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Centre forCement and Concrete
Punching Shear Behaviour and Design of FRP RC Flat Slabs
Punching Shear Behaviour and Design of FRP RC Flat Slabs
Dr Kypros Pilakoutas, Reader
Dr Abdel Wahab El-Ghandour, ResearcherProfessor Peter Waldron, Pro-Vice Chancellor
Centre for Cement and ConcreteDept. of Civil and Structural Engineering
The University of Sheffield, UK
http://www.shef.ac.uk/~tmrnet
Centre forCement and Concrete OutlineOutline
Why FRP?
Context of Work
Experiments on Flat Slabs
Bond Slip and Punching Shear
Concrete Shear Resistance (FRP RC)
FRP Shear Reinforcement (Predictive Model)
Conclusions
Centre forCement and Concrete Why FRP Reinforcement?Why FRP Reinforcement?
Chloride PenetrationChloride Penetration
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
0.7000
12 25 37.5 50 75
Depth (mm)
Chl
orid
e %
of C
oncr
ete
5 Years10 Years20 Years30 Years40 Years50 Years
Centre forCement and Concrete
1000
2000σ
ε
(MPa)
0 1 2 3 4 5Conventional r/ment
Prestressing wireAFRP
GFRP
Concrete
CFRP
What is FRP Reinforcement?What is FRP Reinforcement?
Centre forCement and Concrete Types of FRP ReinforcementTypes of FRP Reinforcement
Hughes Brothers
EUROCRETE
ARAPREECOMPOSE
FiBRA
UD Tape
Mitsubishi
NEFMAC
LEADLINE
NACC Strand
TECHNORA ROD
C-Bar
Centre forCement and Concrete ApplicationsApplications
Centre forCement and Concrete
Context Of WorkContext Of Work• Eurocrete Project
• Aim: Durable FRP Reinforcement• Partners: 9 Companies + University of Sheffield• Funds: 5.6 million ECU
• fib TG 9.3 + ConFibreCrete Research Network• Aim: Design Guidelines• Members: Over 40 International Experts• TMR: 11 Institutions from 9 EC Countries• Funds: 1.3 million Euro
Training and Mobility of Researchers http://www.shef.ac.uk/~tmrnet
Centre forCement and Concrete
Research on FRP ReinforcementResearch on FRP Reinforcement
ResistanceR
PS,
R (
S,R
)
S = R ∴ LimitState
S>R ∴Failure
S < R ∴Safe
Design Philosophy
Flexure and Cracking
Punching Shear
Shear
Bond
Pre-cast Concrete
Centre forCement and Concrete
Slab DetailsSlab DetailsSlab Details
Without Shear Reinforcement
With Shear Reinforcement
Without Shear Reinforcement
With Shear Reinforcement
Typical CFRP ‘Shearband’
First Series Second Series
Centre forCement and Concrete
RC Slab Design and TestingRC Slab Design and TestingRC Slab Design and Testing
Loading Frame
Slab
FLAT SLAB TESTING
Reaction Frame
22.5 o
DESIGN OF SLABS
CriticalPattern
Slab SCS1
Centre forCement and Concrete
Compression side
Tension sideSplitting Crack
Column
FRP Reinforcement
Slab SGS1 at Failure
Bond Slip and Crack LocalisationSlabs of the First Series
Bond Slip and Crack LocalisationBond Slip and Crack LocalisationSlabs of the First SeriesSlabs of the First Series
Centre forCement and Concrete
Bond Slip and Crack LocalisationSlabs of the First Series
Bond Slip and Crack LocalisationBond Slip and Crack LocalisationSlabs of the First SeriesSlabs of the First Series
0
50
100
150
200
250
-200 1800 3800 5800 7800 9800Microstrain
Loa
d (k
N)
SG1SC1SGS1SCS1
0
50
100
150
200
250
0 10000 20000 30000 40000 50000 60000Microstrain
Loa
d (k
N)
SG1SC1SGS1SCS1 Tension
Strains in Flexural Bars
Concrete Strains
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Punching Shear FailureSlabs of the Second SeriesPunching Shear FailurePunching Shear FailureSlabs of the Second SeriesSlabs of the Second Series
Section through Slab SG3 at Failure
Section through Slab SGS2 at Failure
Section through Slab SC2 at Failure
Centre forCement and Concrete
Punching Shear FailureSlabs of the Second SeriesPunching Shear FailurePunching Shear FailureSlabs of the Second SeriesSlabs of the Second Series
0
50
100
150
200
250
300
350
-500 1500 3500 5500 7500Microstrain
Loa
d (k
N)
SG2SG3SC2SGS2
0
50
100
150
200
250
300
350
-500 1500 3500 5500 7500 9500Microstrain
Loa
d (k
N)
SG2SG3SC2SGS2 Tension
Strains in Flexural Bars
Concrete Strains
Centre forCement and Concrete
The concrete section does not recognize what it is reinforced with,but only experiences forces and strains.
BS 8110vc = (100 Ae / bv d)1/3 (400 / d)1/4 (0.27) (fcu)1/3 ,
Strain ApproachStrain Approach Ae = AFRP (EFRP / Esteel)
StresStresss ApproachApproach Ae = AFRP (σFRP / σyield steel )
Modified ApproachModified Approach Ae = AFRP (EFRP / Esteel) (Φ)Φ = εFRP / εyield steel
when εFRP = 0.0045, Φ = 1.8
Concrete Shear ResistancePredictive Approaches
Concrete Shear ResistanceConcrete Shear ResistancePredictive ApproachesPredictive Approaches
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Concrete Shear ResistancePredictive Approaches
Experimental & BS Predicted Capacities of SG2
Concrete Shear ResistanceConcrete Shear ResistancePredictive ApproachesPredictive Approaches
Experimental & BS Predicted Capacities of SG2Experimental & BS Predicted Capacities of SG2
0
100
200
300
400
500
0 200 400 600 800 1000
Stress (MPa)
Loa
d (k
N)
Experimental Failure Load versus:Maximum Bar Stress in Critical RegionAvgerage Bar Stress in Critical RegionPredicted Stress in Critical Section
Predicted Capacity (Strain App.)
Predicted Capacity (Modified App.)
Punching Shear Capacity Envelope (Stress Approach)
Flexural Capacity versus Stress in Bars
Predicted Capacity (Stress Approach)
Centre forCement and Concrete
0
100
200
300
400
500
0 200 400 600 800 1000
Stress (MPa)
Loa
d (k
N)
Experimental Failure Load versus:Maximum Bar Stress in Critical RegionAverage Bar Stress in Critical RegionPredicted Stress in Critical Section
Predicted Capacity (Strain App.)
Predicted Capacity (Modified App.)
Punching Shear Capacity Envelope (Stress Approach)
Flexural Capacity versus Stress in Bars
Predicted Capacity (Stress Approach)
Concrete Shear ResistancePredictive Approaches
Experimental & BS Predicted Capacities of SG3
Concrete Shear ResistanceConcrete Shear ResistancePredictive ApproachesPredictive Approaches
Experimental & BS Predicted Capacities of SG3Experimental & BS Predicted Capacities of SG3
Centre forCement and Concrete
0
100
200
300
400
500
0 200 400 600 800
Stress (MPa)
Loa
d (k
N)
Experimental Failure Load versus:Maximum Bar Stress in Critical RegionAverage Bar Stress in Critical RegionPredicted Stress in Critical Section
Predicted Capacity (Strain App.)
Predicted Capacity (Modified App.)
Punching Shear Capacity Envelope (Stress Approach)
Flexural Capacity versus Stress in Bars
Predicted Capacity (Stress Approach)
Concrete Shear ResistancePredictive Approaches
Experimental & BS Predicted Capacities of SC2
Concrete Shear ResistanceConcrete Shear ResistancePredictive ApproachesPredictive Approaches
Experimental & BS Predicted Capacities of SC2Experimental & BS Predicted Capacities of SC2
Centre forCement and Concrete
FRP Shear ReinforcementPredictive Model
FRP Shear ReinforcementFRP Shear ReinforcementPredictive ModelPredictive Model
P. S. Capacity Experimental Conventional Proposed
Concrete Contribution
Reinforcement Contribution
SGS2 Capacity (kN)
Spacing of Reinforcement
(vc) (u) (d) ,vc = concrete shear resistanceu = critical perimeterd = effective depth
(n) (εFRP EFRP) (A) ,n = number of vertical legsεFRP = strain at P.S. failureE = modulus of elasticityA= cross sectional area
εFRP = 0.0041εFRP = 0.0025
(Conservative)
εFRP = (Φ) (0.0025)Φ = 1.8εFRP = (0.0045)
(Good)
vc (Strain App.)
(Conservative)(0.5) vc (Modified)
(Good)
270 286(Unconservative)
272(Good)
Only One Layer of Shear Reinforcement was Fully Activated
0.75 d(Unconservative) 0. 5 d
Centre forCement and Concrete
• Bond Slip and Crack Localisation (first series)
• Punching Shear Failure (second series)
• Concrete Shear Resistance
• Strain Approach is Conservative
• Stress Approach offers Upper Limit• Sheffield Method offers Good Predictions
(Strain Correction Factor Φ = 1.8)
CONCLUSIONSCONCLUSIONSCONCLUSIONS
Centre forCement and Concrete CONCLUSIONSCONCLUSIONSCONCLUSIONS
• FRP Shear Reinforcement
• Concrete Contribution = vc(mod. app) / 2
• ε(shear reinforcement) = (0.0025) (Φ = 1.8)
• Max. Spacing of Shear Reinforcement = 0.5 d