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Studies on ductility and evaluation of minimum flexural reinforcement in RC beams

Abstract

Some experimental investigations on ductility and prediction of minimum flexural reinforcement in reinforced concrete (RC) beams are reported. The minimum flexural reinforcement was evaluated using optimum ductility in RC beams. Beams of size 100 mm, 200 mm and 400 mm were tested, which were designed with varying percentages of flexural reinforcement i.e. 0.15, 0.30, 0.60 and 1.0. The beams were tested under four-point loading to study the flexural behaviour under uniform bending moment. The experimentally obtained average compressive strength of concrete was 30 MPa. The influence of beam size (depth) on cracking and normalised ultimate flexural strength, ductility and overall average rotation has been studied. The cracking in RC beams is complex phenomenon in small size beams, while the cracking strength decreases as the depth increases beyond 200 mm. The flexural strength of RC beams, from the present study, appears to decrease as the depth increases. The ductility of RC beams increases as the percentage of flexural reinforcement increases. The ductility number has been derived from dimensional analysis using fracture mechanics principles. The ductility of RC beams decreases as the depth of beams increases. An optimum percentage of flexural reinforcement has been established using optimum ductility number, Np, which is equal to 0.20. The minimum flexural reinforcement was found to decrease as the beam depth increases, and decreases as the yield strength of reinforcement increases.

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Abbreviations

a:

A constant obtained from the analysis

A:

Area of c/s of beam

Ag :

Gross area of cross-section

As :

Area of steel reinforcement

b:

A constant obtained from the analysis

c:

A constant obtained from the analysis

h:

Size of the member

Ec :

Modulus of elasticity of concrete

Es :

Modulus of elasticity of steel reinforcement

fy :

Yield strength steel reinforcement

ft :

Tensile strength of concrete

GF :

Fracture energy of concrete

h:

Beam depth

KIc :

Concrete fracture toughness

wc :

Crack opening displacement

ρmin :

Minimum flexural reinforcement

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Correspondence to Gangolu Appa Rao.

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Appa Rao, G., Vijayanand, I. & Eligehausen, R. Studies on ductility and evaluation of minimum flexural reinforcement in RC beams. Mater Struct 41, 759–771 (2008). https://doi.org/10.1617/s11527-007-9280-7

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  • DOI: https://doi.org/10.1617/s11527-007-9280-7

Keywords

  • Ductililty
  • Minimum reinforcement
  • Average rotation
  • Size effect
  • Flexural strength