DOI: 10.14457/tu.the.2015.161
title: Strengthening of RC Members using Natural Fiber Composites

description: This thesis is aimed to investigate the strengthening of reinforced concrete (RC) members by using externally bonded natural fiber reinforced polymers (FRP) composites. Natural FRP composites were applied to the RC members by hand lay-up method. The behavior and  failure mode of strengthened specimens were experimentally investigated. The experimental program in this study was divided into four main parts. The first part discusses the compressive behavior of small scaled concrete columns confined with sisal FRP composites jackets.Sisal fiber thickness, type of resin and concrete strength were considered as parameters. A total of 45 plain concrte cloumns were cast and tested under axial compression up to their failure. The experimental results show the efficiency of using sisal FRP composites jackets to increase load carrying capacity and ductility of concrete columns compared with the un-strengthened specimens. The comparisons between control and strengthened specimens were made and discussed in Chapter 4. The enhancement of ultimate load becomes more significant as the sisal FRP thickness was increased. The efficiency of low strength concrete with sisal FRP composites jackets is found greater than high strength concrete.  The second part presents the experiemental study conducted on the strengthening of concrete beams using sisal fiber reinforced polymer (FRP) composites. The parameters in this study were sisal fiber thickness, resin matrix (epoxy and polyester resin) and concrete strength.  Six control beams and twenty four  sisal FRP strengthened beams were subjected to three-point bending loads, loaded statically to ultimate failure. The results showed that Sisal FRPs are very effective to enhance the ultimate load carrying capacity and deflection of the strengthened beams compared with un-strengthened beams. The behavior and failure mode of all specimens in this group were discussed in Chapter 5. There is found an  increase in ultimate load as the Sisal FRP thickness was increased for different types of concrete strengths. Both resin matrices are found effective to bond sisal FRP with concrete, however epoxy resin is found better than un-saturated polyester resin. Based on experimental results, it can be concluded that sisal FRP has a potential to increase load carrying capacity of strengthened beams.  The third part shows the series of seven reinforced concrete (RC) beams which were strengthened using externally bonded sisal FRP composites with different types of resin. All specimens were subjected to one point loading and tested up to failure. Epoxy resin and un-saturated polyester reisn were used as the adhesive to bond the concrete with Sisal FRP composites. The effects of externally bonded sisal FRP  technique on the reinforced concrete (RC) beams of diffierent resin matrices and end-anchorage system were experimentally observed. The sisal FRP composites were attached at the bottom of the strengthened reinforced concrete (RC) beams . The experimental results showed that sisal FRP thickness has remarkable influences on the strengthening efficiency of externally-bonded FRP for enchancing the ultimate load of reinforced concrete (RC)  beams. The behavior and failure mode of all tested beam specimens were presented and discussed in Chapter 6. The proposed epoxy anchors with steel plates is found to be significant to prevent the de-bonding of sisal FRP from concrete.The fourth parts describes the efficiency of epoxy-bonded hemp fiber reinforced polymer (FRP) composites in flexural strengthening of reinforced concrete (RC) beams. A total of sixteen reinforced concrete (RC) beams were cast and tested under two-point loading up to failure. The test parameters included fiber thickness, strengthening configuration, anchorage system and internal reinforcement ratio. The experimental results show the capability of hemp FRP composites to increase the loading capacity in flexure of RC beams compared with the un-strengthened beam. The enhancement of ultimate load becomes more significant as the hemp fiber thickness is increased. The effectiveness of strengthened beams in U-wrapped scheme is found greater than strengthened beams in bottom-only scheme. The propsed epoxy anchors with steel plates and hemp anchor (U-end anchor) are found to be effective to prevent the de-bonding of hemp FRP from concrete and to restore ductility of the strengthened reinforced concrete (RC) beams. The maximum increase in ultimate load of low internal reinforcement ratio group was up to 189%. Whereas the highest increase in loading capacity of high internal reinforcement ratio group was only 44.5%. Comparison in ultimate load and failure mode of all tested beam specimens were carefully investigated and discussed in Chapter 7.  Chapter 8 presents the finite element analysis carried out on reinforced concrete (RC)  beams strengthened in flexure using hemp FRP composites. VecTor2 is a nonlinear finite element (FE) software which has been developed at the University of Toronto. FE program VecTor2 was used to model and analyze the reinforced concrete (RC) beams strengthened by using externally bonded hemp FRP composites. It is found  that the results obtained from the VecTor2 were quite similar with the results from experiment. The finite element models has capability to predict the behavior of reinforced concrete (RC) beams especially strengthened beams using externally bonded FRP technique. This finite element program is not only effective to predict cracks at every step of loading, but also failure mode of reinforced concrete (RC) beams.