Flexural Strengthening Of RC Beams With Prestressed And Unprestressed Fabric-reinforced Cementitious Plates

Fabric-reinforced cementitious(FRC)plate is a high-powered composite plate made by fabric meshes or grids embedded into an inorganic stabilized cementitious matrix.Composite plate due to its favourable propertites,such as high strength-to-weight ratio,corrosion resistance and flexibility can be used for flexural strengthening of concrete structure.Compared to the traditional CFRP strengthening method,FRC plate was bonded to the external surface of strengthened structure with an inorganic cementitious binder.It also overcomes problems caused by organic resin binders such as poor fire-resistant performance and poor durability.The flexural performance of RC beams strengthened with fabric-reinforced cementitious plates in the tension zone was investigated.The effect of the fabric layers and prestress value of fabric on the working mechanism of strengthened beams was studied.One contrast case and four strengthening cases were designed to investigate the flexural performance of RC beams strengthened with composite plates.The load,deflection,midspan strain,fabric strain and crack development were simultaneously recorded during the tests.By numerical simulation,mechanical properties of beams in 5 cases was analysed in detail.Present study obtains the following research contents:(1)Compared with the contrast beams,increasing the carbon fabric layers increases flexural capacity from 11%to 41%.The stiffness of the strengthened beams is larger,but structural ductility decreases to a certain extent.The failure modes of the strengthened beams are related to the fabric layers(fabric reinforcement ratio).Strengthened beams with low fabric reinforcement ratio fails by FRC plate rupture in the strengthening zone.For the beams with high fabric reinforcement ratio,neutral axis moves up slowly until failure.Especially after the yielding of longitudinal steels,composite plate in tension zone could continue to bear the subsequent increasing load until the crushing of concrete in the compression zone.(2)The application of prestress on the FRC composite plates effectively improves the cracking,yielding and ultimate loads of strengthened beams.Comparison of the beams with low fabric reinforcement ratio shows that prestress exerts little influence on increasing flexural capacity.but it increases the cracking and yielding load a lot.For the beams with high fabric reinforcement ratio,the properties of the carbon fabric are fully developed.Prestress exerts remarkable influence on increasing flexural capacity.(3)Strain analysis of the beams with the composite plate shows that before the yielding load of steel,a linear strain distribution exists along the depth of the beam the strain values of the concrete,steel,carbon fabric are proportional to the applied load.A significant increase in fabric strain is observed after the yielding load.Fabric nets plays an important role in bearing the subsequent load in tension zone.(4)Based on the experimental research,a well-established analytical formula to calculate the flexural capacity and deflections of the strengthened beams is proposed.The analytical results agree with experimental results.(5)Nonlinear finite element analysis of strengthened beam in all cases is conducted by MSC.Marc software.The failure modes and the working mechanism of FRC plate strengthening are analysed.