Tests of Square Short RC Columns Confined with Steel Straps Under Monotonic Concentric Loading

Tests of square short columns confined with steel straps are reported in this study. A temporary confining method that can be implemented in a short period of time with benefits of increased strength, ductility, and energy dissipation is proposed for square reinforced concrete (RC) short columns within the scope of the research. The method was based on the confining of columns with steel straps as transverse reinforcement. Twelve columns with a scale of 1/3, including three reference and nine strengthened specimens, were tested under axial monotonic loading. The longitudinal reinforcement ratios of columns and the steel strap spacing were the test parameters. The results indicated improvement in terms of strength, ductility, and energy dissipation. Consequently, this method is claimed to have the potential to be adopted for temporary strengthening of columns in the future.

NSC:

Normal strength concrete

HSC:

High strength concrete

SU:

SheikhUzumeri

LP:

Legeron–Paultre

PTMS:

Post-tensioning metal strap

SMA:

Shape memory alloy

A _s :

Area of confining reinforcement

A _e :

Effectively confined concrete area

A _cc :

Concrete core area

A _shy :

Total area of transverse reinforcement in y-direction in Legeron–Paultre Model (similar to A_sy)

A _sx :

Confinement reinforcement area in x direction

A _sy :

Confinement reinforcement area in y direction

ρ:

Longitudinal reinforcement ratio

ρ_st :

The volumetric confining reinforcement ratio

f _c′:

Compressive strength of standard cylinder concrete

f _cc′:

Confined compressive strength of concrete in general and in Legeron–Paultre Model

fcc:

Confined compressive strength of concrete in Sheikh–Uzumeri model

f _c0′:

Unconfined maximum compressive strength of concrete

f _l :

Uniform distributed lateral confinement value

f _yt :

Strength of confining reinforcement

f _le :

Equivalent lateral confinement value

f _h :

Stress in confinement reinforcement

f _hy :

Yield strength of transverse reinforcement

\(f_{{\text{h}}}^{^{\prime}}\) :

Stress in confinement reinforcement at peak strength

b _c, d _c :

Side of the confined core area which is calculated from the center to center of the confining reinforcements.

b _cx :

b_C length in x direction

b _cy :

b_C length in y direction

E _ct :

Tangent modulus of elasticity of unconfined concrete

k :

Parameter in Legeron–Paultre Model

K _s :

Strength gain factor

K ₀ :

Equivalent lateral confinement value coefficient

\(k_{1}^{{{\text{LP}}}}\) :

Parameter in descending branch of stress–strain behavior in Legeron–Paultre model

\(k_{2}^{{{\text{LP}}}}\) :

Parameter in descending branch of stress–strain behavior in Legeron–Paultre model

K _e :

Geometrical confinement effectiveness coefficient

k ₁ :

Lateral compression level factor

k ₂ :

Correction factor for lateral confinement distribution

k ₃ :

Standard cylindrical compressive strength reduction factor

s _l :

Spacing between longitudinal reinforcements (center to center)

s :

Spacing between confining reinforcements (center to center)

s′:

The clear distance between confining reinforcements

w _i′:

iTh clear distance between longitudinal reinforcements

α :

Angle between b_c and the confining reinforcement

δ ₀ :

Displacement that corresponds to the maximum load of the reference column

\(\delta_{0}^{y}\) :

Displacement that corresponds to the yield point of the reference column

\(\delta_{0}^{85}\) :

Displacement that corresponds to 85% of maximum load in descending branch in the reference column

\(\delta_{ex}^{y}\) :

Displacement that corresponds to the yield point of the strapped column

δ _ex :

Displacement that corresponds to the maximum load of the strapped column

\(\delta_{ex}^{85}\) :

Displacement that corresponds to 85% of maximum load in descending branch in the strapped column

δ ₁ :

Displacement that corresponds to the P₁ load in Sheikh–Uzumeri model

δ ₂ :

Displacement that corresponds to P₂ load in Sheikh–Uzumeri model

δ ₁ ³⁰ :

Displacement value that corresponds to 30% of peak load P₁ in Sheikh–Uzumeri model

δ ₂ ³⁰ :

Displacement value that corresponds to 30% of peak load P₂ in Sheikh–Uzumeri model

δ _PL :

Displacement that corresponds to the P_PL peak load in Legeron–Paultre Model

\(\Delta_{0}^{1}\) :

First ductility factor of the reference column

\(\Delta_{0}^{2}\) :

Second ductility factor of the reference column

\(\Delta_{ex}^{1}\) :

First ductility factor of the strapped column

\(\Delta_{ex}^{2}\) :

Second ductility factor of the strapped column

ε _s1 :

Strain corresponding to f_cc in Sheikh–Uzumeri model

ε _c0 :

Strain corresponding to maximum stress in plain concrete

\(\varepsilon_{{\text{c}}}^{{\prime}}\) :

Strain corresponding to f_c′ in Legeron–Paultre Model

\(\varepsilon_{{{\text{cc}}}}^{{\prime}}\) :

Strain corresponding to f_cc′ in Legeron–Paultre Model

ε _cc50 :

Strain corresponding to 0.5 f_cc′ in Legeron–Paultre Model

ε _h :

Strain in transverse reinforcement

ε _s2 :

Strain corresponding to the end point of the plateau defined as in Sheikh–Uzumeri model

ε _s85 :

Strain corresponding to 85% of f_cc in the post-peak region in Sheikh–Uzumeri model

ε _u :

Ultimate strain value in bilinear simplified steel model

ε _y :

Yield strain value in bilinear simplified steel model

ε _c50u :

Unconfined concrete strain corresponding to 50% of the peak stress and is assumed equal to 0.004

σ _u :

Ultimate strength value in bilinear simplified steel model

σ _y :

Yield strength value in bilinear simplified steel model

n :

Number of longitudinal reinforcements

t :

Strap width

\(I_{{\text{e}}}\) :

Effective confinement index

I _e50 :

Effective confinement index at post-peak strain ε_cc50

ρ_sey :

Effective volumetric ratio of transverse reinforcement in y-direction in Legeron–Paultre Model

ρ_cc :

Longitudinal reinforcement ratio Legeron–Paultre Model

\(P_{0}^{y}\) :

Yield load of the reference column

P ₀ :

Maximum load of the reference column

\(P_{0}^{85}\) :

85% Of maximum load of the reference column on the descending branch

\(P_{{{\text{ex}}}}^{y} { }\) :

Yield load of the strapped column

P _ex :

Maximum load of the strapped column

\(P_{{{\text{ex}}}}^{85}\) :

85% Of maximum load of the strapped column on the descending branch

P _0cc :

Axial load capacity of plain concrete of the cross section.

P ₁ :

Starting load of the yield plateau in Sheikh–Uzumeri model

P ₂ :

Ending load of the yield plateau in Sheikh–Uzumeri model

P _PL :

Peak load of Legeron–Paultre Model

This study was funded by Gazi University Scientific Research Projects Coordination Unit, under grant number 06/2012-15.

Authors and Affiliations

1. Department of Civil Engineering, Engineering Faculty, Gazi University, Ankara, Turkey

   Çağatay Mehmet Belgin

Contributions

CMB involved in methodology, funding acquisition, conceptualization, software, visualization, validation, writing—original draft, writing—review and editing.

Corresponding author

Correspondence to Çağatay Mehmet Belgin.

Conflict of interest

The author declares that he has no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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