Materials and Structures

, Volume 41, Issue 2, pp 311–321 | Cite as

Effect of under-reinforcement on the flexural strength of corroded beams

  • Fin J. O’Flaherty
  • Pritpal S. Mangat
  • Paul Lambert
  • Elena H. Browne
Original Article


Reinforced concrete beams are normally designed as under-reinforced to provide ductile behaviour i.e. the tensile moment of resistance, Mt(0) is less than the moment of resistance of the compressive zone, Mc. The degree of under-reinforcement (Mt(0)/Mc ratio) can depend upon the preferences of the designer in complying with design and construction constraints, codes and availability of steel reinforcement diameters and length. Mt(0)/Mc is further influenced during service life by corrosion which decreases Mt(0). The paper investigates the influence of Mt(0)/Mc on the residual flexural strength of corroded beams and determines detailing parameters (e.g. size and percentage of steel reinforcement, cover) on Mt(0)/Mc. Corroded reinforced concrete beams (100 mm × 150 mm deep) with varying Mt(0)/Mc ratios were tested in flexure. The results of the investigation were combined with the results of similar work by other researchers and show that beams with lower Mt(0)/Mc ratios suffer lower flexural strength loss when subjected to tensile reinforcement corrosion. Cover to the main steel does not directly influence Mt(0)/Mc and, thus, the residual flexural strength of corroded beams is not normally affected by increased cover. A simplified expression for estimating the residual strength of corroded beams is also given.


Under-reinforced Corrosion Flexural Durability Structural 



Atomic weight of iron


Area of tensile reinforcement


Area of compressive reinforcement (hanger bars)


Rebar surface area before corrosion


Slope of Mt(corr)/Mc against percent of corrosion


Breadth of beam section


Intercept (or Mt(0)/Mc ratio)


Cover to main steel reinforcement


Effective depth to main steel


Effective depth to compressive steel


Material loss due to corrosion

\({\Updelta \omega}\)

Weight loss due to corrosion


Faraday’s constant


Force in the concrete in compression


Force in the steel in compression


Compressive strength of concrete


Yield strength of compressive steel


Density of steel


Partial safety factor for the strength of concrete


Partial safety factor for the strength of steel reinforcement


Height of beam section


Electrical current


Corrosion current density


Maximum moment of resistance of the concrete in the compression zone


Moment of resistance of the control beam in the tensile zone


Moment of resistance of the corroded beam in the tensile zone


Diameter of the main steel reinforcement


Diameter of the compressive steel reinforcement


Material loss per year due to corrosion


Depth of idealised compressive stress block


High yield steel reinforcement


Time in years


Time in seconds


Depth to neutral axis


Valence of iron


Lever arm


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Copyright information

© RILEM has copyright 2007

Authors and Affiliations

  • Fin J. O’Flaherty
    • 1
  • Pritpal S. Mangat
    • 1
  • Paul Lambert
    • 1
  • Elena H. Browne
    • 2
  1. 1.Centre for Infrastructure ManagementSheffield Hallam UniversitySheffieldUK
  2. 2.HalcrowBirminghamUK

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