Experimental Study And Theoretical Analysis On Flexural Behavior Of GFRP-concrete Composite Beams

GFRP profiled concrete composite beam can make full use of the characteristics of strong tensile ability of GFRP and strong compressive ability of concrete.The interface connection between GFRP and concrete and its combined form have great influence on the mechanical behavior of composite beam.This combination has the following advantages over the traditional combination:(1)It can prevent the concrete lift from GFRP I-shaped profile because of the upper flange of GFRP I-shaped profile buried in the concrete;(2)It can effectively enhance its cooperative deformation ability,because the contact area between concrete and GFRP is increasing;(3)In the case of accidental negative bending moment,due to the existence of the upper flange of the GFRP I-shaped profile,the crack development can be effectively restrained and the bearing capacity under the negative bending moment can be increased.Based on this,the flexural behavior of GFRP-concrete composite beam is studied in this paper.The results are as follows:1.In order to study the flexural behavior of GFRP-concrete composite beams,eight specimens of composite beams with different interface connections and GFRP thickness were studied.The failure mode,load-span deflection curve,load-strain curve and load-slip curve are obtained.The failure mechanism,deformation characteristics,strain variation and crack distribution are studied.The influence of interface connection and thickness of GFRP on flexural failure mechanism and bearing capacity of composite beam are analyzed.The results show that the failure patterns of the specimens include three cases: concrete crushing in the compression zone across the middle section,Compressive zone concrete crushing and GFRP upper flange breaking,GFRP bottom fiber crack.The specimens with flange bolts on the surface of the GFRP and the interface sandblasting show good synergistic ability,and the interface slippage is relatively small.The untreated specimens with open flange and untreated interface on GFRP profile have poor synergistic working ability and larger interface slip.Because of the small hole in the flange of GFRP profile,the coarse aggregate of concrete can not enter into the hole to form effective concrete tenon,and can not transfer shear force effectively.Instead,the opening reduces the stiffness and bearing capacity of the specimen.2.Based on the failure mechanism obtained from the test,three calculation methods of flexural bearing capacity are put forward,which are not considered slip,partial shear connection and interface shear resistance,and the calculated values are compared with the experimental values.The calculated value is less than the test value and has certain safety reserve,which can be used as reference for engineering design.3.Based on the failure mechanism obtained from the test,the reasonable basic assumption is introduced,and a calculation method of deflection of GFRP composite beam without or without slip is proposed.The test value is less than the calculated value and has a certain safety reserve.It can be used as a reference for engineering design.