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Flexural ductility of high-strength concrete columns with minimal confinement

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Abstract

The use of high-strength concrete (HSC) instead of normal-strength concrete (NSC) in columns has the advantage of allowing the column size to be reduced and is thus becoming popular. However, since HSC is more brittle than NSC, its use could result in undesirable brittle failure. To evaluate the ductility of columns, nonlinear moment–curvature analysis taking into account the stress-path dependence of the steel reinforcement is required. Based on such analysis, a parametric study has been conducted to investigate the effects of various factors on the ductility of columns. The results revealed that the effect of concrete strength is dependent on the axial stress level (axial load to area ratio) and axial load level (axial load to capacity ratio). At the same axial stress level, the use of HSC has little or basically no adverse effect on the ductility but if the same axial load level is maintained to reduce the column size, the use of HSC would significantly reduce the ductility. Finally, two formulas for direct evaluation of the ductility of columns are developed.

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Abbreviations

A g :

Area of column section (A g  = bh)

A s :

Total area of longitudinal steel reinforcement

A sb :

Area of balanced steel reinforcement

A sc :

Area of compression steel reinforcement

A st :

Area of tension steel reinforcement

b :

Breadth of column section

d i :

Depth to centroid of steel at ith layer from extreme compressive fibre

d n :

Depth to neutral axis

E c :

Elastic modulus of concrete

E s :

Elastic modulus of steel reinforcement

h :

Total depth of the column section

M p :

Peak moment

P :

Axial load applied at centroid

(P/A g f co ) b :

Balanced axial load level

f co :

Peak stress on stress–strain curve of concrete

f ci :

Stress at inflection point on descending branch of stress–strain curve

f cu :

Cube strength of concrete

f y :

Yield strength of steel reinforcement

ε c :

Strain in concrete

ε co :

Strain at peak stress on stress–strain curve of concrete

ε ci :

Strain at inflection point on descending branch of stress–strain curve

ε ps :

Residual plastic strain in steel reinforcement

ε s :

Strain in steel

ϕ :

Curvature of column section

ϕ u :

Ultimate curvature

ϕ y :

Yield curvature

μ :

Curvature ductility factor

ρ :

Longitudinal steel ratio (ρ = A s /A g )

σ c :

Stress in concrete

σ s :

Stress in steel reinforcement

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Authors and Affiliations

  1. Department of Civil Engineering, The University of Hong Kong, Pokfulam, Hong Kong

    J. Y. K. Lam, J. C. M. Ho & A. K. H. Kwan

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  1. J. Y. K. Lam
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  2. J. C. M. Ho
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  3. A. K. H. Kwan
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Correspondence to J. C. M. Ho.

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Lam, J.Y.K., Ho, J.C.M. & Kwan, A.K.H. Flexural ductility of high-strength concrete columns with minimal confinement. Mater Struct 42, 909–921 (2009). https://doi.org/10.1617/s11527-008-9431-5

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  • DOI: https://doi.org/10.1617/s11527-008-9431-5

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