Experimental Study On Size Effect Of Small Shear Span Ratio RC Beams Shear Strengthened With FRP Wraps

Fiber Reinforced Polymer (FRP) has been increasingly used in strengthening existing reinforced concrete structures and other structures due to its advantages such as corrosion resistance, high strength and light weight. FRP is particularly suitable for shear strengthening due to the wide variety of strenthening configuartions of FRP. However, the majority of the current research on the FRP shear-strengthened beams is carried out for small size specimens; as a result, the strength models in existing FRP guidelines had been substatianted against test database of small size specimens. However, the specimens needing strengthening in practicce are ussually much larger than the test specimens.As a result, due to the size effect of shear strength for RC beams, the direct application of the existing shear strength models in the shear strengthening of RC beams in practice may overestimate the shear contribution of FRP, leading to unsafe results. Based on the above research background, this thesis presents an experimental study on the size effect of small-shear-span-ratio RC beams shear strengthened with FRP wraps; a total of 12 rectangular beams were tested with the main parameters invesitgated being beam height (i.e.300mm、600mm and 900mm) and effect of steel stirrups (with and without stirrups). Based the experimental results from this study, some important issues can be preliminarily clarified, including the shear strenghtening effect of FRP wraps on large size RC beams with and without steel stirrups, shear interction among different part of the strengthened beams, and the size effect of the RC beam shear-strengthenend with FRP wraps.. The research contents in this paper mainly include following three parts:1) Comparative study on the shear strengthening effect of FRP wraps on RC beams with and without stirrups. The load-displacement reponses as well as the measured strain development in stirrups and FRP strips showed that the FRP wraps has bettern shear strengtening effect and ductility for RC beams without stirrups than for RC beams with stirrups. The test results also showed that although the FRP wraps can enhance the ductility of RC beams with stirrups, their shear strenghening effect of FRP wraps is very slight probably due to the change of failure mode (to shear diagonal compression failure) of the strengthened RC beams.2) The shear interaction between concrete and FRP. Based on the measured FRP strain values, the shear contribution of FRP can be separated from that of concrete (or reinforced concrete) and the latter can be further compared with those of the correspdonging control beams. It can be obtained from the above analvses that shear interaction exists betweenFRP and concrete, and the existence of FRP delays the decline ofshear contribution of concrete. The effect becomes more apparent with the increasing of beams size. Therefore, direct use of the simple superpostion principle (V=Vf+Vc+Vs) may lead to overestimating the shear contribution of the FRP-strengthened concrete beams.3) Size effect of the RC beams (with and without stirrups) shear strengthened with FRP wraps. The test results showed that for RC beam without steel stirrup, the shear strengthening decreases size effect of the nominal shear strength; samilar conclusion can be drawn for the RC beam mainly because the failure mode of the strengthened has been changed to diagonal compression failure.