Experimental Study On Partial Degenerated Strength Reinforced Concrete Columns Wrapped With CFRP

Fiber reinforced polymer or plastics has been widely used as a new material for strengthening existing civil infrastructures because of its superior properties in high tensile strength, light weight, ease for construction, no addition to dimensions of members, etc. especially in the aspects of upgrading columns and piers. There have been a number of studies on the uses of this technique, but theoretic researches of that still drop behind its applications in construction and need being further perfected. However, most of the researches conducted so far all focus on the same strength. Actually, partial of the construction or constructional member might be degenerated because of less control of construction or environmental corrosion. In this case, if entirely strengthened will inevitably cause a waste. In order to simulate this situation, through the related researches about FRP confined concrete columns in the world and based on the experimental study, this paper analyzes the mechanical performances of partial degenerated strength reinforced concrete square columns wrapped by CFRP compressed under axially, eccentrically loading. The main contents and achievements of this paper are summarized as following:In this thesis, 5 partial degenerated strength RC columns confined with CFRP were tested under axial compression. Based on the destructive tests, this paper analyzed strengthening effect with different CFRP layers. The results show that: because CFRP effectively bond the concrete' lateral deformation, the ultimate compressive strength and deformation capacity of concrete have been prominently enhanced, the plastic distortion capability of steel bar can be made full use of and has the positive attributes of improving the carrying capacity and ductility of structure. Meanwhile, The experimental results indicate that the ultimate bearing capacity and ductility of the column increase when strengthened with transverse CFRP, but the increasing degree of bearing capacity reduces while CFRP layers increases, which means for a certain reinforce mode better reinforced rate exists. At last, a practical calculating formula of the ultimate compressive strength of the reinforced concrete columns wrapped with CFRP under axial loads is proposed based on this test and according to the existed model. Through comparing the calculated results to the test results, it shows reasonable agreement with test results. In this thesis, 12 partial degenerated strength RC columns confined with CFRP were tested under eccentric compression. Based on the destructive tests, this paper analyzed the strengthening effect with the parameters such as different CFRP amount, different strengthening mode and different eccentricity. The experimental results indicate that the ultimate bearing capacity and ductility of the specimen have a certain increase when strengthened with transverse CFRP, but it is not in linear relationship, that is to say, the increasing degree of bearing capacity reduces while CFRP layers increases; the results also show that CFRP can enhance the strength and ductility of columns with small eccentricity effectively, but the enhancement of capacity is very small and ductility is still high for columns with critical eccentricity; the distribution of sectional strain accords with plain section assumption; the tensile strain of external FRP exists distinct strain gradient due to uneven dilation of compressed concrete, and the testing value of axial magnifying coefficient of eccentricity is far different from the calculating value according to concrete code, and so on.