Experimental Investigations of RC Deep Beams Strengthened in Shear using NSM CFRP System

Abstract

This paper presents the test results of an experimental study that investigates the behavior of RC deep beams strengthened in shear with externally bonded (EB) and near surface mounted (NSM) techniques using CFRP strip. A total of 6 RC deep beams were constructed and tested under four-point bending. Test specimen had a cross section of 150 × 500 mm and a total length of 1450 mm. This study included two parameters; techniques (NSM and EB) used for strengthening and amount of shear steel reinforcement ratio. All of the strengthened beams have the same CFRP configurations; and CFRP strips were bonded perpendicular to the diagonal connecting the loading and the support points. The specimens were divided into two groups based on the shear steel reinforcement ratio. There were three beams in each group. One of them was a control beam, the rest of the beams in each group were strengthened by EB or NSM techniques. The amount of CFRP strip in EB and NSM techniques is equal. All of the beams were loaded until failure and during the experiment, deflection and compressive strains of concrete, tensile strain of longitudinal steel bar at mid span and crack width of flexural and shear, were measured. The test results showed that shear strengthening of the deep RC beams with NSM technique causes to increase in ultimate load capacity and ultimate deflection capacity by 18% and 16% respectively, compared with the control beam. Also, the ultimate load capacity and ultimate deflection capacity of deep RC beams strengthened with NSM technique are 6% and 15% more than beams strengthened with NSM technique respectively. The concrete compressive strain at ultimate load of deep RC beams strengthened with NSM technique is 50% more than beams strengthened with NSM technique.

Keywords

• rc deep beam
• shear strengthening
• cfrp
• eb
• nsm