system for detecting and imaging the defects inside the reinforced concrete based on the SAFT theory and operation procedure was developed. Due to the integration of the hardware control of graphical interface and the signal and image processing program, the total time for SAFT detection is dramatically reduced. The system can be more suitable for in situ non-destructive testing of the reinforced concrete.
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Chen, Yo-Gea, and 陳佑家. "Using the impact-echo transfer function to evaluate internal defects in concrete repairing." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/n6dyu3.
Full textAbstract:
碩士朝陽科技大學
營建工程系碩士班
93
This dissertation is a study to evaluate internal defects condition in repair of concrete using the impact-echo transfer function. Explore the transfer response of differ depth delaminations in the plate-like structures .In plate-like structures sush as bridge decks, slabs and infill walls in frames, cracking often occurs in the form of delaminations in the plane of the reinforcing bars. Thus in repair and rehabilitation of concrete structures is to determine the extent of cracking at first and after finishing the repair work, to determine the amplitude of delaminations full filled epoxy and evaluate internal defects condition of concrete. The different diameters of cracks may lead to different spectral amplitude corresponding to concrete layer. The experimental show results by the images of the different positions of the impact relative to the plane of the delamination. Thus it is possible to non-destructively evaluate the nuclear power station, reservoir dike or, prestressing force beam which is unfit for coring. The purpose of this study is as following. 1. Using numerical simulation to study the relationship between ratio of different horizontal crack’s length and depth and the spectral amplitude in transfer function. 2. Explore the amplitude of the different length delaminations in the plate-like structures. Using numerical simulation to obtain the relationship between ratio of horizontal delaminations’ W/H and the spectral amplitude in transfer function.Can project the size of horizontal delaminations is more large and it’s amplitude is more to approach the plate’s amplitude. The spectral amplitude of experimental results and numerical results show, the spectral amplitudes values of delaminations full filled epoxy is about half of the the spectral amplitudes values of delaminations unfull filled epoxy. The correlation is high. In waveform analysing,evaluate the 10cm depth of delaminations part filled epoxy 1cm.The spectral frequecy show, the condition of the 10cm depth of delaminations and the 10cm depth of delaminations part filled epoxy 1cm are similar. Experimental results show, the images of the different positions of the impact relative to the specimen, approach to the numerical simulation amplitudes. Take the experimental parameters into the previously developed equation for relating peak-amplitude to the thickness of a pure concrete plate without substrate layer. The predicted amplitude for the 5 cm-thick plate is 2.3779, which has 0.34% error to the average experimental amplitude, 2.3697
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Chen, Long-Cherng, and 陳隆盛. "An Investigation on the Improving Strategies for Fixing Defects in Recycled Asphalt Concrete Pavement." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/63448293418886347998.
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Lyu, Syuan-Jhih, and 呂軒志. "A Study on Engineering Properties with Impact Factors of Geopolymer and its Application on Repairing Concrete Defects." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/267n85.
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博士國立臺北科技大學
工程科技研究所
101
Repair materials are key factors for structure restoration projects. Currently, however, no corresponding standards or methods exist for evaluating repair effectiveness. The formation of geopolymer is similar to concrete; it has low carbon dioxide emissions, high early strength, good durability, low volume change rate, and can be used as a pressure-bearing filler material. Geopolymer possesses great developmental potential for concrete defect repairs and has received much attention in recent years as an environmentally friendly material. Based on the framework of experimental design, this study investigates the influence factors, engineering and adhesion properties of geopolymer. First, statistical regression analysis is used to clarify the interaction between geopolymer constituents, and to understand the relationships between compositions, microstructure characteristics and mechanical properties. Secondly, a simple mechanical model is proposed to describe the repair properties of geopolymer on concrete cracks. After a series of adhesion tests with different layered angles, the adhesion properties and re-failure features of geopolymer-concrete interface are defined. In addition, the simulations of distinct element method are utilized to grasp the interface adhesion behavior of geopolymer after repairing concrete defects. Study results indicate that OH- (M) is the primary influential factor in geopolymer mechanical properties, and has an interaction with SiO2 (mol). As the OH- concentration increases, the geopolymer’s apparent cohesion and extent of polymerization also increased. Different proportions of OH- and SiO2 can form different Q4 (nAl) coordination structures, subsequently causing differences in mechanical properties. In addition, stress and extent of polymerizations had a significant effect on the geopolymer failure model. Under uniaxial compression conditions, geopolymer exhibited brittle fracture characteristics. As confining pressure increases it gradually changed to a slightly ductility characteristic. For repair adhesion, proposed mechanical models may consider the adhesion characteristics after repairing concrete defects with geopolymer. Plotting the stress damage envelope of layered specimens according to interface strength parameters can determine the damage model under different stress conditions. The experiments also showed that adding coal fly ash and granulated blast furnace slag to geopolymer lead to optimal interface adhesion strength. The normal stiffness of the adhesion interface and normal stress has an exponential relationship. Overall, the repair effectiveness can achieve above 95% regardless of confining pressure. For numerical simulation, the distinct element method can accurately simulate the mechanical behavior and damage pattern of specimens with different geopolymer, mortar substrate, and repair layer angles under uniaxial compression experiment conditions. The simulated results all conformed to the experiment value. This study used experimental design and statistical analysis. For geopolymer mechanical properties and numerical simulation, the proposed multiple regression equation achieved a model reliability of above 80%, which possesses reference value and significance.
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Liu, Sung-Lin, and 劉松林. "Numerical and Experimental Study on applying Synthetic Aperture Focusing Technique to Test Cracks and Defects in Reinforced Concrete." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/17512009468205965826.
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碩士中華大學
土木工程學系碩士班
102
In this paper the capability of the Synthetic Aperture Focusing Technique (SAFT) in detecting and imaging the cracks in plain concrete and the voids in reinforced concrete were studied. This research first utilized the Finite Element models to simulate the response of the stress wave propagation of a plain concrete with horizontal and tilted cracks and of a reinforced concrete with void subjected to impacting forces. The response signals were analyzed with SAFT and the resultant images were presented so that the feasibility of applying this technique on scanning and revealing the cracks and voids embedded in reinforced concrete can be studied. Two experimental specimens are then constructed in this research to be impacted by steel balls of different sizes and analysis was conducted with SAFT imaging procedure. Finally the results from experiments and from numerical simulation were compared for the purpose of verification. It was revealed from numerical simulation and experimental verification that the resolution of the images would be affected by the wave length of the stress waves introduced by the impacts of different steel balls. If the wave length of the introduced stress waves is short, fine cracks in the specimen can be revealed, whereas if the wave length is long, the interfering of reinforced bars can be reduced so that the defective voids can be scanned and revealed. Finally the feasibility of rotating the surfaces for impacting tests for testing and revealing defects was studied.
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Zhao, J., T. Hu, R. Zheng, P. Ba, C. Mei, and Qichun Zhang. "Defect recognition in concrete ultrasonic detection based on wavelet packet transform and stochastic configuration networks." 2020. http://hdl.handle.net/10454/18325.
Full textAbstract:
YesAiming to detect concrete defects, we propose a new identification method based on stochastic configuration networks. The presented model has been trained by time-domain and frequency-domain features which are extracted from filtering and decomposing ultrasonic detection signals. This method was applied to ultrasonic detection data collected from 5 mm, 7 mm, and 9 mm penetrating holes in C30 class concrete. In particular, wavelet packet transform (WPT) was then used to decompose the detected signals, thus the information in different frequency bands can be obtained. Based on the data from the fundamental frequency nodes of the detection signals, we calculated the means, standard deviations, kurtosis coefficients, skewness coefficients and energy ratios to characterize the detection signals. We also analyzed their typical statistical features to assess the complexity of identifying these signals. Finally, we used the stochastic configuration networks (SCNs) algorithm to embed four-fold cross-validation for constructing the recognition model. Based upon the experimental results, the performance of the presented model has been validated and compared with the genetic algorithm based BP neural network model, where the comparison shows that the SCNs algorithm has superior generalization abilities, better fitting abilities, and higher recognition accuracy for recognizing defect signals. In addition, the test and analysis results show that the proposed method is feasible and effective in detecting concrete hole defects.
This work was supported in part by the Zhejiang Provincial Natural Science Foundation (ZJNSF) project under Grant (No. LY18F030012), the National Natural Science Foundation of China projects (NSFC) under Grant (No. 61403356, 61573311).
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JHANG, YOU-BIN, and 張祐賓. "Use of Synthetic Aperture Focusing Technique to Detect the Defects in Concrete Specimen with Single Void and Single Layer∕ Double Layers Rebars." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/48896472840613747925.
Full textAbstract:
碩士中華大學
土木工程學系碩士班
100
The testing constraints and the capability of using the Synthetic Aperture Focusing Technique (SAFT) to detect void defects embedded in concrete block subjected to different introduced stress wave lengths and rebars are studied in this paper. This study first used the numerical simulation of finite elements to study the effects of the sizes of the impacting steel balls, the rebars and the layers of rebars on the testing responses. The testing results were processed with the Synthetic Aperture Focusing Technique and presented in images so that the direct effects of various kinds of parameters can be assessed. The study also cast concrete specimen with single void and single layer and double layers of rebars. Impact-response tests were carried out and the results were compared with those from numerical simulation. The results from the numerical simulation and experiments revealed that the sizes of the impacting steel balls would directly affect the resolution of the images from the SAFT. It was also found that the effect of existing rebars on the testing signals can be neglected when the wave length of the introduced stress waves is larger than eight to ten times of the size of the rebars. In this condition, the specimen can be regarded as uniform material and thus the results of evaluating the void defects would not be affected by the size of aggregates. Through this study, it is hoped that the capability of application of the SAFT can be enhanced in scanning and detecting the defects embedded in concrete structures.
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Huang, ZiRan, and 黃自然. "Defect Detection of Heavily Reinforced Concrete Plate." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/42835355029343350811.
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Lin, Juin Hann, and 林君翰. "Defect Detection of Large Scale Concrete Plate Using Spectral Imaging Method." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/00137922020272293146.
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Moufti, Sami. "A Defect-Based Approach for Detailed Condition Assessment of Concrete Bridges." Thesis, 2013. http://spectrum.library.concordia.ca/978014/1/Moufti_MASc_S2014.pdf.
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Bridge condition assessment is one of the most essential elements of Bridge Management Systems (BMS). This is owing to the fact that available inputs from assessment reports are constantly interpreted for maintenance decisions and budget allocation to critical bridges within a region’s inventory. Thus, performing effective bridge assessment is vital to ensure safety and sustainability of the bridge infrastructure. In practice, the evaluation of concrete bridges is mostly conducted on the basis of visual inspection, which is associated with considerable subjectivity and uncertainty inherent in human judgments. Additionally, current bridge assessment practices were found to be oversimplified, with conclusions being often drawn in absence of in-depth review and consideration of critical factors.
To remediate the existing shortcomings and ameliorate the bridge assessment process, this study proposes a fuzzy Hierarchical Evidential Reasoning (HER) approach for detailed condition assessment of concrete bridges under uncertainty. The essence of the suggested framework addresses the treatment and aggregation of uncertain measurements of detected bridge defects, in a systematic manner, to establish an enhanced platform for reliable and detailed bridge assessment. The significant features of this methodology can be summarized in the following points. First, the proposed approach utilizes a generic hierarchy that models the several levels of a concrete bridge under assessment; namely: bridge components, elements, and measured defects. Second, the proposed model is set to account for relative importance weights of all assessment factors in the hierarchical breakdown. Third, a novel HER assessment belief structure is employed to grip probabilistic uncertainty (ignorance) in bridge evaluation, whereas fuzzy uncertainty (subjectivity) is processed through a set of collectively exhaustive fuzzy linguistic variables. Forth, Dempster-Shafer (D-S) theory is eventually applied under the proposed HER framework for the purpose of accumulating supporting pieces of evidence in a comprehensive manner. The suggested model is implemented to arrive at detailed and informative bridge element condition ratings through data acquired from two case study bridges in Canada. As it benefits from a data oriented and structured algorithm, the developed defect-based model is believed to introduce a great deal of objectivity in an otherwise subjective area of infrastructure assessment. This falls within the ultimate goal of enhancing overall public safety and well-being.
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(11178285), Jose Capa Salinas. "An Unmanned Aerial Systems Evaluation Chamber for Bridge Inspection." Thesis, 2021.
Find full textAbstract:
Civil engineering structures must provide an adequate and safe performance during their time of service, and the owners of these structures must have a reliable inspection strategy to ensure time-dependent damage does not become excessive. Visual inspection is the first step in every structural inspection; however, many elements in the majority of structures are difficult to access and require specialized personal and equipment. In an attempt to reduce the risk of the inspector and the cost of additional equipment, the use of Unmanned Aircraft Systems (UAS) has been increasing in the last years. The absence of standards and regulations regarding the use of UAS in inspection of structures has allowed the market to widely advertise Unmanned Aerial Vehicles (UAV) without protocols or qualifications that prove their effectiveness, leaving the owners of the structures to solely rely on claims of the vendors before deciding which technology suits their particular inspection needs. Focusing primarily on bridge inspection, this research aimed to address the lack of performance-based evaluation and standards for UAS, developing a validation criterion to evaluate a given UAS based on a repeatable test that resembles typical conditions in a structure.
Current applications of UAS in inspection of structures along with its advantages and limitations were studied to determine the current status of UAS technologies. A maximum typical rotor-tip-to-rotor-tip distance of an UAV was determined based on typical UAVs used in bridge inspection, and two main parameters were found to be relevant when flying close to structures: proximity effects in the UAV and availability of visual line of sight. Distances where proximity effects are relevant were determined based on several field inspections and flights close to structures. In addition, the use of supplementary technologies such as Global Positioning System (GPS) and Inertial Measurement Units (IMU) was studied to understand their effect during inspection.
Following the analysis, the author introduces the idea of a series of obstacles and elements inside an enclosed space that resemble components of bridge structures to be inspected using UAVs, allowing repeatability of the test by controlling outside parameters such as lighting condition, wind, precipitation, temperature, and GPS signal. Using distances based on proximity effects, maximum typical rotor-tip-to-rotor-tip distance, and a gallery of bridges and situations when flying close to bridge structures, a final arrangement of elements is presented as the evaluation chamber. Components inside the evaluation chamber include both “real” steel and concrete specimens as well as those intended to simulate various geometric configurations on which other features are mounted. Pictures of damages of steel and concrete elements have been placed in the internal faces of the obstacles that can be assessed either in real-time flight or in post-processing work. A detailed comparison between the objectives of this research project and the results obtained by the evaluation chamber was performed using visual evaluation and resolution charts for the images obtained, the availability of visual line of sight during the test, and the absence of GPS signal.
From the comparison and analysis conducted and based on satisfactory flight results as images obtained during flights, the evaluation chamber is concluded to be a repeatable and reliable tool to apply to any UAS prior to inspect bridges and other structures, and the author recommends to refrain from conducting an inspection if the UAS does not comply with the minimum requirements presented in this research work. Additionally, this research provided a clearer understanding of the general phenomenon presented when UAVs approach structures and attempts to fill the gap of knowledge regarding minimum requirements and criterion for the use of UAS technologies in inspection of structures.
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Liu, Chien-Wei, and 劉建緯. "The Study of Methodologies of Defect and Maintenance on the Concrete Bridge Piers." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/78295932504710153897.
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Chen, Wei-Chun, and 陳維珺. "The preliminary study of using the dispersive velocities of Lame waves to detect the quality of concrete plate and interior defect of concrete." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/80673749043955053938.
Full textAbstract:
碩士朝陽科技大學
營建工程系
103
The purpose of this research is on detecting flaw inside concrete slab structure using the characteristics of Lamb waves generated by an impacting force applying on the surface. The experiments were conducted by one excitation source and one receiver configuration. The dispersion curves of the test results were obtained by short-time Fourier transform spectrum and amplitude reassigned method. The dynamic FEM is used for modeling concrete slab containing hole or honeycombs. The slowness dispersion diagrams for the responses obtaining from different source and the receiver distances were compared with the theoretical solution obtained by DISPERSE. The concrete slab containing defects (Honeycomb, Styrofoam blocks, acrylic panels, empty tube) were cast for conducting the experiments and the test results were analyzed and compared to the numerical ones. When the impactor-receiver distance is 0.5 m and hitting directly above the defect or the defect located beneath the survey line, the velocity will begin to decline at the wavelength about 2 times the thickness of concrete above the defect. For the impactor-receiver distance is 1.0 m and 1.5 m, the lower in velocity is not obvious. For a honeycomb under the survey line, regardless impactor-receiver distance, 0.5 m, 1.0 m or 1.5 m, the reduction of wavespeed for various wavelength were found. Numerical simulations show that for no defect cases the S_0 symmetrical mode is obvious for shorter impactor-receiver distance. As the distance stretched, S_0 symmetric modes will gradually disappear and A_0 anti-symmetric modes will be more significant. The better A0 signal can be achieved at a minimum distance 8 times the slab thickness. Result of defect cases show that the best distance of 1.0 m. The wavelength - velocity figures show the defects can affect the changes of velocity w.r.t. wavelength and the consistent flexural vibration of the thin layer of the concrete above the hole is more significant for the cases with larger impact-receiver distance.
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Ke, Fong-Jhang, and 柯烽章. "Using 3D Contour of Lamb Wave Group Velocity to Visualize the Interior Defect of Concrete." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/fu2bwr.
Full textAbstract:
碩士朝陽科技大學
營建工程系
106
The purpose of this research is on detecting flaw inside concrete slab structure using the characteristics of Lamb waves generated by an impacting force applying on the surface. The experiments were conducted by one excitation source and one receiver configuration. The dispersion curves of the test results were obtained by short-time Fourier transform spectrum and amplitude reassigned method. In order to explore the integrity of the concrete structure, MATLAB codes were designed to filter the A0 modal dispersion response of the reassigned spectrogram calculated from the experimental displacement waveform and then displayed as the velocity profile w.r.t. wavelength. The wave velocity profile of each measuring line on the test specimen were assembled to establish a 3D wave velocity contour images and compared to the defect layout of the specimens. The results of 3D images show clear image velocity drop for delaminated cracks, honeycombs, surface cracks, depth of the top motar layer for the mortar-concrete composite plate and distribution of grout within the prestressed tendon duct inside a concrete plate. Using 3D wave velocity imaging can speedily coarse identify the defect areas. And then refined test lines or other methods can be performed to locate the defective area more accurately. Besides, the 3D images obtained from gridded test lines can help the situation when single velocity profile can not be easily interpretated, as the averaging the velocity on the test points crossed by different test lines can improve the correctness of the local velocity. The results of single velocity profile show the defect depth and wavelength ratio is about 1.6 to 2.3 times of the wavelength at the velocity turning point. The results is not far from the theoretical turning point for a plate with the thickness the same as the defect depth which is about 2 times of the thickness. From the mortar-concrete composite plate with the thicknesses of the upper layer 0.03 m and 0.05 m the turning point at the wave length 1.6 to 2 times of the plate thickness can be observed. with the 3D profile one can improve the situation where the thickness of the weak layer can harder be identified for the cases with thinner top layer. For the specimens with upright wall contained prestressed ducts with different filling situation and testing on the wall containing duct at the depth 0.06 m with test line length of 0.6 m, the experimental results showed that the filling condition inside the duct can be observed from the rise or fall of the wave velocity. For test on the wall with the ducts 0.24 m away from the surface, measured line length 0.6 m and 0.9 m is chosen, the overall data and 3D image showed 0.9 m better than 0.6 m. The deeper void require longer impactor-receiver distance. The unfilled situation can more clearly observed for the 3D image obtained from the testing grids parallel to the ducts than those obtained from the two-way grid. The local 3D imaging results which were obtained from test lines directly above the duct clearly showed the internal variation of the filling situation.
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Kirlangic, Ahmet Serhan. "Condition Assessment of Cemented Materials Using Ultrasonic Surface Waves." Thesis, 2013. http://hdl.handle.net/10012/7696.
Full textAbstract:
Mechanical waves provide information about the stiffness and the condition of a medium; thus, changes in medium conditions can be inferred from changes in wave velocity and attenuation. Non-destructive testing (NDT) methods based on ultrasonic waves are often more economical, practical and faster than destructive testing. Multichannel analysis of surface waves (MASW) is a well-established surface wave method used for determination of the shear-wave profile of layered medium. The MASW test configuration is also applicable to assess the condition of concrete elements using appropriate frequency range. Both attenuation and dispersion of ultrasonic waves can be evaluated by this technique.
In ultrasonic testing, the characterization of a medium requires the precise measurement of its response to ultrasonic pulses to infer the presence of defects and boundary conditions. However, any ultrasonic transducer attached to a surface affects the measured response; especially at high frequencies. On the other hand, ultrasonic transducers available for engineering application are mostly used to measure wave velocities (travel time method). Therefore, these transducers do not have a flat response in the required frequency range. Moreover, in the case of full-waveform methods, the recorded signals should be normalized with respect to the transfer functions of the transducers to obtain the real response of the tested specimen.
The main objective of this research is to establish a comprehensive methodology based on surface wave characteristics (velocity, attenuation and dispersion) for condition assessment of cemented materials with irregular defects. To achieve the major objective, the MASW test configuration is implemented in the ultrasonic frequency range. The measured signals are subjected to various signal processing techniques to extract accurate information. In addition, a calibration procedure is conducted to determine the frequency response functions (FRF) of the piezoelectric accelerometers outside their nominal frequency range. This calibration is performed using a high-frequency laser vibrometer.
This research includes three main studies. The first study introduces the calibration approach to measure the FRFs of the accelerometers outside of their flat frequency range. The calibrated accelerometers are then used to perform MASW tests on a cemented-sand medium. The original signals and the corrected ones by eliminating the effect of the FRFs are used to determine material damping of the medium. Although, the damping ratios obtained from different accelerometers are not same, the values from the corrected signals are found closer to the characteristic damping value compared to those from the uncorrected signals.
The second study investigates the sensitivity of Rayleigh wave velocity, attenuation coefficient, material damping and dispersion in phase velocity to evaluate the sensitivity of these characteristics to the damage quantity in a medium. The soft cemented-sand medium is preferred as the test specimen so that well-defined shaped defects could be created in the medium. MASW test configuration is implemented on the medium for different cases of defect depth. The recorded signals are processed using different signal processing techniques including Fourier and wavelet transforms and empirical mode decomposition to determine the surface wave characteristics accurately. A new index, ‘dispersion index’, is introduced which quantifies the defect based on the dispersive behaviour. All surface wave characteristics are found capable of reflecting the damage quantity of the test medium at different sensitivity levels.
In the final study, the condition assessment of six lab-scale concrete beams with different void percent is performed. The beam specimens involving Styrofoam pellets with different ratios are tested under ultrasonic and mechanical equipment. The assessment produce established in the second study with well-defined defects is pursed for the beams with irregular defects. Among the characteristics, attenuation, P and R-wave velocities and dispersion index are found as the promising characteristics for quantifying the defect volume.
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Lan, Tung-Yen, and 藍棟彥. "Image Segmentation Implemented with Multilayer Level Set Applied on Infrared Thermal Images to Detect the Defectors Located in A Concrete Structure Covered with Carbon Fiber Reinforced Polymers." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/15075900807124960108.
Full textAbstract:
碩士朝陽科技大學
營建工程系碩士班
97
This paper utilizes the multilayer level set method for identification of surface defects within a material, through the examination of temperature variations within the material. Even though several image processing techniques have been proposed and applied to thermal images for non-destructive detection of surface defects, efficient and accurate detection of locate surface defects from thermal images is difficult. Mumford and Shah proposed to divide an image in a set of homogeneous sub-regions such that the energy contained in the image can reach its minimization. Based on this minimization of the energy, the multilayer level set method implicitly presents the regional boundaries as several nested level lines. By increasing iterations and preselected level values, these lines evolve close to the level boundaries based on the energy minimization. In this paper, we design an experiment in which the artificial defectors are buried behind and near the surface of a structure covered with Carbon Fiber Reinforced Plastic (CFRP). Then, a set of halogen lights are used to heat the structure. A thermal camera with temperature resolution 0.1 degrees Celsius is employed to record the temperature changes. The experimental results show that, according to the predefined level values, the multilayer level set method can successfully detect the regional boundaries of the buried defects by isolating the temperature changes within their neighborhoods from the given infrared thermal images.