Investigation On Temperature Effect On The Interfacial Properties Of CFRP Strengthened Steel Beams

Lots of steel bridges need to be strengthened or repaired due to fatigue damage around the world.The strenthening technique with exterally bonded CFRP(carbon fiber reinforced polymer)plate possess many advantages,such as easy installation,no increased loading and without introduced residual stress.In order to ensure the safe and lasting service of reinforced concrete beam system with external CFRP sheet,it is necessary to study the stress characteristics and failure mode of reinforced steel beam system.The failure of the steel pipe strengthened with external adhesive CFRP board mainly occurs in the interface of CFRP plate and steel structure.The failure mainly includes the following four modes: 1)Adhesion of adhesive to steel structure;2)Adhesion failure of adhesive;3)CFRP plate interface debonding;4)mixed failure mode.The temperature will affect the mechanical properties of the adhesive,thus affecting the interface strength of CFRP-steel beam and reduce the bearing capacity of steel girder.However,the huge difference of the thermal expansion coefficient between steel and CFRP may bring in shear stress in the interphase,under the temperature effect due to season change or sun irridation(alternating temperatues and temperature difference).This will lead to cumulative fatigue damage.So the adhesive and temperature are the factors that affect the interface strength of CFRP-steel beams.In this paper,the two factors were systematically studied,the main work and research results are as follows:(1)The preparation and characterization of T1 and Tc structural adhesive samples were carried out.The mechanical properties and thermal properties of the adhesive were tested.The basic data of the adhesive were obtained.(2)Reinforcement of the girder with notched steel has been carried out,and the bending strength test of the unbounded beam,T1 rubber reinforced beam and Tc rubber reinforced beam is completed,which shows that the interface strength of Tc glue is higher.Low elastic modulus adhesive due to better ductility,adhesive and CFRP sheet adhesion performance,and thus higher ultimate bearing capacity(3)The bending load test of reinforced steel beams under different temperature effects is completed.The influence of temperature on the law o f interfacial strength is studied,and the variation of the performance of different adhesives under temperature is studied.It is concluded that the temperature below the glass transition temperature is favorable for the reinforcement of the steel beam,a nd the reinforcement effect is basically lost above the glass transition temperature,and the mechanical parameters are reduced after the temperature change.