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

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Slab DetailsSlab DetailsSlab Details

Without Shear Reinforcement

With Shear Reinforcement

Without Shear Reinforcement

With Shear Reinforcement

Typical CFRP ‘Shearband’

First Series Second Series

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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

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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

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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

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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

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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)

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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

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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