Study On Cast-in-place Floor Slab Strengthened With Cfrp Sheets

CFRP Sheets has the advantages of high strength, light weight, high fatigue resistance,chemical resistance and durability. About10times tensile strength of the second ordinarysteel, according to the classification form national standards [1], thickness of CFRP sheetscan be divided into the three levels of0.111mm,0.167mm and0.25mm. CFRPstrengthening methods does not increase the original slab’s cross section, which is widelyapplied to strengthening concrete structures nowadays.Firstly, in this paper, several commonly methods of strengthening reinforced concretestructure are introduced. To begin with, the domestic and foreign development presentsituation of CFRP strengthening concrete structure is discussed, and bearing capacitycalculating methods were stated. Besides, based on the practical example that cracksappearance on cast-in-place floor slab in a building material market, though analysis onfield measurement and theoretical calculation, we judged the reason of these slabs’ cracksappearance. Followed, we find out that these appearance cracks had influenced slab’snormal using function. In addition, combining with the real situation, we make a compositeanalysis with these cracking causes and a design that CFRP sheets were pasted on slabsscattering just like "#" shape. Moreover, taking the third floor ((4-1/4)/(A-B) axis)strengthened by CFRP sheets of C1building as the research object, the values of flexuralrigidity and mid-span deflection are calculated and checked. We can draw to conclusionthat using CFRP sheets have a good effect to reinforce concrete slab, which can strengthenslab’s rigidity、increase slab’s flexural rigidity and reduce slab’s deflection.Secondly, based on this strengthen slab (third floor ((4-1/4) cross (A-B) axis) of C1building), finite element model is established by finite element software ANSYS. Firstly,this slab’s mid-span deflection, steel stress, CFRP sheets’ stress, surface concrete strain andultimate bearing capacity are discussed. Besides, many influencing factors of CFRPreinforcement effect are analyzed in this article, such as CFRP strengthening modes, CFRPthickness, CFRP amount, steel reinforcement ratio, CFRP elastic modulus and per-loaddegree. In addition, with different CFRP prestress level, reinforcement effects of this slabstrengthened with CFRP sheets are studied.Furthermore, through the above research and analysis, We draw the conclusions asfollows: As the slab is strengthened with CFRP sheets, its flexural capacity can besignificantly improved and deflection be reduced; Scattering CFRP sheets on the slab justlike "#" shape is helpful to improving its reinforcement effect and increasing its utilization; Nevertheless, If CFRP sheets’ thickness is too thick, the effectiveness of improving slab’sflexural capacity is weak; To some extend, the lower steel reinforcement ratio, the bettereffect of the slab strengthened with CFRP sheets has; To some extend, increasing CFRP’selastic modulus help to improve flexural capacity of reinforcement slab, but too largeelastic modulus go against giving full play to CFRP’s tensile strength; The effectiveness ofslab strengthened with prestressed CFRP sheets is better than non-prestressed CFRP;Applying prestress within a reasonable range, the greater level pre-stressed, the bettereffect of the slab strengthened with CFRP sheets has; The above conclusions can givereference for structural reinforcement and construction.