Abstract. Reinforced concrete beam is normally reinforced by steel bars to sustain tensile forces occurring due to flexural response, and vertical steel reinforcement to sustain shear stresses. On the other side, the truss system is a structure composed by triangle. Truss system develops its flexural capacity based on the inter-action of the bar elements. Therefore, introducing of the truss system to the reinforced concrete beams by modifying of the tensile and shear reinforcement may increase the beam flexural capacity. The study on the application of the truss system to the reinforced concrete beams has been conducted. The shear reinforcement was modified to form the triangles that were connected to the tensile reinforcement on the bottom and compressive reinforcement on the top. The steel bar elements were connected by welding to form a truss system. The effect of the buckling of the compression bar element on the truss system may be avoided due to the constrain effect of the surrounding concrete. In order to clarify the effect of the truss system reinforcement to the flexural behaviour, a series of specimens was prepared. The beams specimens have a length of 3.3 m with cross section of the 15 by 20 cm. A normal concrete beam was also prepared as control specimens. Results indicated that the concrete beams reinforced by truss system had flexural capacity higher than the normal beam.
Abstract-Fiber reinforced polymer (FRP) has been applied to many purposes for civil engineering structures not only for new structures but also for strengthening of the deteriorated structures. The application of FRPs in various forms such as rod, grid and sheet are widely accepted solution due to its corrosion resistance as well as high tensile strength to weight ratio. Glass composed FRP (GFRP) sheet is most commonly used due to its relatively lower cost compared to the other FRP materials. GFRP sheet is applied externally by bonding it on the concrete surface. Many studies have been done to investigate the bonding of GFRP sheet. However, it is still very rarely studies on the bonding behavior of GFRP sheet on the strengthened beams due to flexural loadings. This is important to be clarified for the wider application of GFRP sheet especially on the flexural structure such as highway bridge girders. This study presented the results of experimental investigation of the bonding behavior on the strengthened concrete beams due to flexural loadings. A series of concrete beams strengthened with GFRP sheet on extreme tension surface were prepared. Results indicated the bonding distribution along the GFRP sheet due to flexural loading tended to be non-linear. The bond stress due to flexural loading was lower than the direct shear bond stress.
Massive exploration of the natural materials for producing concretes affect to the environment condition and global warming that may cause natural disasters. Therefore the using of the concrete materials should be as efficient as possible. According to its natural behavior of the concrete material, it is strong in compression and weak in tension. Therefore the contribution of the tensile stresses of the concrete to the flexural capacity of the beams is neglected. However, removing concrete on the tension zone affects to the decreasing of flexural capacity. Based on the previous studies, beam without concrete at the tension zone using truss-system reinforcement causes the tension crack near the supports. This crack might because decreasing the flexural capacity of the beam. One of the solutions to solve this problem is by strengthening the beams using steel reinforcements. Therefore, this study aims to investigate the effect of steel reinforcement near the supports on the behavior of beam without concrete at the tension zone using truss-system reinforcement. The parameter of this study was the length of the additional reinforcement near the support. It was varied into 40D, 60D and 80D, where D is the diameter of longitudinal reinforcement. The results indicated that the tensile cracks near the support could be avoided by adding the longitudinal reinforcement. Finally, the flexural capacity of RC beams without concrete at the tension zone can be increased.
Fiber reinforced polymer (FRP) has been developed to be applied for a strengthening of the deteriorated structures. In the form of a sheet, the FRP may be applied for the strengthening of the structures by bonding it to the concrete surface. Glass composed FRP (GFRP) sheet is most commonly used due to its relatively lower cost compared to the other FRP materials. GFRP sheet is applied externally by bonding it on the concrete surface. The strengthened structures should be monitored periodically to ensure the health of the strengthened structures. Regarding the development of monitoring system of the strengthened structure, it is important to study the delamination phenomenon of the bonded GFRP. Therefore the delamination mechanism is important to be clarified. Many studies have been done to investigate the bonding characteristics of GFRP sheet under direct tensile loading. However, the studies on the bonding characteristics of GFRP sheet on the strengthened beams due to flexural loadings are still limited. A series of concrete beams strengthened with GFRP sheet on extreme tension surface were prepared. The beam specimens ware loaded under four-point bending test gradually up to the ultimate capacity. Results indicated that prior to final delamination, a local delamination occurred which was indicated by the suddenly decreasing of an applied load. The delamination of the GFRP sheet may be initiated by the flexural cracks occurred on the beams.
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