confinment presentation.pptx

1. Theoretical stress-strain Model
for Circular Concrete Columns
Confined by GFRP Spiral and
Hoops ( Afifi et al. 2015)
Dr. Ahmad Al-Tarawneh
By :
Shatha E. Taha & Nisreen J. Abu-Shiekh

2. Steel VS Fiber Reinforced Polymer

3. What is Confinement?
• Confinement of concrete is an effective and commonly
used method in strengthening of columns.
• Confining of concrete enhances the ductility.
• Passive and active confinements are two methods for
confining of concrete.

4. Modelling of stress- strain relationship
is necessary for analysis and design to assess the deformability and ductility of
concrete columns.
Confining the concrete columns with transverse reinforcement is a
passive approach to increase their strength and ductility
Several empirical stress–strain relations are suggested for the confined concrete,
based on the regression analysis of relevant experimental results. They are
presented in simple functions and are convenient for use in engineering practice.
Confinement Modelling

5. Steel VS GFRP-Spiral Confinement
Stress-Strain
Can Steel stress-strain relationship be proposed for GFRP?

6. Factors Affecting Confinement Models
• Transverse reinforcement configuration.
• Longitudinal reinforcement ratio.
• Volumetric ratio.​
• The size and spacing of spirals and hoops.

7. Steel Confinement Models
Richart et al.
1928 Model
Mander et al. 1988
Model
Modified Mander
Model
𝑓𝑙𝑎𝑡𝑒𝑟𝑎𝑙 =
2 𝐴𝑠𝑝 𝑓𝑦𝑡
𝑑𝑠 𝑠
for steel confinement Models ( circular Spiral and Hoops)

8. Afifi Confinement Model For Circular Concrete
Columns Confined by GFRP Spirals and hoops
• Afifi et al. (2015) proposed a confinement model to predict the stress- strain behavior of GFRP RC
columns.
• A confinement model was proposed to predict the maximum concrete core stress and
corresponding concrete strain.
• Mander , Modified Mander and the developed Afifi Models were compared for the tested specimens.

9. Afifi et al. 2015
( Specimens Details )

10. Afifi et al. 2015( SpecimensDetails )

11. How does it
work Using Afifi
experimental
steps on Sample
(G4V-3H80)?

12. G4V-3H80 Sample Calculations:
• Cross Section Area (𝐴𝑔) = 70685.83 𝑚𝑚2
• Concrete Compressive strength (𝑓′𝑐)= 42.9 MPa
• Longitudinal Reinforcement Ratio ( 𝜌𝑠)= 1.10
• Transvers Reinforcement Ratio ( 𝜌𝑠𝑡) =1.50
• Confinement method = Spiral
• Spacing (s) = 80 mm Clear Spacing ( 𝑠′
) = 70.5 mm
• Cover = 25 mm
• 𝑑𝑠 = D – 2×Cover - 𝑑𝑠𝑡 = 240.5 mm

13. G4V-3H80 SampleCalculations:
• Core Cross Section Area (𝑨𝒄) = 45427.63 𝑚𝑚2
• 𝜌𝑐𝑐 =
𝐴𝑠
𝐴𝑐
= 1.75
• Area of confined Concrete 𝑨𝒄𝒄 = 𝐴𝑐 ( 1 − 𝜌𝑐𝑐)
𝑨𝒄𝒄 = 44631.63 𝑚𝑚2
• C𝐨𝐧𝐟𝐢𝐧𝐞𝐦𝐞𝐧𝐭 𝐞𝐟𝐟𝐞𝐜𝐭𝐢𝐯𝐞𝒏𝒆𝒔𝒔 𝒄𝒐𝒆𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒕 (𝒌𝒆) = 70685.83 𝑚𝑚2
for spirals 𝑘𝑒 =
( 1−
𝑠′
2 𝑑𝑠
)2
1− 𝜌𝑐𝑐
for Hoops 𝑘𝑒 =
1−
𝑠′
2𝑑𝑠
1−𝜌𝑐𝑐
• 𝒇𝒍𝒂𝒕𝒆𝒓𝒂𝒍 = 𝑘𝑒
2 𝐴𝑠 𝑓𝑓𝑏
𝑑𝑠 𝑠
𝑓𝑓𝑏 𝑖𝑠 𝑡𝑎𝑘𝑒𝑛 𝑎𝑠 𝑡ℎ𝑒 𝑚𝑖𝑛. 𝑜𝑓 ∶
0.004 𝐸𝑡𝑓 and 𝑓𝑙𝑎𝑡𝑒𝑟𝑎𝑙 = 1.21

14. Experimental Results
𝑃𝑚𝑎𝑥 = 2826 𝑘𝑁*
𝑃𝑠𝑝 = 2704 𝑘𝑁*
Ꜫ𝑐𝑐 = 2755 × 10−6*
*Note: Electrical strain gauges and linear variable differential transducers (LVDTs) were used to capture the strain
distributions of the concrete, bars, spirals, and hoops. The specimens were tested under concentric axial loading using an
11,400 kN MTS testing machine

15. Used Equations Justification

16. Experimental Results ( 𝒇′𝒄𝒄 𝒆𝒙𝒑)
• Unconfined Concrete Strength
𝑓𝑐𝑜 = .85 × 𝑓′𝑐
𝑓𝑐𝑜 =0.85 × 42.9 = 36.47𝑀𝑃𝑎.
• FRP Bars Capacity After Cover Spalling
𝑃𝐹𝑅𝑃−𝑠𝑝 = .35 × Ꜫ𝑐𝑐 × 𝐴𝑠 × 𝐸𝐹
𝑃𝐹𝑅𝑃−𝑠𝑝 = .35 × 2755 × 10−6 × 796 × 55.4
= 42.52 𝑘𝑁.
• Concrete Core Capacity After Cover Spalling
𝑃
𝑐𝑜𝑟𝑒−𝑠𝑝= 𝑃𝑠𝑝 − 𝑃𝐹𝑅𝑃−𝑠𝑝
𝑃𝑐𝑜𝑟𝑒−𝑠𝑝= 2704 - 42.52 = 2,661.48 𝑘𝑁
• Maximum confined concrete strength
𝑓′𝑐𝑐 𝑒𝑥𝑝=
𝑃𝑐𝑜𝑟𝑒−𝑠𝑝
𝐴𝑐
𝑓′𝑐𝑐 𝑒𝑥𝑝 =
2,661.48 ∗1000
45427.63
= 58.59 MPa

17. Afifi et al. RegressionEquations
• The Proposed Model Based Equations showing a nonlinear relationship between the increase in
concrete strength and the confinement ratio 𝑓′𝑙 /𝑓′𝑐𝑜 .
• These equations were based on experimental test results which indicated that lateral confinement
was less effective at higher levels of confining pressure.
• The proposed model was calibrated using regression analysis based on interpretation of the test
results in the experimental database.

18. Afifi et al. Regression Equations

19. Afifi et al. 2015( Specimens Details)

20. Experimental and Theoretical Test Results
f'cc Strength Mander Model Modified Mander Model Afifi Model
Range 0.8 to 1.03 0.87 to 1.03 0.92 to 1.08
Avg. 0.96 0.84 0.96
SD 0.04 0.03 0.05
COV% 4.48 3.49 4.70
Confinement strain Mander Model Modified Mander Model Afifi Model
Range 1.11 to 1.52 0.9 to 1.10 0.89 to 1.07
Avg. 1.00 1.31 1.00
SD 0.05 0.10 0.05
COV% 5.41 7.98 5.27
Indication provided inaccurate predictions
of the confined stress and strain
of the tested FRP RC columns
provided a good correlation
between the ratios of
experimental confined stress to
predicted values
provided a good correlation
between the ratios of
experimental confined stress to
predicted values

21. Experimental and Theoretical Test Results

22. Proposed Stress-Strain relationship Model
Ascending Branch
Binge et al. 2001

23. Proposed Stress-Strain relationship Model
Descending Branch
Fafitis and Shah 1985

24. References:
 ACI (American Concrete Institute). (2008). “Guide for the design and construction of externally bonded FRP systems for
strengthening concrete structures.” ACI 440.2R-08, Farmington Hills, MI.
 Afifi, M. Z., Mohamed, H. M., and Benmokrane, B. (2015). “Theoretical stress-strain model for circular concrete columns
confined by GFRP spirals and hoops.” Eng. Struct., 102, 202–213.
 Afifi, M., Mohamed, H., and Benmokrane, B. (2013a). “Axial capacity of circular concrete columns reinforced with GFRP bars
and spirals.” J. Compos. Constr., 10.1061/(ASCE)CC.1943-5614.0000438, 04013017.
 Bing L, Park R, Tanaka H. Stress–strain behavior of high-strength concrete confined by ultra-high- and normal-strength
transverse reinforcements. ACI Struct J 2001;98(3):395–406.
 Fafitis A, Shah SP. Predictions of ultimate behavior of confined concrete columns subjected to large deformations. ACI J Proc
1985;82(4): 423–33.
 Sankholkar, P., Pantelides, C., and Hales, T. (2018). “Confinement Model for Concrete Columns Reinforced with GFRP Spirals”
DOI: 10.1061/(ASCE)CC.1943- 5614.0000843. © 2018 American Society of Civil Engineers.

25. Thank you !