Abstract
Carbon fiber jacketing is an efficient technique for increasing the strength and strain capacity of concrete circular and square section columns subjected to axial load, although confinement efficiency decreases for rectangular cross-section members. The research project BIA 2016-80310-P includes an experimental program on intermediate-size plain concrete specimens strengthened with carbon fiber jackets, mostly with square and rectangular cross-sections. The results, alongside others with similar characteristics from two databases published, are compared to predictions of four international guides. The incidence of the key parameters in the experimental results is analyzed, such as the aspect ratio of the section, the effective strain in FRP jacket attained at failure or the rounded corner radius. As a result, two efficiency strain factors are proposed, one for circular and another for rectangular specimens. The predictions contained in certain guides, based on a simple linear design-model, are improved by using the proposed efficiency strain factor for rectangular sections.
Highlights
RESUMEN: Análisis experimental y modelos de resistencia adoptados por distintas guías internacionales para pilares de hormigón confinados con Fiber reinforced polymers (FRPs) sometidos a compresión centrada
They are usually based on approaches devised for circular columns, which are modified by reduction factors related to the two key parameters: the effect of confinement in non-circular sections and the effective strain in the FRP jacket
The results have been compared to others from carbon-fiber reinforced polymer (CFRP) strengthened plain concrete specimens with square and rectangular sections that are included in the database compiled by Pham and Hadi (7)
Summary
The improvement of concrete strength in the retrofitted column depends on the confinement that the FRP jacket can attain. The confinement is more efficient in circular cross-section members, where the FRP confining pressure (fl) can be considered uniform over the entire perimeter (Figure 1). The confining pressure can be expressed as a function of the modulus of elasticity (Ef), total thickness (t) and tensile strain of the FRP jacket, as well as the diameter (D) of the concrete column. The FRP confinement is non-uniform and is most concentrated at the corners. The FRP effective strain is lower than the strain achieved in circular columns. It should be noted that the confined concrete stress over a rectangular section is uneven due to the non-uniformity of the FRP confinement. Strength is commonly accepted to be the average axial stress calculated as the axial load divided by the cross-sectional area for plain concrete columns
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