Primary Exploration On The Fatigue Property Of RC Beam Reinforced By CFRP In Salt-spray Environment

A large quantity of engineering practices indicate that application of Fiber Reinforced Polymer(FRP for short) to reinforced concrete(RC) members can improve bearing capacity and durability of structure and members obviously. In order to discuss the reinforcement effect of FRP sheet, foreign and domestic scholars have made a large quantity of researches on FRP material property, bearing capacity and durability of reinforcement member. However, there is no experimental method of member durability under the coupling of salt-spray environment and fatigue load. Therefore, with the active bridge in coastal area as research background, the paper utilizes new FRP sheet------carbon fiber laminate(CFL) invented by the research group to construct RC member reinforced with CFL and takes it as research object. With consideration of bad salt-spray environment of coastal area, the paper discusses the experimental method of reinforcing durability of RC member reinforced with CFL under the coupling of salt-spray environment and fatigue load, develops and integrates intelligent environment simulation and control system that can realize such experimental method and verifies the feasibility, stability and reliability of such system through experiment. The main content and conclusion of this paper is as follows:(1) In order to realize durability experiment of bridge structure under coupling of saltspray environment and fatigue load, with the assistance of vendor, the research group develops and integrates corresponding experiment system. There are two parts: intelligent environment simulation and control system; fatigue load system. Of them, the function and technical features of intelligent environment simulation and control system are: a) it can meet the simulation in various experimental environments such as salt-spray, wet-hot and freeze thawing, etc. b) all technical indicators cannot be lower than the current same type of product and be able to realize intelligent combination in multi-field environment conditions; c) it can meet the need of largesize bridge structure model test-piece experiment; d) it can match with the modified MTS material test system.(2) The experimental salinity set in this paper is 3%, 5% and 7% respectively and the experimental temperature is 10℃, 35℃ and 50℃. Under the cyclic loading with the maximum of 27.5kN, the paper performs durability experiment research on nine CFL reinforced RC beams under coupling of salt-spray environment and fatigue load. It verifies the feasibility, stability and reliability of such experimental system.(3) The fatigue experiment and analysis result of reinforced beam in salt-spray environment indicate that under the same salinity, with the temperature rising, the fatigue service life of reinforced beam appears descending; but at the same temperature, when the salinity is less than 5%, the fatigue service life of reinforced beam increases with the increasing of salinity; when the salinity is more than 5%, the fatigue service life of reinforced beam decreases with the increasing of salinity.(4) In order to explore the rule that fatigue service life of reinforced beam is affected by salt-spray environment, the paper proposes the semi-empirical formula of Fatigue service life N, temperature T and salinity K. Through discussing evolution rule of midspan flexibility of reinforced beam, the research result indicates that when temperature is certain, 5% salinity affects midspan flexibility~fatigue service life curve most greatly and the deterioration of fatigue property of reinforced beam is most serious.(5) Through discussing the evolution rule of dynamic secant stiffness of reinforced beam, the paper finds out in the first stage of reinforced beam fatigue, temperature affects dynamic secant stiffness of reinforced beam greatly. In the same salinity condition, linear stiffness reduces with the decrease of the temperature, vice verse. In the second stage of reinforced beam fatigue, in the same salinity condition, the higher the temperature is, the declining of reinforced beam stiffness is faster. In the third stage, when one end of CFL is stripped from concrete completely, the longitudinal reinforcement nearby main crack breaks, the stiffness of reinforcement beam declines rapidly and fatigue destroy happens.(6) The paper analyzes the evolution rule of CFL reinforced beam damage under the coupling of salt-spray environment and fatigue load with residue stiffness as parameter and sets up fatigue accumulative damage model under the experimental condition in this paper.