Experimental Research On The Flexural Behavier Of RC Beams Strengthened By Fiber Cloth Under Quadratic Loading

Making a comprehensive survey of the structure or structural member which were reinforced at present, it mainly includes following several kind of situations:1)The determination that the structure need to be reinforced by fibre cloth was made at the design stage; 2) the structure need to be reinforced by fibre cloth before the operational phase; 3) the structure were discovered that the supporting capacity is insufficient and needs to be reinforced by fibre cloth in the operational phase;4) the structure need to be reinforced by fibre cloth in the reconstructing and operational phase .Mostly the testing research in the field of FRP reinforcing the structure which need to be strengthened belongs to initial loading problem. And the research results are only suitable for the first two kind of reinforcement works. Regarding latter two kind of reinforcement,we need more researches and tests specially.In this paper,twenty RC beams reinforced by fibre cloth were tested. they include three kind of types: some beams without reinforcement,some with reinforcement before loaded and some reinforced beam under the load. The researching major effect factor include ratio of steel, quantity, type of fibre cloth, degree of the load in advance. The test result indicated that:1. The effect of the reinforcement will decrease when the ratio of steel increases; when the layer increases, effect will be greater; the greater pre-load is, the worse effect of reinforcement is.2. As far as the beams with load in advance, the greater pre-load is, the worse effect of reinforcement is. It is supposed to decrease the influence of reinforcement from the pre-load.3. The reinforcement by fibre cloth has limited the increase of beams'flexibility in the certain degree, reduces the maximum and has the width of the crack been evener;the the beams'rigidity increased for Reinforcement by fibre cloth;unloading also had influence on rigidity ; the beams'ductility decreased after reinforcement.4. The quantity of lagging strain relates directly to the incremental quantity of the supporting capacity.the bigger pre-loading degree is, the bigger lagging strain is,and the incremental quantity of thesupporting capacity would be less. unloading may effectively reduce quantity of the lagging strain.This paper also aimed at the lagging strain and carried on the special analysis; it also proposed the computational method s'lagging strain.By comparing supporting capacity s'computational value with the experimental value, we found that the computational result could tally well with the test result. The paper also brought forward a method for accounting the best unloading value.the mothed could provide a reference for this kind of reinforcement designing work.