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Textile-reinforced mortar (TRM) is a strengthening material in which textiles are attached to reinforced concrete (RC) structures using an inorganic matrix. Although many studies on structural behavior, various factors that affect TRM behavior could not be determined clearly. Especially, the uncertainty in bonds due to inorganic materials was not considered. In this study, the flexural behavior of TRM-strengthened beams was determined considering intermediate crack debonding occurred. The TRM beam strengthening limit and TRM coefficients were defined considering the possibility of premature failure and experimental results of four other research on 22 specimens. Therefore, it is expected that a conservative design would be possible when the suggested strengthening limit coefficient is applied.

In this study, nine specimens were experimentally tested to analyze the strengthening efficiency of textile-reinforced mortar (TRM) and the difference in flexural behavior between prestressed and non-prestressed TRM-strengthened reinforced concrete beam. The test results show that TRM strengthening improves the flexural strength of TRM-strengthened reinforced concrete beams with alkali-resistant-(AR-) glass textile as well as that with carbon textile. However, in the case of textile prestressing, the strengthening efficiency for flexural strength of the AR-glass textile was higher than that of the carbon textile. The flexural stiffness of AR-glass textiles increased when prestressing was introduced and the use of carbon textiles can be advantageous to reduce the decreasing ratio of flexural stiffness as the load increased. In the failure mode, textile prestressing prevents the damage of textiles effectively owing to the crack and induces the debonding of the TRM.

The modular structure has a discontinuity owing to the joint between the modules, thus, structural behavior verification is required. In this study, the tensile behavior of a steel reinforcement at the discontinuity interface was evaluated in the joint of a modular flexural member. The modular specimen was fabricated with a 400 mm joint, and an integral specimen was fabricated with the same specifications as the modular specimen, without a joint. The largest crack width of the integral specimen was measured at the center of the beam, and that of the modular specimen was measured at the discontinuity interface. The maximum crack width of the modular specimen was greater than that of the integral specimen. The strain of the steel reinforcement was estimated using the measured crack width and six formulas for evaluating the crack width. The estimated strain of the modular specimen was higher than that of the integral specimen, and the deformation of the steel reinforcement at the discontinuity interface was accelerated with the increasing load. Therefore, the tensile load was concentrated at the discontinuity interface in the modular specimen, and the steel reinforcement at the discontinuity interface was likely to yield earlier than the integral specimen.

The effects of various prestressing levels on the flexural behavior of concrete beams strengthened with prestressed near-surface-mounted (NSM) carbon-fiber-reinforced polymer (CFRP) bars were investigated in this study. Four-point flexural tests up to failure were performed using a total of six strengthened prestressed and nonprestressed concrete beams. The nonprestressed strengthened beam failed by premature debonding at the interface of concrete and the epoxy adhesive, but the prestressed one failed owing due to rupture of the CFRP bar. As the prestressing level of the CFRP bar increased, the cracking and yield loads of the prestressed beams increased, but its effect on their deflections was insignificant. The ultimate load was constant regardless of prestressing level, but the ultimate deflection was almost inversely proportional to the level.

Cyclic loading tests were performed to investigate the energy dissipation capacities of reinforced concrete (RC) beams strengthened with carbon-fiber-reinforced polymer (CFRP) strips. Four RC beams were manufactured and three-point loaded. Responses of the strengthened beams to the cyclic loadings were measured, including deflections at the center of their span and strains of the CFRP strips and reinforcing steel rebars. Based on test results, the energy dissipation capacity of the strengthened beams were evaluated in comparison with that of an unstrengthened control beam.

The effects of prestress levels on the flexural behavior of concrete beams strengthened with near-surface-mounted (NSM) fiber-reinforced polymers (FRPs) were experimentally evaluated. Eight beams were tested. Failure of the prestressed strengthened beams occurred because of concrete cover separations at one end of the carbon FRP (CFRP) plates. With increasing prestress levels, the cracking, yield, and ultimate loads of the beams increased. The effect on the deflection corresponding to the cracking and yield loads was not significant; however, the ultimate deflections were affected by prestressing. The recommended prestress level for the concrete beams was ≤50% of the CFRP rupture strength.

The effect of fiber-reinforced polymer (FRP) plates, to which a peel-ply was fastened to increase their bonding area, on the behavior of strengthened concrete beams was investigated. A total of six concrete beams were tested. For the FRP plates, aramid-fiber-reinforced polymer (AFRP) ones were used. The test variables included their surface treatment (smooth and deformed), the depth of removal of concrete cover (0 and 10 mm), and the number of the plates. Each beam was tested in four-point bending under displacement control up to failure. Based on the experimental results obtained, the effect of the peel-plied AFRP plates on the flexural behavior of the concrete beams was evaluated.

This study addresses the applicability and effectiveness of prestressed unbonded carbon-fiber-reinforced polymer (CFRP) for strengthening concrete beams. Three- and four-point flexural tests were conducted up to failure for 10 concrete beams. The cracking, yield, and experimental nominal loads of the prestressed strengthened beams increased with the prestress levels. However, the ultimate loads were similar regardless of the prestress level because beam failure was dominated by rupture of the CFRP plates. Based on the results, the recommended appropriate prestress level for securing the ductility of a prestressed strengthened beam is ≤40% of the tensile strength of the CFRP plate. POLYM. COMPOS., 38:2459–2471, 2017. © 2015 Society of Plastics Engineers

Prefabricated bridges inevitably contain joints that should be made structurally stable. This paper focuses on the materials and methods used to connect transverse joints for prefabricated concrete bridges. A total of nine specimens were fabricated for which prestressing has been introduced after grouting high-performance mortar (HPM), and another seven specimens for which high-strength concrete (HSC) has been placed after lap splicing. Static flexural and cyclic loading tests were conducted. The HPM series specimens performed better than the integrated specimen. The HSC series specimens showed similar static flexural behavior, but lower serviceability, to that of the integrated specimen.

In this study, a series of flexural tests were performed to evaluate the energy capacity and debonding strain of reinforced concrete beams strengthened with a carbon-fiber-reinforced polymer (CFRP). Seven reinforced concrete beams were fabricated and loaded up to failure in a three-point bending test. The type of CFRP laminate (plate or sheet), bonded length (1.44 or 2.16 m), and wrapping of the CFRP sheet were selected as the key test variables. The test results showed that beams strengthened with CFRP sheets were more effective than those strengthened with CFRP plates. The CFRP-strengthened beams showed an elastic energy greater than that of the control beam, but the opposite result was obtained for the plastic energy. The average debonding strains of the CFRP plates and sheets were 4309 and 11,649 μ, respectively, which corresponded to 21.5% and 77.1% of their respective ultimate tensile. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

With the improvement in the quality of steel materials, the issue of fatigue cracking has become more important for steel bridges than the failure of the material itself. In this study, the Pelikan-Esslinger method was used to determine the fatigue stress of an orthotropic steel deck. A parametric study was then conducted with the steel deck components as the parameters. Based on the results, the effect of the diverse components of the steel deck on the fatigue stress was analyzed.

An experimental investigation was conducted to evaluate the structural behavior and chloride penetration characteristic of reinforced concrete columns to which patch repair was applied. A total of 24 reinforced concrete columns were fabricated. Four repair materials, with different types and contents of admixtures, were selected. The contents of the three admixtures (silica fume, zeolite, and polymer dispersion) were 0%, 10%, and 15%, based on the weights of the admixture and cement. For the experimental methods, a chloride penetration test and an axial compression test were used. As a result of the experiments, compression failure occurred in the control column. For the repaired columns, however, interfacial failure was observed, as the concrete core and repair material were debonded. The repair material that showed the greatest effect was mortar, for which polymer dispersion was used as the admixture. The ultimate strength and the strain at ultimate strength of the column that was repaired with this mortar increased by 40% and 80%, respectively, compared to the control column. Furthermore, the repair mortars that were mixed with the admixture showed much lower chloride concentrations than the control column. In particular, the chloride concentration of the mortar that was mixed with 15% polymer dispersion decreased by 95%, in the section with a depth of 20–30 mm from the column surface.

This paper deals with the prediction of crack width for reinforced concrete structural members under pure bending. An analytical method is proposed to estimate the flexural crack width for reinforced concrete members. The proposed method utilizes conventional crack theory. Also, to consider stress conditions in tensile zone reinforced concrete members, a bond-slip relationship developed from axial tension tests was used. An analytical equation for the estimation of maximum crack width is formulated as a function of maximum bond stress. The validity, accuracy and efficiency of the proposed method are obtained by comparing the analytical results with the experimental data, and major design codes, as well as a number of analytical solutions. The analytical results presented in this paper indicate that the proposed method can effectively estimate the flexural crack width of reinforced concrete members under bending.

This research was performed to identify physical properties of polysulfide epoxy polymer concrete for ultra-thin bridge deck pavement, and improve domestic applicability. With the optimum mix ratio determined from mixing experiments of polymer concretes, compressive, flexural, and bond strength were tested to identify its strength properties along with the freezing-thawing resistance test to evaluate its durability in harsh environments. As a result, the tested polymer concretes showed excellent performance in strength and deflection characteristic and all tested strength satisfied the criteria of American Concrete Institute. Moreover, it had better performance under variable temperatures comparing to other existing pavement materials. By the results of freezing-thawing resistance test and strength measurement for specimens underwent the freezing-thawing process, it can be judged that there is no such problem to the concrete`s durability. In conclusion, the newly developed polymer concrete in this research has appropriate properties for use in ultra-thin pavement on bridge deck, and moreover it has superior applicability in comparison with former materials due to its improved temperature sensitivity.

While the extent of repair and rehabilitation of existing old concrete structures is rapidly increasing, a vast number of repaired and rehabilitated structures do not function properly during their remaining service life. Especially in the case of using heterogeneous repair materials, it is very important to maintain the bonding performance between materials and to prevent the interface failure under static and fatigue loads. This paper focuses on the experimental investigation of reinforced concrete (RC) slabs, repaired and reinforced with an alumina/polymer (AP) mortar and a prestressing (PS) strand in the tension zone, under static and fatigue loadings. The variables in this experimental study were the space of strengthening, the number of strands, and AP mortar thickness. Attention is concentrated on the overall load-carrying capacity, deflection, strains of reinforcing bars, and the efficiency of repaired and reinforced RC slabs. Test results showed that the deflection of the repaired and reinforced RC slabs was approximately 40% lower than that of control RC slabs. The initial and horizontal cracking loads of a RC slab with an AP mortar of thickness 30 mm in the static test were approximately the same as those of a RC slab with a 20-mm-thick one. In the fatigue test, the deflection, the strain of reinforcing bars at the midspan, and the maximum shear stress of the repaired and strengthened RC slab were about 40~70% lower than those of the control RC slab. Therefore, it can be concluded that RC slabs with an AP mortar and PS strands have a good strengthening efficiency under both static and fatigue loadings, thanks to the high bonding capacity of the AP mortar.

The paper deals with evaluation of the bond performance between a CFRP plate and concrete with respect to various compressive strengths of concrete and bond lengths of the CFRP plate as parameters. To consider stress conditions in the tensile zone of reinforced concrete (RC) structures, double-lap axial tension tests were conducted for eight specimens with CFRP plates bonded to concrete prisms. In addition, a simple linear bond-slip model for the CFRP plate/concrete joints, developed from the bond tests, was used. To verify the model proposed, a total of seven RC beams were strengthened with CFRP plates and tested in flexure employing various bond lengths, strengthening methods, and numbers of CFRP plates. A nonlinear finite-element analysis, with the bond–slip model incorporated in the DIANA program, was performed for the strengthened RC beams. Also, the results of flexural test and analytical predictions are found to be in close agreement in terms of yield and ultimate loads and ductility.

This paper shows a study carried out on the estimation of nominal flexural strength for CFRP-plated RC beams failed by intermediate crack debonding. A strength reduction factor is proposed to consider the effect of the intermediate crack debonding for the determination of nominal flexural strength. The proposed factor is derived from experimental data and utilizes the ratio of effective stress(or strain) in the CFRP plate to its ultimate strength(or strain) which is called effective strain model. An analytical equation for the estimation of the nominal flexural strength is formulated as a function of strength reduction factor. The validity, accuracy and efficiency of the proposed factor are established by comparing the analytical results with the experimental data, and the major design codes, as well as a number of factors given by researchers. The analytical results presented in this paper indicate that the proposed factor can effectively estimate the flexural nominal strength of CFRP-plated reinforced concrete beams failed by intermediate crack debonding.

A CFRP (Carbon Fiber-Reinforced Plastic) strengthening method being widely used to increase the load-carrying capacity of structures is very suitable for existing bridge structures. However, not only flexure and shear failures but also debonding failure might be additionally occured in reinforced concrete(RC) beams strengthened with the CFRP plates. The CFRP debonding failure would cause a brittle fracture of the beam. Therefore, health monitoring for the CFRP bonding condition is strongly required. In this study, a feasibility of the impedance-based damage detection method using PZT sensors was investigated through a series of experimental studies for realtime structural health monitoring(SHM) for the CFRP laminated concrete structures.

Carbon fiber reinforced polymer (CFRP) laminated concrete structures are used widely in a range of engineering fields because of their many advantages. However they always carry the risk of structural collapse initiated from the debonding conditions that might occur between the CFRP and concrete surface. This study employed an electro-mechanical impedance-based wireless structural health monitoring (SHM) technique by applying PZT ceramic patches to identify the debonding conditions of a CFRP laminated reinforced concrete beam. In the experimental study, the CFRP-reinforced concrete specimens were fabricated and the impedance signals were measured from the wireless impedance sensor node according to the different debonding conditions between the concrete and CFRP. Cross correlation (CC)-based data analysis was conducted to quantify the changes in impedance measured at the PZT patches due to the debonding conditions. The results confirmed that an impedance-based wireless SHM technique can be used effectively for monitoring the debonding of CFRP laminated concrete structures.

The present study was carried out to evaluate the microstructural properties of a friction stir welded AZ91 with CaO Mg alloy. For this work, friction stir welding (FSW) was performed at a tool rotation speed of 1250 rpm and a traveling speed of 32 mm·min−1. A network of intermetallic compounds (Al2Ca) was observed in the base metal (BM). In the stir zone (SZ), fine grains and intermetallic compound particles were formed due to dynamic recrystalization and mechanical stirring. The hardness profile showed that the hardness of the SZ was higher than that of the BM, probably due to the presence of fine grains and thermally stable intermetallic compounds.

The traditional ball shear test is not suitable for evaluating joint reliability under drop loading, since the applied test speeds, usually lower than 5 mm/s, are well below the impact velocity applied to the solder joint in a drop test. The present study expands recently reported research by investigating the effect of thermal aging on the joint strength and fracture mode of Sn-3.0Ag-0.5Cu ball grid arrays during high-speed shear testing, with a shear height of 50 μm and a shear speed ranging from 0.01 m/s to 3 m/s. The test specimens were aged at 393 K for 1000 h. After reflow, a (Ni,Cu)3Sn4 intermetallic compound (IMC) layer was observed at the solder/Ni-P interface and the thickness of the IMC layer was increased through the aging process. The shear strength increased with increasing shear speed. The fracture surface of the solder joints showed three different fracture modes according to the shear speed and aging time. The fracture mode changed from ductile fracture to brittle fracture with increasing shear speed.

In this study, a total of 13 FRP-strengthened reinforced concrete beams were tested in flexure and analyzed using the finite element method. The various variables included bonding or no bonding of the FRP, the anchorage system, the amount of prestressing, and the span length. The experiments consisted of one control beam, two non-prestressed FRP-bonded beams, four prestressed FRP-unbonded beams, four prestressed FRP-bonded beams, and two prestressed FRP-unbonded beams with different span lengths. All the beams were subjected to three-point and four-point bending tests under deflection control, with the loading, deflection and failure modes recorded to the point of failure. A nonlinear finite element analysis of the tested beams was also performed using the DIANA software; this analysis accounted for the nonlinear concrete material behaviour, the reinforcement, and an interfacial bond-slip model between the concrete and CFRP plates. The aim of this investigation was to study the flexural performance of reinforced concrete members strengthened using CFRP plates, employing different FRP bonding and prestressing methods. The failure mode of the prestressed CFRP-plated beams was not debonding, but FRP rupture. For the reinforced concrete members strengthened with externally bonded prestressed CFRP plates, debonding of the composite laminates occurred in two stages. After the debonding of the CFRP plates that occurred in the bonded cases, the behaviour of the bonded CFRP-plated beams changed to that of the unbonded CFRP-plated beams due to the effect of the anchorage system. The flexural test results and analytical predictions for the CFRP-strengthened beams were compared and showed very good agreement in terms of the debonding load, yield load, and ultimate load. The ductility of the beams strengthened with CFRP plates having the anchorage system was considered high if the ductility index was above 3.

For RC structures, long-term deformation occurs due to the inherent characteristics, which are creep and shrinkage. In terms of serviceability, it is important to limit deflection caused by the deformation to the allowable deflection. In the recent years, various repair and strengthening methods have been used to improve performance of the existing RC structures. One of the typical methods is FRP externally bonded method (EBR). Fiber reinforced polymer (FRP) has been used worldwide as repair and strengthening materials due to its superior properties. Besides, it has to offer improved strengthening performance not only under instantaneous load but sustained load. Therefore, accurate prediction method of deflection for the RC members externally bonded with FRP under sustained load is required. In this paper, three beams were fabricated. Two beams were externally strengthened with one of CFRP plate and GFRP plate respectively. Total three beams were superimposed under sustained load of 25 kN. During 470 days, deflections at midspan were obtained. Moreover, creep coefficients and shrinkage strains were calculated by using ACI- 209 code and CEB-FIP code. In order to predict the deflection of the beams, EMM, AEMM, Branson's method and Mayer's method were used. Through the experiment, it was found that the specimen with CFRP plate has the most flexural capacity and Mayer's method is the most precise method to predict total long-term deflections.

Thermo-mechanical reliability of the anisotropic conductive film (ACF) joints in relation with flip chip bonding forces was evaluated by thermal shock testing. Two kinds of main failure modes were detected after thermal shock testing: formation of a conduction gap between conductive particles and Au bump or Ni/Au-plated Cu pad, and delamination of the adhesive matrix from the plated Cu pad on the flexible substrate. The determination of the failure mode was mainly affected by the variation of the bonding force. The main failure mode of the thermally shocked ACF joints was conduction gap for the joints with low bonding forces and adhesive matrix delamination for the joints with high bonding forces. Finite element analysis was also performed to determine the stress distributions within the two kinds of flip chip packages having different bonding gaps when it was stressed by the temperature rising.

A novel indirect tensile test method, the biaxial flexure test (BFT) method, has been developed to measure the biaxial tensile strength of concretes. The classical modulus of rupture (MOR) test has been generalized to three dimensions. In this method, we use a circular plate as the new test specimen. This plate is supported by an annular ring. We apply an external load to this specimen through a circular edge. The centers of the specimen, the loading device and the support are identical. The biaxial tensile strength measured by this new method is about 19% greater than the uniaxial tensile strength obtained from the classical modulus of rupture test as reported by other researchers. However, at the same time, we also found that the stochastic deviation of the biaxial tensile strength is about 63% greater than the uniaxial strength.

The microstructure, mechanical properties and thermal stability of double friction stir welded 2219 Al alloy were investigated. The grain size of the double friction stir zone was about 0.8 mm, which was smaller than that of the single friction stir zone. The dissolution of the very fine strengthening particles resulted in a decrease of the hardness values in the single and double friction stir zone. Following the post weld heat treatment (PWHT), the grain structure of the double-FSW joints was found to be more unstable than that of the single-FSW joints, owing to the finer grain size, higher fraction of sub-grains and lower particle density. [doi:10.2320/matertrans.MRP2007249]

This paper discusses the failure mode of reinforced concrete beams strengthened with composite materials based on six experimental set-ups to determine the FRP-to-concrete bond strength. Interfacial bond behavior between concrete and CFRP plates was discussed. Shear test were performed with different concrete compressive strengths (21 MPa and 28 MPa) and different bonding length (100 mm, 150 mm, 200 mm, and 250 mm). Shear test results indicate that the effective bond length (the bond length beyond which the ultimate load does not increase) was estimated as 196~204 mm through linear regression analysis. Failure modeof specimens occurred due to debonding between concrete and CFRP plates. Maximum bond stress is calculated as about 3.0~3.3 MPa from the relationships between bond stress and slip. Finally, the interfacial bond-slip model between CFRP plates and concrete, which is governed debonding failure, has been estimated from shear tests. Average bond stress was about 1.86~2.04 MPa, the volume of slip between CFRP plate and concrete was about 1.45~1.72 mm, and the fracture energy was found to be about 1.35~1.71 N/mm.

Recently, concrete structures with carbon fiber reinforced polymer (CFRP) reinforcements have been commonly used for the bridge and building construction. In this paper, pier caps were strengthened by prestressed near surface mounted CFRP. To verify the effectiveness of the strengthening method, 7 pier cap specimens were fabricated. One specimen was designed for control, two for external prestressing steel strands, two for CFRP plates, and two for CFRP bars. Experimental variables consist of type of reinforcement materials and prestressing levels. The results of laboratory have shown that the ultimate load capacities of prestressed near surface mounted CFRP specimens were about greater than that of a control specimen. Also, ultimate load capacities of prestressed near surface mounted CFRP specimens were similar to those of external prestressing specimens with steel strands.

In this paper, a total of 13 beams with bonding, anchorage system, amount of prestressing and span length as variables of experiment were tested in flexural test and analyzed in finite element analysis; one control beam, two simplified FRP-boned beams, four prestressed FRP-unbonded beams and four prestressed FRP-bonded beams. Also, a nonlinear finite element analysis of beams in the flexural test is performed by DIANA program considered material nonlinear of concrete, reinforcement and the interfacial bond-slip model between concrete and CFRP plates. The failure mode of prestressed CFRP plated-beams is not debonding but FRP rupture. RC members strengthened with external bonded prestressed CFRP plates occurred 1st and 2nd debonding of the composite material. After the debonding of CFRP plates occurs in bonded system, behavior of bonded CFRP-plated beams change into that of unbonded CFRP-plated beams due to fix of the anchorage system. Also, It was compared flexural test results and analytical results of RC members strengthened with CFRF plates. The ductility of beams strengthened by CFRP plates with the anchorage system is considered high with the ductility index of above 3. Analysis results showed a good agreement with experiment results in the debonding load, yield load and ultimate load.

Ball shear test was investigated in terms of effects of important test parameters, i.e. shear height and shear speed, with an experimental and non-linear finite element analysis for evaluating the solder joint integrity of area array packages. A Pb-free solder composition was examined in this work: Sn-3Ag-6Bi-2In. The substrate was a common SMD (Solder Mask Defined) type with solder bond pad openings of 460㎛ in diameter. It could be observed that increasing shear height, at fixed shear speed, has the effect of decreasing shear force, while the shear force increased with increasing shear speed at fixed shear height. Too high shear height could cause some bad effects on the test results such as unexpected high standard deviation values or shear tip sliding from the solder ball surface. The low shear height conditions were favorable for screening the type of brittle interfacial failures or the degraded layers in the interfaces.

Ball shear test was investigated in terms of the effects of important test parameter, i.e., shear height, with an experimental and non-linear finite element analysis for evaluating the solder joint integrity of area array packages. The substrate was a common SMD type with solder bond pad openings of 460 ㎛ in diameter. It was observed that increasing the shear height, at a fixed shear speed, has the effect of decreasing the shear force. The high shear height could cause some bad effects on the test results such as unexpected high standard deviation values or shear tip sliding from the solder ball surface. The low shear height conditions were favorable for screening the type of brittle interfacial fractures or the degraded layers in the interfaces.

The repair and rehabilitation of structures have recently become of great concern due to an increase in loadings and the degradation of structures with time. Considerable efforts are still being undertaken to develop new construction materials. This experimental study describes the flexural behavior of reinforced concrete beams repaired by Polymer Cementitious Mortar and Cement Mortar in the tension zone. Preliminary trials in which beams tensile reinforcing steel was exposed over 100%, 80% and 60% of their length have led to tests on 15×25 cm beams over a 200 cm span. The test parameters of this experimental study, such as the ratio of tensile steel, repair materials and repair length, are discussed here. Emphasis is given to overall bending capacity, deflection, ductility index, failure mode and crack development of repaired beams.

The high-velocity oxygen fuel (HVOF) thermal spray is used for a particulate deposition process in which micro-sized particles are propelled and heated in a supersonic combusting gas stream. It is characterized by high gas velocity and high density and is being used in an increasing variety of coating applications, such as ceramic and composite coatings, to improve wear and abrasion resistance. The particle temperature and velocity are two of the most important parameters in HVOF thermal spraying, which affect the quality of the coatings. To understand the particle dynamics, it is necessary to study, first, the thermal flow characteristics in the HVOF system. In this study, a numerical analysis is performed to predict the gas dynamic behaviors, and the effect of the geometrical parameter is studied to optimize the nozzle design.

Many researches on behavior of the structures which were externally strengthened with FRPs have been conducted. However, researches on time-dependent behavior have not been conducted yet. In order to provide improved serviceability to reinforced concrete (RC) members strengthened with FRPs, the behavior of RC structures strengthened with FRPs under sustained loads should be investigated. This paper presents a series of long-term deflection, deformation-recovery and residual strength experiments. For the long-term experiments, three RC beams were fabricated and two of the beams were strengthened with a carbon FRP(CFRP) plate and a glass FRP(GFRP) plate respectively. The beams were placed under sustained load for about 550 days and unloaded. After unloading, static flexural experiments were carried out. As the result, CFRP showed better performance in terms of deflection and strains of rebars and CFRP plate. Moreover, CFRP showed higher deformation recovery and residual strength than the other beams.

Strengthening concrete structures with FRP(fiber reinforced polymer) have grown to be a widely used method over most parts of the world today, which FRP was developed in 1960's. A method to apply prestressing force to FRP is developed newly in these days, which can use the maximum performance of FRP materials. This study investigated the flexural behavior of simply supported Reinforced Concrete(R/C) beams strengthened with Prestressed Near Surface Mounted (NSM) CFRP(carbon fiber reinforced polymer) . CFRP plate and rod were used for flexural strengthening. Prestressing level changed from 0 % of CFRP tensile strength to 50 %. Any mechanical device has not been used to maintain the prestress during testing. Static four point loading tests are conducted for eleven R/C beams strengthened with Prestressed Near Surface Mounted (NSM) CFRP and Non-prestressed Near Surface Mounted (NSM) CFRP. The test shows that the beams with prestressed NSM CFRP exhibited a higher yielding load and a higher ultimate load, compared to the beams with non-prestressed NSM CFRP and the control beams. Beams strengthened by CFRP rod failed due to fiber rupture of the FRP in the groove, but beams strengthened by CFRP plate failed due to concrete cover separation.