Experimental and Numerical Investigations on Near Surface Mounted Basalt Fibre Reinforced Polymer Bars for Flexural Strengthening of RC Beams

Abstract

One of the strengthening techniques based on the usage of FRP (Fibre Reinforced Polymer) bar is near surface mounted (NSM). It is one of the emerging techniques for strengthening structural element de cient in exural strength due to their higher strength to weight ratio, corrosion resistance and ease of application on structural el- ements. Limited studies are reported to date on the use of NSM-BFRP (Basalt Fibre Reinforced Polymer) reinforcement for strengthening of R.C. elements in literature. In the present study the performance of R.C.beams strengthened with NSM BFRP bar is presented. The e cacy of NSM-BFRP bar used as a strengthening material for beam is studied in terms of load carrying capacity, crack patterns, mode of failure, ductility ratios and strain behavior in di erent materials. The aim of this investigation is to carry out direct pull out test of BFRP bar and to know the bond slip relation and bond strength of BFRP bars. As FRP bars hav- ing certain advantages compared to steel, but the main concern is the bond behavior between FRP bar and concrete that corresponds to stress transfer from concrete into FRP bar. The pull out test is performed on C-block concrete specimen by varying di erent parameters such as groove size, diameter of BFRP bar and bonded length. This specimen o ers advantages of direct pullout type of test specimen such as man- ageable size, possibility to conduct test in slip control mode, measurement of both loaded and free end slip and visual access to test zone. The BFRP bar of 6mm and 10mm diameter was used and it was installed in groove along the surface of C-shaped concrete block of size 300 300 300 mm. Crack is observed at the face of the epoxy layer and cracks get propagated up to the free end of BFRP bar. The failure at epoxy and concrete interface is observed. The analytical model is developed and its results is compared with the experimental data. The present study deals with the structural performance of simply supported R.C. beams strengthened by using NSM technique. Flexure strengthening of R.C. beams was conducted by using BFRP bar of 6mm and 10mm diameter bar. After casting of beams strengthening technique was applied and the beam was tested as fully undam- age beam in order to identify the full load carrying capacity of beams and to know sharing of load between main steel and BFRP bar. Size of the beam was kept 100mm x 200mm x 1500mm and it was designed using I.S. provisions. Variables considered in

exure strengthening of beams are diameter of BFRP bar (6mm and 10mm), groove size (12mm, 15mm and 20mm) and numbers of BFRP bar used at tension face. The beams were subjected to four point bending load test and the rate of loading was kept 1mm/min for all beams (control beams as well as NSM strengthened beams). The ultimate load increased by 55.92%, 60.0%, 67.98% and 81.05% for 12mm NSM (6mm dia), 15mm NSM (10mm dia), 20mm NSM (10mm dia) and 2-12mm NSM (6mm dia) respectively as compared to control beam. The de ection and energy ductility index was computed and it was found that the ductility ratios of all the strengthened beams were less than that of control beam. The overall reduction in ductility of NSM strengthened beams is most likely due to the increased reinforcement on tension side. Mathematical modeling is carried out by developing numerical models for R.C. beams strengthened with NSM (Near surface mounted) technique using finite ele- ment software. All materials were modeled properly in order to simulate the actual behavior. A good agreement between numerical and experimental results is observed.