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Saad Mahmood Raoof - One of the best experts on this subject based on the ideXlab platform.
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trm versus frp in flexural strengthening of rc beams behaviour at high temperatures
Construction and Building Materials, 2017Co-Authors: Saad Mahmood Raoof, Dionysios A BournasAbstract:The flexural behaviour of RC beams strengthened with TRM and FRP composites was experimentally investigated and compared both at ambient and high temperatures. The investigated parameters were: (a) the strengthening material, namely TRM versus FRP, (b) the number of strengthening layers, (c) the textile surface condition (dry and coated), (d) the textile material (carbon, basalt or glass fibres) and (e) the end-anchorage of the flexural reinforcement. A total of 23 half-scale beams were constructed, strengthened in flexure and tested to assess these parameters and the effectiveness of the TRM versus FRP at high temperatures. TRM exhibited excellent performance as strengthening material in increasing the flexural capacity at high temperature; in fact, TRM maintained an average effectiveness of 55%, compared to its effectiveness at ambient temperature, contrary to FRP which totally lost its effectiveness when subjected to high temperature. In specific, from the high temperature test it was found that by increasing the number of layers, the TRM effectiveness was considerably enhanced and the failure mode was altered; coating enhanced the TRM effectiveness; and the end-anchorage at high temperature improved significantly the FRP and marginally the TRM effectiveness. Finally, the formula proposed by the Fib Model Code 2010 was used to predict the mean Debonding Stress in the TRM reinforcement, and using the experimental results obtained in this study, a reduction factor to account for the effect of high temperature on the flexural strengthening with TRM was proposed.
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Bond between textile reinforced mortar (TRM) and concrete substrate
2017Co-Authors: Saad Mahmood RaoofAbstract:There is a growing interest for strengthening and upgrading existing concrete structures both in seismic and non-seismic regions due to their continuous deterioration as a result of aging, degradation induced environment conditions, inadequate maintenance, and the need to meet the modern codes (i.e. Eurocodes). Almost a decade ago, an innovative cement-based composite material, the so-called textile-reinforced mortar (TRM), was introduced in the field of structural retrofitting. TRM comprises high-strength fibres in form of textiles embedded into inorganic matrices such as cement-based mortars. TRM offers well-established advantages such as: fire resistance, low cost, air permeability, and ability to apply on wet surfaces and at ambient of low temperatures. It is well known that the effectiveness of any external strengthening system in increasing the flexural capacity of concrete members depends primarily on the bond between the strengthening material and member’s substrate. This PhD Thesis provides a comprehensive experimental study on the bond behaviour between TRM and concrete substrate and also provides a fundamental understanding of the flexural behaviour of RC beams strengthened with TRM. Firstly, the tensile properties of the textile reinforcement were determined through carrying out tensile tests on bare textiles, and TRM coupons. Secondly, the bond behaviour between TRM and concrete substrates both at ambient and, for the first time, at high temperature was extensively investigated. A total of 148 specimens (80 specimens tested at ambient temperature and 68 specimens tested at high temperatures) were, fabricated, and tested under double-lap shear. Parameters investigated at ambient temperature comprised: (a) the bond length; (b) the number of layers; (c) the concrete surface preparation; (d) the concrete compressive strength; (e) the textile surface condition; and (f) the anchorage through wrapping with TRM jackets. Whereas, the parameters examined at high temperatures included: (a) the strengthening systems (TRM versus FRP); (b) the level of temperature at which the specimens were exposed; (c) the number of FRP/TRM layers; and (d) the loading conditions. The results of ambient temperature tests indicated that the bond at the TRM-concrete interface is sensitive to parameters such as: the number of layers, the textile surface condition, and the anchorage through wrapping with TRM. On the other hand, the results of high temperature tests showed that TRM exhibited excellent bond performance with concrete (up to 400 0C) contrary to FRP which practically lost its bond with concrete at temperatures above the glass trainset temperature (Tg). The flexural strengthening of RC beams with TRM at ambient and for the first time at high temperature was also examined carrying out 32 half-scale beams. The examined parameters were: (a) the strengthening system (TRM versus FRP); (b) the number of layers; (c) the textile surface condition; (d) the textile fibre material; (e) the end-anchorage system of the external reinforcement; and (f) the textile geometry. The results of ambient temperature tests showed that TRM was effective in increasing the flexural capacity of RC beams but its effectiveness was sensitive to the number of layers. Furthermore, a simple formula used for predicting the mean FRP Debonding Stress was modified for predicting the TRM Debonding Stress based on the experiment data available. The results of high temperature tests showed that TRM maintained an average effectiveness of 55%, of its effectiveness at ambient temperature, contrary to FRP which has totally lost its effectiveness when subjected to high temperature. Finally, a Stress reduction factor of TRM flexural effectiveness (compared to its ambient effectiveness) when subjected to high temperature was also proposed.
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textile reinforced mortar trm versus fibre reinforced polymers frp in flexural strengthening of rc beams
Construction and Building Materials, 2017Co-Authors: L Koutas, Saad Mahmood Raoof, Dionysios A BournasAbstract:The aim of this paper is to compare the flexural performance of reinforced concrete (RC) beams strengthened with textile-reinforced mortar (TRM) and fibre-reinforced polymers (FRP). The investigated parameters included the strengthening material, namely TRM or FRP; the number of TRM/FRP layers; the textile surface condition (coated and uncoated); the textile fibre material (carbon, coated basalt or glass fibres); and the end-anchorage system of the external reinforcement. Thirteen RC beams were fabricated, strengthened and tested in four-point bending. One beam served as control specimen, seven beams strengthened with TRM, and five with FRP. It was mainly found that: (a) TRM was generally inferior to FRP in enhancing the flexural capacity of RC beams, with the effectiveness ratio between the two systems varying from 0.46 to 0.80, depending on the parameters examined, (b) by tripling the number of TRM layers (from one to three), the TRM versus FRP effectiveness ratio was almost doubled, (c) providing coating to the dry textile enhanced the TRM effectiveness and altered the failure mode; (d) different textile materials, having approximately same axial stiffness, resulted in different flexural capacity increases; and (e) providing end-anchorage had a limited effect on the performance of TRM-retrofitted beams. Finally, a simple formula proposed by fib Model Code 2010 for FRP reinforcement was used to predict the mean Debonding Stress developed in the TRM reinforcement. It was found that this formula is in a good agreement with the average Stress calculated based on the experimental results when failure was similar to FRP-strengthened beams.
Dionysios A Bournas - One of the best experts on this subject based on the ideXlab platform.
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trm versus frp in flexural strengthening of rc beams behaviour at high temperatures
Construction and Building Materials, 2017Co-Authors: Saad Mahmood Raoof, Dionysios A BournasAbstract:The flexural behaviour of RC beams strengthened with TRM and FRP composites was experimentally investigated and compared both at ambient and high temperatures. The investigated parameters were: (a) the strengthening material, namely TRM versus FRP, (b) the number of strengthening layers, (c) the textile surface condition (dry and coated), (d) the textile material (carbon, basalt or glass fibres) and (e) the end-anchorage of the flexural reinforcement. A total of 23 half-scale beams were constructed, strengthened in flexure and tested to assess these parameters and the effectiveness of the TRM versus FRP at high temperatures. TRM exhibited excellent performance as strengthening material in increasing the flexural capacity at high temperature; in fact, TRM maintained an average effectiveness of 55%, compared to its effectiveness at ambient temperature, contrary to FRP which totally lost its effectiveness when subjected to high temperature. In specific, from the high temperature test it was found that by increasing the number of layers, the TRM effectiveness was considerably enhanced and the failure mode was altered; coating enhanced the TRM effectiveness; and the end-anchorage at high temperature improved significantly the FRP and marginally the TRM effectiveness. Finally, the formula proposed by the Fib Model Code 2010 was used to predict the mean Debonding Stress in the TRM reinforcement, and using the experimental results obtained in this study, a reduction factor to account for the effect of high temperature on the flexural strengthening with TRM was proposed.
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textile reinforced mortar trm versus fibre reinforced polymers frp in flexural strengthening of rc beams
Construction and Building Materials, 2017Co-Authors: L Koutas, Saad Mahmood Raoof, Dionysios A BournasAbstract:The aim of this paper is to compare the flexural performance of reinforced concrete (RC) beams strengthened with textile-reinforced mortar (TRM) and fibre-reinforced polymers (FRP). The investigated parameters included the strengthening material, namely TRM or FRP; the number of TRM/FRP layers; the textile surface condition (coated and uncoated); the textile fibre material (carbon, coated basalt or glass fibres); and the end-anchorage system of the external reinforcement. Thirteen RC beams were fabricated, strengthened and tested in four-point bending. One beam served as control specimen, seven beams strengthened with TRM, and five with FRP. It was mainly found that: (a) TRM was generally inferior to FRP in enhancing the flexural capacity of RC beams, with the effectiveness ratio between the two systems varying from 0.46 to 0.80, depending on the parameters examined, (b) by tripling the number of TRM layers (from one to three), the TRM versus FRP effectiveness ratio was almost doubled, (c) providing coating to the dry textile enhanced the TRM effectiveness and altered the failure mode; (d) different textile materials, having approximately same axial stiffness, resulted in different flexural capacity increases; and (e) providing end-anchorage had a limited effect on the performance of TRM-retrofitted beams. Finally, a simple formula proposed by fib Model Code 2010 for FRP reinforcement was used to predict the mean Debonding Stress developed in the TRM reinforcement. It was found that this formula is in a good agreement with the average Stress calculated based on the experimental results when failure was similar to FRP-strengthened beams.
L Koutas - One of the best experts on this subject based on the ideXlab platform.
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textile reinforced mortar trm versus fibre reinforced polymers frp in flexural strengthening of rc beams
Construction and Building Materials, 2017Co-Authors: L Koutas, Saad Mahmood Raoof, Dionysios A BournasAbstract:The aim of this paper is to compare the flexural performance of reinforced concrete (RC) beams strengthened with textile-reinforced mortar (TRM) and fibre-reinforced polymers (FRP). The investigated parameters included the strengthening material, namely TRM or FRP; the number of TRM/FRP layers; the textile surface condition (coated and uncoated); the textile fibre material (carbon, coated basalt or glass fibres); and the end-anchorage system of the external reinforcement. Thirteen RC beams were fabricated, strengthened and tested in four-point bending. One beam served as control specimen, seven beams strengthened with TRM, and five with FRP. It was mainly found that: (a) TRM was generally inferior to FRP in enhancing the flexural capacity of RC beams, with the effectiveness ratio between the two systems varying from 0.46 to 0.80, depending on the parameters examined, (b) by tripling the number of TRM layers (from one to three), the TRM versus FRP effectiveness ratio was almost doubled, (c) providing coating to the dry textile enhanced the TRM effectiveness and altered the failure mode; (d) different textile materials, having approximately same axial stiffness, resulted in different flexural capacity increases; and (e) providing end-anchorage had a limited effect on the performance of TRM-retrofitted beams. Finally, a simple formula proposed by fib Model Code 2010 for FRP reinforcement was used to predict the mean Debonding Stress developed in the TRM reinforcement. It was found that this formula is in a good agreement with the average Stress calculated based on the experimental results when failure was similar to FRP-strengthened beams.
Jonghwan Suhr - One of the best experts on this subject based on the ideXlab platform.
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INVESTIGATION OF MECHANICAL DAMPING CHARACTERISTIC IN SHORT FIBERGLASS REINFORCED POLYCARBONATE COMPOSITES
Modern Physics Letters B, 2013Co-Authors: Myoung-rae Cho, Hyung-ick Kim, Jonghwan Suhr, Jae-soon Jang, Devin R. Prate, David ChunAbstract:The focus of this study is to experimentally investigate the effect of Debonding Stress, the interface between the fibers and the polymer matrix, on the damping properties of the short fiberglass reinforced polymer composites. In this study, short fiberglass reinforced polycarbonate composite materials were fabricated and characterized for their tensile properties by varying the fiberglass loading fraction. The Debonding Stress was evaluated by coupling the acoustic emission technique with the tensile testing. After the determination of the Debonding Stress was completed, dynamic cyclic testing was performed in order to investigate the effect of Debonding on the damping properties of the polymer composites. It was experimentally observed in this study that the Debonding can facilitate the stick-slip friction under cyclic loadings, which then gives rise to better damping performance in the fiberglass composites.
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Determination of local Debonding Stress and investigation of its effect on mechanical properties of glass short fiber reinforced polycarbonate composites
Behavior and Mechanics of Multifunctional Materials and Composites 2012, 2012Co-Authors: Wenjie Zhao, Hyung-ick Kim, Jonghwan SuhrAbstract:Thermoplastic polymers are often reinforced by adding short fibers to improve mechanical properties including Young's modulus and tensile strength of the polymers. In many engineering applications, energy absorbing characteristics in such particulate polymers is known to be a very important property to be considered in composite designs, and meanwhile Debonding at the interface between fiber and matrix in the composites may affect the energy absorption properties. Here, the focus of this study is to employ a semi-empirical approach to determine the Debonding Stress and investigate the effect of the Debonding Stress on energy absorbing properties of short glass fiber reinforced polycarbonate composites. Glass short fiber reinforced polycarbonate composites are fabricated via a solution mixing technique. Tensile testing and acoustic emission measurement are simultaneously performed for the polycarbonate composites. The test results including toughness are compared for the composites over neat polycarbonate. Also the local Debonding Stress in the vicinity of each glass fiber in composites is estimated by combining modeling and experiments. A finite element model is developed to determine local Debonding Stress at the interface between the fiber and matrix. The local Debonding Stress appears to considerably affect the toughness of the composites.
Bernd Lauke - One of the best experts on this subject based on the ideXlab platform.
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Contribution of matrix yielding energy to the crack resistance of particle reinforced composites
Composites Science and Technology, 2013Co-Authors: Bernd LaukeAbstract:Abstract The incorporation of particles into polymer matrix causes local Stresses in their neighbourhood when the composite is loaded. High multiaxial Stress fields are created in front of a crack which leads to various fracture processes in a region close to the crack tip. These processes contribute to the energy dissipation of the moving crack, increasing the crack resistance of the material. One of these processes is matrix yielding around particles after Debonding of the particles and that is considered in this paper. At first the crack resistance for this mechanism was obtained by integration over the Stress field within the dissipation zone. At second the mechanical problem of a spherical particle within a spherical elastic/perfectly plastic matrix under uniform radial tensile Stress was solved. After particle Debonding, the yielding energy of the matrix shell was calculated. Finally an analytical equation for the composite crack resistance for this mechanism was obtained, which is a function of mechanical properties of the components, particle volume fraction in the composite and local particle fraction. Debonding energy, matrix yield Stress and particle size come only into play if the Debonding Stress is larger than the minimum uniform Stress for yielding initiation.
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Effect of particle size distribution on Debonding energy and crack resistance of polymer composites
Computational Materials Science, 2013Co-Authors: Bernd LaukeAbstract:Abstract Crack resistance of particle reinforced polymers is affected by the size distribution of particles. Particle Debonding is a major dissipation mechanism that contributes itself and triggers other mechanisms such as matrix shear bands or plastic void growth. Assuming the specific Debonding energy at the particle/matrix interface as independent of particle size together with the Debonding criterion that depends on the particle size leads to analytical expressions that depend on the parameters of the particle size distribution function as well on the Debonding probability function. But numerical results show nearly constant crack resistance by changing mean particle size. Using instead a Debonding criterion with the supposition that Debonding Stress does not depend on particle size reveals that smaller particles increase facture toughness. The increase is significant for composites with particle size distribution functions that show small standard deviations. However, should the Debonding energy at the interface be proportional to the particle diameter then the crack resistance remains constant by changing particle size for both Debonding criteria.
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Single fibre transverse Debonding: Stress analysis of the Broutman test
Composites Part A: Applied Science and Manufacturing, 2000Co-Authors: T. Schüller, W. Beckert, Bernd Lauke, Christophe Ageorges, Klaus FriedrichAbstract:The paper presents an extended analytical approach for the interfacial transverse Stress that is generated by the Broutman test specimen under compression. The analysis is based on the division of the specimen into a bulk region and a near fibre region. Treating separately each region a compound equation for the interfacial Stress can be derived. The equation also includes residual thermal Stress and fibre anisotropy. A 3D finite element model was used to validate the approach. The calculations are performed for two commonly used material systems (carbon/glass fibre, epoxy resin). A comparison between the finite element results and the analytical solutions indicates that the accuracy of the analytical approach is very good.
