Finite Element Analysis On The Effect Of Anchorages For FRP Shear Strengthened Concrete Beams

FRP material has been widely used in civil engineering field.Reinforcement of concrete beams in engineering applications is mainly divided into flexural reinforcement and shear reinforcement.The forms of shear reinforcement can be divided into three types: side sticking,U-shaped sticking and closed sticking.The main cause of failure of reinforced concrete beams is interfacial peeling between fiber cloth and concrete caused by shear cracks and bending cracks.Now the common method used in engineering is to stick FRP-U hoop at the end of FRP or along the whole beam to prevent the stripping of FRP cloth from the interface of concrete.In this paper,the finite element analysis of FRP shear strengthened concrete beams and anchorage effect will be carried out.The research contents and main conclusions are as follows.1.The finite element analysis of shear strengthening effect of experimental beams based on the Concrete Damage Plasticity is carried out.We will establishment the finite element models of strip reinforcement,U-type reinforcement and full-encapsulated anchorage in literatures.The rationality of the numerical model and the constitutive relationship of concrete is verified by comparison of load-displacement curves between experiment and numerical simulation.Based on a reasonable finite element model,numerical analysis of 18 finite element models with spacing of 25 mm,50 mm and 100 mm and width of U25,U50 and U75 for three reinforcement methods was studied.The results show that the optimum reinforcement form,width and spacing of FRP shear reinforcement are obtained,which can provide reference for practical engineering design.2.Based on extended finite element method(XFEM)and interfacial bond stress(CZM)analysis method,the effect of FRP sticking direction on shear strengthening of concrete beams is studied.The extended finite element models of reinforced concrete beams strengthened with vertical FRP bars and oblique 45 degrees FRP bars are established respectively.The load-displacement curves of beams strengthened with vertical FRP strips are compared with the experimental results to verify the reliability of the extended finite element model.Based on the numerical results of the finite element method,the interface stress and the stress change of FRP cloth when shear inclined crack passes through FRP cloth under two kinds of reinforcement methods are carried out respectively.we will compare the crack height,interface element stress and FRP stress of the two reinforcement methods under the same external load.And the result is oblique 45° bonding reinforcement is better than vertical bonding reinforcement in anchorage effect.3.Based on the calculation method of Chapter 3,the anchorage effect of reinforced concrete beams strengthened by FRP with U-shaped anchorage at the end and the whole beam is analyzed.We will establish finite element models of bending cracks,shear cracks and bending-shear cracks.The reinforcement effect,crack height,interface stress and BFRP distribution stress under different load levels of reinforced concrete beams strengthened with BFRP under two U-type anchorage modes are compared.The results show that the two types of anchorage have little difference in improving the bearing capacity of reinforced beams and restraining the crack propagation of concrete.However,when the end of BFRP sheet is anchored,the distribution of interface stress and BFRP sheet stress is more uniform and peeling failure is prone to occur near cracks.In the case of full beam anchorage,the interface stress decreases and the interface peeling is not easy to occur.The stress of BFRP cloth between U-type anchorage is larger and the beam is prone to fracture of BFRP material.4.The design method of FRP shear strengthening commonly used in engineering is studied.Based on the calculation formulas of national codes,this paper studies the bearing capacity calculation of shear-strengthened concrete beams in American codes and Chinese codes.The experimental result are compared with the design results based on the code.The results show that the calculation results in the code are conservative.Combining with the results of comparative analysis,some suggestions are put forward for the shear strengthening design of reinforced concrete beams.