جستجوی مقالات مرتبط با کلیدواژه « ebr » در نشریات گروه « عمران »

One of the most important applications of FRP sheets is the flexural strengthening of concrete beams by bonding these materials to the beam's tensile surface. The most common problem in this strengthening method is the early debonding of the sheet from the surface of the concrete, which results in a early failure before the final strength of the beam is obtained. The most common method for preparing concrete surfaces for proper bonding of composite sheets is the Externally Bonded Reinforcement (EBR) method, which, in addition to environmental pollution, does not completely eliminate the problem of early debonding of FRP sheet. This paper examines the possibility of replacing the proposed drilling method with mounting screws instead of EBR method. In this research, 10 samples of beam with dimensions of 150 × 300 × 1700 mm were tested under 4-point bending. The samples were tested by changing the number of layers and the method of mounting the sheets and in three samples with Simultaneous flexural and shear strengthening. Using the proposed method, the debonding problem was completely eliminated in all samples. The greatest increase in flexural strength was related to the sample, which, simoltanously strengthened in shear with FRP bars by NSM method.The effect of removing the bond in the middle part of the frp sheats was also investigated. The installation without bond of the sheets in the middle part, in addition to delaying the rupture of the sheets, increased the ductility.

The bond strength between fiber reinforced polymer (FRP) laminates and concrete is the main factor affecting the behavior of concrete members strengthened by externally bonded reinforcement (EBR) method. The bond strength depends on several factors, such as surface preparation, concrete strength, FRP stiffness and thickness and effective bond length. According to previous studies, using a bond length longer than the effective bond length, will not increase the connection load carrying capacity. Most existing theoretical models estimate bond strength based on the effective bond length. So, in order to achieve a satisfactory connection, it is important to determine the accurate value for the effective bond length of the lap joint. In this study, in order to evaluate and compare the effective bond length of fiber implantation method and the conventional EBR method, 12 concrete specimens were prepared and tested. Then, the effective bond length and the bond strength of the specimens were obtained by using single-shear pull test and using particle image velocimetry (PIV) method and compared with the existing specifications such as ACI and fib. The results showed that, using fiber implantation method instead of the conventional EBR method, would reduce the effective bond length by 20% and increase the bond strength between FRP and concrete substrate by 34%.

Externally Bonded Reinforcement (EBR) is known as a conventional method for flexural strengthening of concrete beams with Fiber Reinforced Polymer (FRP) composites. The present study has been conducted to investigate the flexural behavior of RC beams strengthened by CFRP sheets. Eight beam specimens strengthened by EBR method having the cross sectional dimensions of 250*300 mm and length of 2200 mm with two different reinforcement ratios (low and high) were evaluated under four point bending test. The compressive strength of four specimens was 25 MPa and other four specimens were made using high strength concrete with the compressive strength of 55 MPa. Additionally, the tensile reinforcement arrangement varied in different specimens with two bar sizes. In order to strengthen the specimens, two CFRP layers with dimensions of 160*1700 were used. Based on the results of the present study, in the case of low reinforcement ratio while maintaining the total reinforcement ratio constant, by decreasing the bar size and increasing the number of bars, the load carrying capacity of the specimen increases. In contrast, in the case of high reinforcement ratio, this results in the decrease of load carrying capacity. Finally, utilizing the smaller bar size in the tensile region of the specimens with low reinforcement ratio results in a more uniform distribution of cracks in the beam.

Various researches have been performed regarding the deterioration and behavior of fabrics made from carbon, glass and aramid in different environmental conditions. Carbon fibers reinforced polymer (FRP) are very corrosion resistant. The CFRP laminates are extremely useful in very corrosive atmospheres, such as marine and aggressive chemical atmospheres. They have been advanced over the years because of their high strength, light weight, long-term durability and high resistance to deterioration. The very thin (0.2 - 0.4 mm) laminates are very easy to apply and can be applied in cross directions without any difficulty. Environmental conditions impact on the bond strength of FRP-to-concrete has sparsely been investigated. The sources of CFRP bond deterioration can originate from alkaline attack and thermal expansion. Alkaline attack occurs at the interface of the concrete and a CFRP laminates with the resulting damage to the matrix of the CFRP laminates. Also, alkali aggregate reaction can lead to the destruction of concrete elements. However, studies in this field are not enough and for externally bonded FRP materials, no such long term test results are available yet. Severe corrosion damage can often be prevented by a correct treatment of the structure against chemical influences or aggressive environmental effects. Methods such as the externally bonded reinforcement (EBR), despite of their advantages, have a problem known as the premature debonding of FRP from concrete substrate. In this method the surface of concrete is sanded and cleaned. After the preparation of the surface, the layer of epoxy is applied uniformly on the surface of concrete. Then, FRP is installed on the surface and saturated with epoxy. In other hand, a new strengthen method is the externally bonded reinforced on grooves (EBROG) method that consists of grooves on the surface of concrete. In this method, grooves with a proper length, width and depth are catted on the concrete surface; then the concrete surface and the grooves are cleaned with an air pressure. Later, grooves are filled with an appropriate epoxy. At the end, FRP sheets are installed with a proper epoxy on the concrete surface. In this paper, the effect of environmental conditions, including three alkaline environments with temperatures of 〖 23〗^° C, 〖40〗^° C and 〖60〗^° C, was investigated on the bond strength of FRP-to-concrete. The specimens were strengthened with two EBR and EBROG. Samples were kept in environmental conditions for 3000 hours. Single-shear tests were conducted to evaluate the bond behavior of FRP-to-concrete. Experimental results showed that the specimens strengthened by the EBROG method - in the alkali environment with different conditions - experienced up to 50 % higher than ultimate bond loads compared with the specimens which were strengthened by the EBR method. In the EBR method, the bond failure mode changed from concrete delamination in laboratory condition to epoxy-concrete interface separation in alkali immersion with different temperatures. On the other hand, in the EBROG method environmental conditions had not effect on the mode of failure and more than 90% of specimens experienced FRP rupture. As a whole, the alkali environment caused a sudden drop in the bond strength of FRP-to-concrete substrate.