Seismic Performance Of Elliptical FRP Tube Confined Reinforced Coupling Beams

Shear wall structures usually exist in the form of coupled shear walls.Coupled beams,as the horizontal members of the structure,play an important role in coupled shear wall structures,and are considered to be the first seismic defense line and the main energy dissipating member of the structure.However,it has been proved that the shear strength and ductility of traditional RC coupling beams are insufficient.In order to improve the mechanical performance of coupling beams,Professor J.G.Teng from Hong Kong Polytechnic University proposed a new type of coupling beam,i.e.FRP confined reinforced concrete beam.The fibers of the FRP tube are mainly arranged along the hoop direction,which can effectively enhance the shear capacity of the beam.At the same time,the FRP tube can prevent the concrete spalling in the compression zone and improve the strength and stiffness of the coupling beam after yielding.As a part of the research on the mechanical properties of FRP tube confined reinforced concrete beams,the main contents of this paper are as follows:(1)the shear performance of coupling beam is an important guarantee of its seismic performance.In this paper,two FRP confined reinforced concrete coupling beams with shear span ratios of 1 and 0.8 and cross-section shapes of circular and ellipse are tested.The bending failure of the two specimens finally occurs.It shows that the shear strength of FRP tube is very significant,and the shear failure of FRP confined reinforced concrete coupling beams is not easy to occur.(2)The cyclic horizontal loading tests of five FRP confined reinforced concrete coupling beams have been completed.The main conclusions are as follows: when the anchorage length of the composite beams into the wall limbs is small,plus the shear resistance of the coupling beams are enhanced by the FRP tubes,the shear sliding failure of the concrete interface may occur;Under the same conditions,the larger the span to depth ratio,the larger the FRP tube thickness and the smaller ratio of major to minor axis,the plumper the hysteretic curve,and can consume more seismic energy.The stiffness of specimens with shear sliding failure tends to be reduced promptly.Specimens with the larger span to depth ratio have a faster stiffness degradation rate.(3)According to the test,the finite element analysis software was used to establish five specimens of FRP confined reinforced concrete coupling beams,and monotonic loading was carried out on the models to obtain the theoretical loaddisplacement curve,which was compared with the skeleton curve obtained from the test.The comparison outcomes indicate that the theoretical curvatures almost coincide with the experimental curvatures in the elastic stage.Nevertheless,the stiffness degradation of the experimental curvature is often quicker than that of the FE calculation.