Research On Cooperative Working Behavior Of Concrete Beams Strengthened With Prestressed CFRP Laminate

Because of CFRP materials are lightweight, high-strength, corrosion resistance,etc, it has been more widely used in domestic and foreign structural reinforcementproject. In the area of reinforcement concrete structure, many countries made a seriesof FRP technical regulations, used to guide the reinforcement design in practicalengineering. In China, After referenced to the latest achievements both at home andabroad, As CECS146:2003、 JTG/T J22-2008and GB50608-2010,etc,Thesespecifications make the design more standardized.However, with the further research, these specifications exist many obviousdeficiencies. Such as, Plane-section assumption is a basic premise to calculate thebearing capacity of the bridge structure; but the above specification just simply restrict"When the structure reaches the ultimate bearing capacity of normal section, nopeeling occurred between FRP and concrete". Because there is no reliable anchorage,CFRP is easy to accorded early debonding damage, once peeled off, the premise of“Plane-section assumption” no longer applies, and caused great waste of materialstrength. And, when FRP sheet peeling, the structure often did not reach the limit stateof bearing capacity, once peeled off, the premise of “Plane-section assumption” nolonger applies. For ordinary paste FRP laminate reinforcement, when peeling occurred,the actual tensile strain is very lower. Many experimental studies show that the actualtensile strain of less than20%of its limits. Therefore, when the strain is small, theabove specifications for FRP sheet are applied, while for others it may not beappropriate.With the development of prestressed FRP technology, especially as the advancesof FRP sheet anchor technology, FRP can be issued to its ultimate strength in reliableanchoring conditions, in the larger stress level (including the initial prestress), undersuch conditions, whether it meet the plane-section assumption is still a difficult subjectwhich need lots of experiment to confirm.During bridge design which used prestressed CFRP reinforced, calculationwhether the sectional satisfies “plane assumption” is a very important precondition and,research on cooperative working behavior of CFRP board seems very important. Inorder to study under the conditions of a reliable anchorage, in this subject, mainlystudied in different levels of prestressing, different layers of CFRP laminate reinforced concrete structures, through load testing, tested the collaborative working behaviorbetween CFRP and the original components, the main results are as follows:①In the higher initial prestress levels (1400~2100MPa), The obvious CFRP platepeeling or slip were not observed in the whole test process, even the elements occurredlarge deformation, Even before the CFRP laminate reached its limit strength (before itbreak), macroscopic CFRP peeling also didn’t observed. From the perspective of test,it confirmed that the prestressed CFRP laminate can be efficiently work with theoriginal structure which under reliable anchorage measures.②In the condition of double-prestressed CFRP laminate reinforcement, not onlyno slip occurred between two CFRP plate, and between the CFRP and concrete did notobserved significant peeling or slip, it show that the double-prestressed CFRP boardalso can be work together with the original structure very good.③By comparing the strain increment between reinforced and CFRP laminate,before cracking, both increase fully synchronized; before bar yield, the difference ofstrain increment between theory and test basically agree. Considering the measurementerror and no peeling occurs, it can be inferred that CFRP laminate can work with theoriginal structure; thus indicating the CFRP laminate can also work well with theoriginal structure in the whole process,it also meet Plane-section assumption.The above studies shows, under a reliable anchorage condition, the prestressedCFRP plate and original structure formed a surface bonded prestressed system, ensuredthe CFRP laminate did not strip from the concert, and work together with the originalstructure in the whole process, it basically meet the plane-section assumption, thisresults has a very important reference value in calculate carrying capacity which useprestressed CFRP laminate reinforced.