Materials and Structures

, Volume 45, Issue 7, pp 957–975 | Cite as

Adequately FRP confined reinforced concrete columns under axial compressive monotonic or cyclic loading

  • Theodoros C. Rousakis
  • Athanasios I. Karabinis
Original Article


The study presents the experimental behavior of reinforced concrete square section specimens, externally confined by carbon or glass Fiber Reinforced Polymer (FRP) sheets. The columns are subjected to axial compressive monotonic or repeated load-unload cycles gradually increasing up to failure. The research focuses on columns with longitudinal bars which are critical to premature buckling while examining their effect on lower limit cases of strengthening through FRP confinement. Experiments include also plain concrete FRP confined columns and columns with bars adequately supported by transverse steel reinforcement for comparison. External FRP strengthening covers a wide range of volumetric mechanical FRP confinement ratios allowing comparative investigations. A significant variation in the behavior of FRP confined concrete comes up when bars are unstable, for a light external strengthening scheme as well as for monotonic or cyclic loading. The lower limits proposed by existing recommendations for adequate FRP confinement strengthening of columns are examined.


Concrete Steel Composites Fibre-reinforced polymers Confinement Strengthening Columns Cyclic load Unloading Axial 

List of symbols


Compressive strength of unconfined specimen


Compressive maximum stress of specimen (confined or not)


Compressive ultimate stress of specimen (confined or not)


Effective tensile stress at failure of FRP sheet


Axial strain at peak stress of unconfined specimen f co


Lateral strain at peak stress of unconfined specimen f co


Axial strain at maximum stress of specimen (confined or not)


Ultimate axial strain of specimen (confined or not)


Lateral strain at maximum stress f cc


Ultimate lateral strain


Strain at failure of FRP sheet under direct tension


Effective strain at failure of FRP jacket


FRP reinforcement volumetric ratio



The authors wish to thank S&P and Sintecno S.A. for providing FRP reinforcements and resins and Skarlatos S.A. for providing concrete.


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Copyright information

© RILEM 2011

Authors and Affiliations

  • Theodoros C. Rousakis
    • 1
  • Athanasios I. Karabinis
    • 1
  1. 1.Laboratory of Reinforced Concrete, Department of Civil EngineeringDemocritus University of Thrace (DUTh)XanthiGreece

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