Nonlinear Analysis of Reinforced Concrete Beams Strengthened with Prestressed CFRP sheets Under Cyclic Load
DIYALA JOURNAL OF ENGINEERING SCIENCES,
Volume 5, Issue 1, Pages 117-137
AbstractABSTRACT:- Analysis of reinforced concrete beams strengthened by prestressed CFRP sheets has been investigated in this paper. A three dimensional finite element analysis ANSYS computer program (version 9.0) was conducted to obtain the response of the strengthened beams. The eight –node brick elements(solid 65) are used for the idealization of concrete while the CFRP sheets are idealized by using three-dimensional layered elements (solid 46).The steel plates are idealized by using three dimensional solid elements (solid 45).Five beams are analyzed in study ,four with prestressed –CFRP sheets and one with nonprestressed- CFRP sheet. The effect of different level of prestress ,induced by prestressing the CFRP –sheets, on the cracking loads and flexural stiffness of the strengthened beams are studied. It is found that the cracking load and the flexural stiffness are significantly increased as the level of prestress increased. The response of the strengthened beam under cyclic loads is also conducted in terms of deflection versus number of cycles which is related to the cyclic
behaviour of the constituent materials used in the beam ( concrete , tension steel, and CFRP sheets).
The deformation of each these materials under cyclic loadings is presented in terms of measured strains as a percent of the number of cycles of fatigue. The results obtained from finite element analysis are compared with available experimental results and the comparison gives good accuracy.
Keywords: Prestress ,CFRP, strengthened, cracking loads, flexural stiffness ,cyclic loads.
The strengthening of reinforced concrete beam by means of externally bonded fiberreinforced
plastic (FRP) sheets has gained great attention in recent years because the
strengthening technique by using(FRP) sheets presents several practical advantages due to an
easy installation on site, great geometrical flexibility, high strength-to-weight ratio, good
durability, fatigue resistance and low creep (Hollaway and Leeming 1999) . Although
bonding a FRP sheet to a beam can increase its ultimate strength, the sheet does not
significantly change the cracking load or the behaviour of the beam under service load.
However, by prestressing the sheet, the laminate is used more efficiently since it contributes
to the load – bearing capacity under both service and ultimate conditions. Several studies
were made to investigate the behaviour of the strengthening beam by externally bonded FRP
with or without prestressing. Triantafillou and Deskovic (1991) [2 ]reported an analysis of the
problem of providing the maximum achievable prestress level without experiencing a debonding
failure in the end zone. Triantafillou et al. (1992) [3 ] verified their analytical model
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