Materials and Structures

, Volume 41, Issue 2, pp 311–321

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

DOI: 10.1617/s11527-007-9241-1

Cite this article as:
O’Flaherty, F.J., Mangat, P.S., Lambert, P. et al. Mater Struct (2008) 41: 311. doi:10.1617/s11527-007-9241-1

Abstract

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.

Keywords

Under-reinforcedCorrosionFlexuralDurabilityStructural

Notation

A

Atomic weight of iron

AS

Area of tensile reinforcement

\({A_S^{\prime}}\)

Area of compressive reinforcement (hanger bars)

a

Rebar surface area before corrosion

α

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

b

Breadth of beam section

β

Intercept (or Mt(0)/Mc ratio)

C

Cover to main steel reinforcement

d

Effective depth to main steel

d

Effective depth to compressive steel

δ

Material loss due to corrosion

\({\Updelta \omega}\)

Weight loss due to corrosion

F

Faraday’s constant

Fcc

Force in the concrete in compression

Fsc

Force in the steel in compression

fcu

Compressive strength of concrete

\({f_y^{\prime}}\)

Yield strength of compressive steel

γ

Density of steel

γc

Partial safety factor for the strength of concrete

γs

Partial safety factor for the strength of steel reinforcement

h

Height of beam section

I

Electrical current

i

Corrosion current density

Mc

Maximum moment of resistance of the concrete in the compression zone

Mt(0)

Moment of resistance of the control beam in the tensile zone

Mt(corr)

Moment of resistance of the corroded beam in the tensile zone

Ø

Diameter of the main steel reinforcement

Ø′

Diameter of the compressive steel reinforcement

R

Material loss per year due to corrosion

s

Depth of idealised compressive stress block

T

High yield steel reinforcement

T

Time in years

t

Time in seconds

x

Depth to neutral axis

Z

Valence of iron

z

Lever arm

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