Research On Flexural Performance Of Reinforced Concrete Beams Strengthened By Combined Methods

At present, because of aging or change in use, many concrete structures can’t meet the demand of strength, stiffness, stability and durability. So they need to be repaired, reinforced or rebuilt. As a result, the research on strengthening and retrofitting structures are being more and more important in the world. At home and abroad, there are a lot of researches about reinforcing concrete structures. The section enlargement method, strengthening with prestressed high strength steel wire, stick steel strengthening method, strengthening by adding support points are all traditional methods. These methods have both advantages and disadvantages.Carbon Fiber Reinforced Polymer composites are new materials, which have high strength, low density and corrosion resistance. Now in the field of reinforcing concrete structures, as a new substitute of steel, they are widely applied in the world. Externally bonded and near-surface mounted CFRP are commonly used in strengthening structures. However, because of different factors about today’s technology or craft, reinforcing with CFRP sheets or CFRP bars alone can’t meet the requirement of strengthening concrete beams. So, in academia it is more and more important about how to reinforce with combined methods. In order to solve the problem of the insufficiency of reinforcing with a single method, on the basis of the single method, this dissertation does research as follows:(1) On the basis of the method about reinforcing with CFRP sheets, CFRP bars or prestressed high strength steel wire ropes, we come up with the construction craft to reinforce with CFRP sheets and CFRP bars, with CFRP sheets and prestressed high strength steel wire ropes, with CFRP bars and prestressed high strength steel wire ropes or with CFRP sheets, CFRP bars and prestressed high strength steel wire ropes.(2) We do research on 6 reinforced concrete beams strengthened by combined methods and the flexural performance is researched via experiments, then we analyze the failure mechanism and the failure characteristics of every test beam reinforced by combined methods. Besides, we confirm that the plane section assumption is still right for every test beam that is strengthened by combined methods, and compare the ultimate load of every reinforced beam with that of the standard beam and confirm that this combination meets the requirement and the cracking load and the yield load increase, the ductility decreases, and the crack development is constrained effectively. Moreover, according to the comparison between the concrete beams without prestress and other beams, we confirm that because of the prestress the crack development is constrained effectively and the cracking load increases.In addition, according to the results of the research about the test beams that are strengthened differently, we confirm that if the amount of added reinforced materials increases, then the ultimate load will increase.(3) According to the results of our experiments, on the basis of the design of concrete structures and reinforcing with a single method, we can put forward the formula for calculating the flexural strength of every concrete beam reinforced by combined methods, then compare the theoretical value with the experimental value and then confirm that the calculation method is correct.