Study On The Indirectly Stiffness And Long-Term Creep Behavior Of Beam Bridge Strengthened With Prestressed CFRP Plates

Our country has experienced the rapid development of the basic construction period since the founding of the PRC,and a great number of bridges and houses have been built.With the growth of the service life,due to improvement of standards,improper design and construction,increasing load,aging of materials,environmental corrosion,change of use function and so on,many bridges in the early days of the founding of the PRC are faced with demolition reconstructio n or reinforcement.Because the traditional reinforcement method has the shortcomings of the construction difficulty,long duration,corrosion resistance and poor durability,If the bridge demolition and reconstruction,it is bound to bring a great economi c burden to the state society.The technology of using prestressed carbon fiber reinforced concrete bridge is one of the fast developing technology in recent years.By applying prestress on carbon fiber sheet,we can make full use of the high strength of carbon fiber sheet,but also can improve interfacial bond stress distribution of carbon fiber sheet and concrete interface,and delay the destruction of carbon fiber.Because carbon fiber sheet has many advantages,such as high tensile strength,corrosi on resistance,easy to design,simple and efficient construction etc.,so in recent years,both at home and abroad,many scholars attaches great importance to the prestressed carbon fiber sheet reinforcement of reinforced concrete members,and a large numb er of research results have been achieved.But throughout the previous research achievements,there are still the following problems: long term creep behavior of prestressed carbon fiber sheet is few,which is limited to short-term strain observation;study on bending stiffness of reinforced by prestressed CFRP plate is not thorough;the specimen size is small and the size effect is larger;there is almost no research on the mechanical properties of the flexural members strengthened with prestressed carbon fiber sheet under variable bonding condition;the reinforcement technology of prestressed carbon fiber sheet is rarely applied in entity bridge engineering,especially the bigger bridge reinforcement,the main reason is that tension device and carbon plate anchorage can not meet the use requirements.According to the previous research results and deficiencies,this paper has carried on the following research work:(1)The relevant literature of the bending member strengthened by the prestressed CFRP sheet at home and abroad was investigated,the work and research status of domestic and foreign research on the strengthening technology of prestressed carbon fiber sheet was understood,the advantages and disadvantages of the existing research achievements at home and abroad were analyzed.Based on the above research,The research ideas and main research contents of this paper were presented.(2)Static load mechanical performance test of reinforced concrete flexural members strengthened with prestressed carbon f iber reinforced concrete was carried out,the influence of the strengthening technology of prestressed carbon fiber reinforced plate on the bearing capacity,crack resistance and bending stiffness of the strengthened structure was studied;The strengthenin g effect of Prestressed CFRP plate in the two times of the structure was studied,and the effect of different reinforcement ratio on the strengthening effect was analyzed;On the basis of the above laboratory tests,through theoretical analysis,the calcul ation formula of the indirect stiffness of reinforced concrete flexural members strengthened with prestressed CFRP plates was derived,finite element analysis was carried out,and the theoretical calculation results were in agreement with the experimental results,which could be used to guide the design of engineering reinforcement.(3)Under the condition of indoor standard,the long term creep performance of the prestressed CFRP plate was studied,the long term stability of the carbon fiber sheet tension anchorage system and its influence on the prestress loss were investigated;A long-term observation on the strain of carbon fiber sheet under the action of long-term prestress was carried by using fiber Bragg grating sensor on the surface of carbon plate,the long term creep performance of the prestressed CFRP plate was obtained;Based on the laboratory test,the formula of the strain of Prestressed CFRP plate under the action of long-term stress was derived by theoretical analysis,which could be used to guide the design of engineering reinforcement;The long-term creep of the carbon plate in the solid bridge reinforcement project was monitored,and verified the correctness of the formula.(4)Based on the analysis of the relationship between the stiffnes s of the beam and the frequency and the deflection of the beam,the natural frequencies of flexural members strengthened with prestressed carbon fiber reinforced plate were derived by using dynamic stiffness method,the calculated values were in agreement with the measured values,which verified the correctness of the formula;The formula for calculating the deflection of reinforced concrete beams strengthened with prestressed carbon fiber reinforced concrete was analyzed theoretically,and the calculated r esults were in good agreement with the experimental results,which could be used to guide the design of reinforced concrete beams.(5)The experimental study on the reinforced concrete flexural member with variable bonding prestressed carbon fiber reinforc ed concrete was carried out,the mechanical properties of the beams strengthened with non bonding,bonded and bonded prestressed reinforcement beams under external loads were compared and analyzed,and crack phenomena in three kinds of state were observed and comparative analysis;Theoretical analysis was made on the formation mechanism of the cracks with bonding,non bonding and variable bonding.(6)The Zhu Jin-du bridge which is located in Xiangxiang City of Hunan Province was strengthened by using stren gthening technology of prestressed carbon fiber sheet,the reinforcement design scheme,the tensioning process and the cost of the construction were introduced and analyzed;Load tests were carried out on the bridge,and the reinforcement effect was evalua ted;Fiber Bragg grating sensors were embedded on the surface of reinforced carbon fiber,the creep behavior of Prestressed CFRP Plates under long-term loading was studied by observing strain of prestressed carbon fiber sheet.