Guide Specification for the Design of Concrete Bridge ... · Guide Specification for the Design of Concrete ... Applicable Design Guide Specifications/Material Specifications. 17

Guide Specification for the Design of Concrete Bridge Beams Prestressed with CFRP Systems

NCHRP 12-97National Cooperative Highway Research Program

Abdeldjelil Belarbi, PhD, [email protected]

AASHTO T-6 (FRP Composites)Spokane, WAJune 13, 2017

1. Introduction

2. Experimental Research Program

3. Analytical Research Program

4. Draft of Design Guide Specifications

5. Draft of Material Specifications

6. Concluding Remarks

2

Two centuries of technological breakthroughIn structural concrete

Portland Cement

1824J. Aspdin

1867J. Monier

Reinforced Concrete

1933E. Freyssinet

Prestressed Concrete

FRP CompositesFRP in Civil Engineering Applications

1960

s

1900

s

Major FRP Technical Committees

3

FRPin Bridges, was it a dream or a vision?

Leonhardt (1964) ‐ in his “Prestressed Concrete ‐Design and Construction” stated that Freyssinet first mentioned the use of glass fibers or plastics for prestressing in 1938:

”Some day, glass fibres or plastics will be used as tendons for prestressing. This idea was first mentioned by Freyssinet in 1938. In the U.S.A., investigations are already in progress in this connection...

4

RC, 40%

Steel, 29%

PC, 27%

Wood,3.7% Other, 0.6%

Source: www.FHWA.DOT.GOV

5

Prestressed Bridges account for 27% of the US bridge inventory

6

Project Objective

To develop a proposed guide specification, inAASHTO LRFD format, for the design ofconcrete beams prestressed with CFRPsystems for bridge applications for bothpretensioning and post-tensioning.

7

Design Guide Specifications (under review)

Material Specifications (under review)

Final Research Report (in progress)

Design Examples (in progress)

Project Deliverables

Analytical Research Program

CFRP Properties

Small-scale Prisms

Large-scale Girders

Parametric Study &Reliability Analysis

Major Research Tasks

Experimental Research Program

Numerical Simulations& FEM Modeling

8

9

CFRP Bars Seven-Wire CFRP Cables

Diameter: 0.5 inElastic Modulus: 20,900 ksi

Tensile Strength: 255 ksi





Values as provided by the manufacturer

Material Used: CFRP

9

10

Material Used: CFRP Anchorages

Potted type: for tension and harping tests wedge

Potted and Socket Type Anchorage

Socket type: for relaxation tests and post-tensioning

Expansive materialsBar: commercially availableCable: proprietary material obtained from manufacturer

CFRP

Steel pipe

Fabrication

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11

Material Used: CFRP Anchorages

wedge

Wedge and Sleeve Anchorage

Fabrication

CFRP Cable CFRP Bar

wedge

sleeve

wedge

sleeveBuffer material

Buffer material

Step 1:Applying buffer material Step 2:Assembling the fixture Step 3: Applying required pressure

All components provided by the manufacturer

CFRP Bar

CFRP Cable

12

Material Used: CFRP SystemCFRP System = FRP Bars/Cables + Anchors + Couplers

Couplers

CFRP Bar CFRP Cable

CouplersBar: Developed by Research TeamCable: Provided by Manufacturer

Pre-tensioning application Post-tensioning application

12

13

Concrete for Beams and Prisms

Strength: 9-12 ksi

Strength: 15 ksi

Material Used: Concrete, Grout, and Duct

Self-consolidating concrete

Grout for Bonded PT

Duct for PT

13

14

Diameter: 0.6 inElastic modulus: 29,000 ksi

Tensile strength: 60 ksi

Diameter: , , inElastic modulus: 29,000 ksi

Nominal yield strength: 60 ksi

Material Used: Steel Reinforcement Stirrups for Girders

Reinforcement for Deck

Spiral Reinforcement for Prisms and PT End ZonesDiameter: ⁄ in

Elastic modulus: 29,000 ksiTensile strength: 60 ksi

Steel Prestressing for Guide Cable and PrestressingDiameter: 0.6 in


14

15

Material Tests: CFRP System

CFRP Mechanical and Physical Properties

CFRP Harping Properties

CFRP Prestress Relaxation Losses15

16


CFRP Mechanical and Physical Properties Cross-Sectional Properties (Af) Fiber Volume Ratio (Vf) Glass-Transition Temperature (Tg) Moisture Absorption Tension Strength, Modulus of Elasticity, Rupture Strain (fpu, Ef,

pu)

Test Procedures Test Results Applicable Design Guide Specifications/Material Specifications

17

CFRP Mechanical and Physical Properties:Cross Sectional Properties, Af

Purpose

Process• Determined by the immersion method• This method is based on an average area that include all

the sand coating and protective layers• Manufacturers may provide a lower value for Af to

exclude the coating layers (effective area )

Test Specimen:

2 inch

No. of Tests:3/CFRP Type

Test Standard:ASTM D792*ASTM D7205

To determine the cross-sectional area of CFRP cable and bars to be used for the calculation of the modulus of elasticity (Ef) and tension strength (fpu).

18

Results

Sample CFRP Cable∅ 0.6 in

CFRP Cable∅0.76 in

CFRP Bar∅ 0.5 in

Average Test Values (in2) 0.226 0.380 0.232

Manufacturer’s Values (in2) 0.180 0.289 0.196

Difference (%) 20% 24% 18%

Consequences

• Improper calculation of area (Af) affects the determination of Ef and fpu• Design calculations using these Ef and fpu will be affected, accordingly • However the Prestress force will not be affected


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AASHTO Material Specifications (Draft)

2.5.4—Prestressing CFRP Types and Sizes The prestressing CFRP can be utilized in two forms: bars or cables.

Only CFRP bars with monolithic, prismatic cross-section (typically circular), and CFRP cables with seven twisted wires are allowed.

The size of prestressing CFRP bars shall be consistent with standard sizes for steel reinforcing bars given in AASHTO M 31M/M 31 (ASTM A615/A615M.

The size of prestressing CFRP cables shall be consistent with standard sizes for steel prestressing strands as given in AASHTO M 203M/M 203 (ASTM A416/A416M).


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Results Based on Proposed Area Designation

AASHTO Material Specifications (Draft) -- Cont’d

2.5.4—Commentary: Areas of a non-standard diameter Example of 7 wire CFRP cable with d=0.76 in.

Diameter of single wire: . 0.253

Nominal Area of single wire: 0.050 Nominal Area of the cable: 7 0.352


CFRP Cable∅ 0.76 in

CFRP Bar∅ 0.5 in

Average Test Values (in2) 0.226 0.380 0.232

Proposed Values (in2) 0.217 0.352 0.200

Difference (%) 4% 7% 14%


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Purpose

Process

Test Specimen: No. of Tests:3/CFRP Type

Test Standard:ASTM E1131

To determine Vf of CFRP cables and bars for quality control proposed in Materials Specifications.

2 inch

The fiber content by weight was determined using thermal gravimetric analysis (TGA) to obtain the mass of a substance which is heated at a controlled rate in an appropriate environment.

CFRP Mechanical and Physical Properties:Fiber Volume Ratio, Vf

21

22

Results


2.5.1 Fiber ContentWhen ASTM D2584 is used, fiber content shall not be less than the fraction by mass corresponding to 55 percent by volume.



CFRP Bar∅ 0.5 in

Average by weight (%) 83.6 81.3 75.2

Average by volume (%) 70 70 65

CFRP Mechanical and Physical Properties:Fiber Volume Ratio, Vf

23

Purpose

ProcessTg was determined by Differential Scanning Calorimetry (DSC) method

To determine Tg for product control proposed in Material Specifications.


Test Standard:ASTM D 3418

2 inch

CFRP Mechanical and Physical Properties:Glass Transition Temperature, Tg

23

24

Results


2.5.2—Glass Transition TemperatureThe glass transition temperature of the resin shall not be less than 212°F (100°C) using the DMA method and 230°F (110°C) using the DSC method



CFRP Bar∅ 0.5 in

Average Tg in oC 102 118 116

CFRP Mechanical and Physical Properties:Glass Transition Temperature, Tg

24

25

Purpose

ProcessThe water/moisture absorption is calculated as follows:

W = 100 · (Pi – Pd)/Pd

Pi = weights of the sample after immersion Pd = weights of the sample in dry state

To determine the moisture absorption for product control proposed in the Material Specifications.


Test Standard:ASTM D 570

CFRP Mechanical and Physical Properties:Water/Moisture Absorption

2 inch

25

26

Results



CFRP Bar∅ 0.5 in

Average Test Value (%) 0.95 0.58 0.37


2.7.1—Moisture AbsorptionThe individual moisture absorption test results shall be reported and their average shall be less than 1.0 percent.

CFRP Mechanical and Physical Properties:Water/Moisture Absorption

26

27

PurposeTo determine the mechanical properties of CFRP materials and CFRP systems (CFRP Bars/Cables and Anchorage)

Process

Extensometer for deformation measurement

SG* for strain measurement

Load cell

Test Standard:ASTM D7205/D7205M-11 and D3171

3 ft 1 ft1 ft

AnchorageAnchorage CFRP

Test Specimen:

No. of Tests:10/CFRP Type

Test Equipment and Instrumentation:

Internal LVDT to measure

deformation of the CFRP

system

* Did not provide reliable strains for cables because of the twisted profile

CFRP Mechanical and Physical Properties:Tension Strength (fpu), Modulus of Elasticity (Ef ),Rupture Strain (f)

27

28

Strain at Rupture Elastic Modulus (Extensometer)

Specimen Load at Rupture Extensometer Strain Gage(kips) (in./in) (ksi)

1 71.5 NA 0.017 NA2 79.0 NA 0.015 NA3 74.5 NA 0.016 NA4 74.2 NA 0.016 NA5 72.9 NA 0.015 NA6 70.2 NA 0.014 NA7 74.4 0.019 0.017 18,0458 71.1 0.019 0.015 17,2459 75.6 0.020 0.022 17,42010 73.5 0.019 0.017 17,830

Mean (μ) 73.7 0.019 0.016 17,650Standard Deviation (σ) 2.29

μ -3σ 66.8

Sample Diameter Af(in.2)

PDesign (Pu)(kips)

PRupture(kips)

Rupture

(in/in)Ef

(ksi)

Manufacturer N/A 0.60 0.180 60.7 N/A 0.020 22,500NCHRP-12-97 10 0.60 0.217 66.8 73.7 0.019 17,650

Results


CFRP Cable: ∅ = 0. 60 in

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Strain at RuptureElastic modulus (Extensometer) Specimen Load at Rupture Strain Gage Optical

ExtensometerContact

Extensometer(kips) (in./in.)

1 109.5 NA 0.015 NA NA2 109.7 NA 0.017 NA NA3 109.6 NA 0.017 NA NA4 108.3 NA 0.016 NA NA5 108.6 NA 0.018 NA NA6 109.6 0.016 0.017 0.016 19,4607 109.2 0.016 0.017 NA NA8 106.0 0.016 0.020 0.017 17,7109 110.2 0.016 0.017 0.017 18,40010 110.8 0.015 0.017 0.017 18,500

Mean (μ) 109.2 0.016 0.017 0.017 18,510Standard Deviation(σ) 1.31

σ-3μ 105.2


Results (cont’d) CFRP Cable: ∅ = 0. 76 in


PDesign (Pu)(kips)

PRupture(kips)

Rupture

(in/in)Ef

(ksi)

Manufacturer N/A N/A 0.289 N/A N/A N/A 22,700NCHRP-12-97 10 0.76 0.352 105.2 109.2 0.017 18,510

(ksi)

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Rupture Strain at RuptureElastic Modulus(Extensometer) Specimen

Load at Rupture Extensometer Strain Gage

(kips) (in./in)1 54.5 0.013 0.013 20,9602 53.8 0.013 0.017 20,6903 52.7 0.013 0.014 20,2704 54.9 0.013 0.013 21,1105 55.7 0.013 0.014 21,4206 56.0 0.014 0.014 20,0007 56.2 0.015 0.014 18,7308 57.1 0.014 0.014 20,3909 52.8 0.013 0.012 20,31010 55.6 0.013 0.013 21,380

Mean (μ) 54.9 0.013 0.014 20,630Standard Deviation (σ) 1.33

μ -3σ 50.9



PDesign (Pu)(kips)

PRupture(kips)

Rupture

(in/in)Ef

(ksi)Manufacturer N/A 0.5 0.196 50.3 54.1 0.014 20,900

NCHRP-12-97 10 0.5 0.200 50.9 54.9 0.013 20,630

CFRP Bar: ∅ = 0. 50 inResults (cont’d)

(ksi)

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Results (cont’d)

32


AASHTO Design Guide/Material Specifications (Draft)

Tension test (ASTM D7205/ D7205M)Tension test shall provide breaking (rupture) load (PRupture,i) and corresponding rupture strain (εRupture,i)

Number of tests ≥ 10 (Article 2.9.1, Material Specs)

Average of rupture load: ∑ ,

Design load (Pu)= ) - 3σ (Article 1.4.1.2 Design Guide Specs)

Average rupture strain∑ ,

0.15%

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AASHTO Design Guide/Material Specifications (Draft) (cont’d)

Determine Af (Article 2.5.4, Material Specs)

Rupture tensile strength :

Modulus of elasticity :

Design tensile strength

Design tensile strain ( Article 2.6.4, Material Specs)

34


CFRP Harping Properties Effect of Harping Angle Effect of Deviator Diameter Effect of Deviator Material: Steel vs. Teflon


34

35

DeviatorHarping Angles

PurposeTo assess the effects of stress concentration at the deviator location and overall strength reduction due to harping

4º12 º

1 inch diameter deviator used for prestressing steel strands

CFRP Harping Properties:Effects of Harping Angle and Deviator Diameter

35

36

Deviator Effect on CFRP Tension StrengthContact pressure and tension/bending stresses at deviator will cause further reduction of tension strength of prestressing tendon, fpu

Deviator

Combined tension and flexural stresses

Contact pressure


37

Test parameters:

• Deviator size (1in., 2 in., 20 in. and 40in. )

• Deviator material (Steel and Teflon)

• Harping angles (5, 10, 15, 20 degrees)

• CFRP Cable (∅= 0.6 in) and CFRP Bar (∅= 0.5 in)

ProcessTest Specimen:

No. of Tests:36/CFRP Type (3 repetitions per test parameter)

12 ft. VariableVariable

AnchorageAnchorage

CFRP


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Variable harping anglesDeviator

Hydraulic jack

Back-to-back channels

Load cell

Test Set-up:

Process (cont’d)

Jacking Load

Measured Load

2 in. Teflon1 in. Steel

38


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Results


MaterialDeviator Diameter

(in.)

Harping Angle

(Degree)

Breaking Load (kips)

% of Design Tensile

Strength

CFRP Bar∅ = 0.50 in

1 20 3.3 6.70

2 10 15.6 31.2

20 10 22.1 44.2

CFRP Cable∅ = 0.60 in

1 20 18.2 29.8

2 10 33.9 55.7

20 10 42.1 69.2

CFRP bars failed by longitudinal splitting at early load levels

0.60fpu

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Preliminary Conclusions• 1 in. and 2 in.-diameter deviators that are available in the industry will not work• CFRP bars are not recommended to be harped in bridge girders

New Research Directions• Investigate other deviators configurations with larger diameters• These deviators need to be developed and accepted by the industry

20 in.-diameter deviator application

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Preliminary Results%

of D

esig

n Te

nsile

Str

engt

h

0.60fpu

Results for CFRP Cables: ∅ = 0.60 in.

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AASHTO Design Guide Specifications (Draft)

1.4.4—Hold-Down Points and DeviatorsThe hold-down devices that are in contact with prestressing CFRP shall have a curvature corresponding to a diameter not less than 20 in. and shall provide 100 percent retention of the design tensile strength of prestressing CFRP based on provisions of Article 2.6.1 of the material specifications

1.4.4—Commentary :Prestressing CFRP bars shall not be harped, unless the manufacturer provides sufficient documentation to demonstrate the feasibility of retaining 100 percent of the design tensile strength of the prestressing CFRP .


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AASHTO Design Guide Specifications (Draft) (cont’d)

1.9.1.1—Prestressing CFRPs with Angle Points or Curves

On-Going Task


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CFRP Prestress Relaxation Losses Prestress Relaxation Losses of CFRP Bars and Cables Prestress Relaxation Losses of CFRP System (Bars/Cables and Anchorages) Effect of Jacking Stress level Effect of Bars/Cables Lengths


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PurposeTo evaluate time-dependent stress losses and the effects of (i) cable/bar length, (ii) prestressing level, and (iii) anchorage losses on individual cables/bars and CFRP system.

Stre

ssSt

rain

Stress Relaxation

Constant Strain

Time

Time

CFRP Prestress Relaxation Losses:All Parameters Affecting Relaxation losses

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46

Sources of relaxation losses in bars/cables Matrix Relaxation (resin is a polymer with high relaxation characteristics) Fiber Straightening during matrix relaxation Wires straightening in cables Fiber Relaxation if any

CFRP Cable, ∅ = 0.76 in. CFRP Cable, ∅ = 0.60 in.

Irregularity in the fiber alignment during pultrusion process (SEM Test)


46

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Test parameters:• Jacking stress level (0.5, 0.6 and 0.7 fpu )• Prestressing CFRP length (10, 15, 20 ft.) and 1 in. (for anchorage losses.)• CFRP Cable (∅= 0.6 in) and CFRP Bar (∅= 0.5 in)

Test Specimen:


10, 15 and 20 ft. VariableVariable

AnchorageAnchorage

CFRP

Process


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48

CFRP Cable or Bar

Steel HSS reaction frame maintaining constant strain

Load cellL = 10,15 and 20 ft.

Test Set-up


Strain gage0.5fpu0.6fpu0.7fpu

Used for the overall pretress relaxation of the system

Used for loss quantification at the anchors due to CFRP-anchors interfacial bond slip and grout creep

49

Stress relaxation of 15 ft.-long specimens at 0.5, 0.6, and 0.7 fpu (3 repetitions)

Prestressing CFRP Cable (∅ = 0.6 in.) Prestressing CFRP Bar (∅ 0.5 in.)

Results


50

Results (cont’d)


Prestressing CFRP Cable (∅ = 0.6 in.) Prestressing CFRP Bar (∅ 0.5 in.)

Stress relaxation of 10, 15, and 20 ft.-long specimens at 0.6fpu (3 repetitions)

Minimum Length Effect

51

Results (cont’d)


CFRP System Losses CFRP Anchors Losses CFRP Losses

52

Results (cont’d)


CFRP Cables( ∅ = 0.6 in.)

Δ 0.020

0.0066log 24log 24 i)

CFRP Bars (∅ = 0.5 in.)

Δ 0.016

0.0057log 24log 24 i)

fpt = stress in prestressing CFRP immediately after tensioning (ksi)= tensile strength of prestressing CFRP (ksi)

ti = time of tensioning (days)

Relaxation Losses Equations for CFRP System

Include relaxation losses for cables/bars and anchors Valid for post-tensioning application Anchors losses need to be subtracted for pretension application On-going Task

53

Results(Cont’d)


CFRP Cables( ∅ = 0.6 in.)

Δ 0.0200.019

0.0066log 24log 24 i)

CFRP Bars (∅ = 0.5 in.)

Δ 0.0160.013

0.0057log 24log 24 i)

fpt = stress in prestressing CFRP immediately after tensioning (ksi)= tensile strength of prestressing CFRP (ksi)

ti = time of tensioning (days)

Preliminary Relaxation Losses Equations for CFRP

Include relaxation losses for cables/bars Valid for pre-tensioning application Anchors losses are subtracted

54

, K′L 0.55 1 ] Kid

fpt = stress level of prestressing steel strands immediately after transfer (ksi)fpy = yielding strength (ksi), KL = 30 for low relaxation steel and 7 for stress relieved steelti = time at transfer (days)

5.9.5.4.2c—Relaxation of Prestressing Strands (AASHTO 2014)

Intrinsic relaxation for steel strands(to be revised for CFRP cable and bars)

Reduction due to CR and SH of concrete(no proposed revision)


55

Prestressing Type fpt =0.5 fpt =0.6 fpt =0.7

′CFRP Cable(∅ = 0.6 in.)

145 110 95

′CFRP Bar(∅ = 0.5 in.)

215 150 125



1.9.2.5.2—Relaxation of Prestressing CFRPIntrinsic relaxation for prestressing CFRP cables and bars as a system with anchorage losses at any time “t” after tensioning of the strands :

Δ′log 24log 24 i

fpt = stress level of prestressing steel strands immediately after transfer (ksi) ti = time at transfer (days)

56

114 years

5.4 % [CFRP System]3.9 % [CFRP System]


Comparison with AASHTO (2014) Equations

15 % [Steel Strands]

57

114 years

4.8 % [CFRP Only]

2.1 % [CFRP Only]


15 % [Steel Strands]

Comparison with AASHTO (2014) Equations

58

Small-scale Prism Testing

Square Concentrically Prestressed Prisms

Rectangular Flexural Prisms

58

6 in.

6 in.

120 in.

59


Evaluation of Creep and Shrinkage of Concrete Evaluation of Thermal Fluctuation Losses Evaluation of Transfer Length

Square Concentrically Prestressed Prisms


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To evaluate creep and shrinkage losses and validate the current AASHTO equations for the case of SCC use.

Purpose


Test Specimen:

Concrete prisms (6x6 in.) prestressed with CFRP Cable (∅= 0.6 in) and CFRP Bar (∅= 0.5 in)

Process

Square Concentrically Prestress Prisms:Creep and Shrinkage of Concrete

Plain concrete prisms for Shrinkage measurements (4x4 in.)

4 in.12 in.

4 in

.

Test parameters:Jacking stress level (0.5, 0.6 and 0.7 fpu

61

S

S

. u

Results

pStrain

Transfer zoneTransfer zone Constant strain zone

Prestressing CFRP Bar (∅ 0.5 in.)Prestressing CFRP Cable (∅ 0.6 in.)


DEMEC target point

. u. u

62

5.4.2.3—Shrinkage and Creep (AASHTO 2014)These provisions shall be applicable for specified concrete strengths up to 15.0 ksi

5.4.2.3.2—CreepThe creep coefficient may be taken as:

(t,ti)= 1.9×ks×khs×kf ×ktd×ti-0.118

5.4.2.3.3—ShrinkageThe strain due to shrinkage may be taken as :

εsh=ks×khs×kf ×ktd×0.48×10-3

factor for the effect of concrete strength and time development


Concrete creep and shrinkage are independent of prestressing material Valid for concrete strength between 5 to 15 ksi Experimental results will be compared with AASHTO equations

63

Prestressing CFRP Cable (∅ 0.6 in.) Prestressing CFRP Bar (∅ 0.5 in.)


Total Creep and Shrinkage Strains*

*Measured from pre-tensioned prisms

64



Shrinkage Strains*

*Measured from small plain concrete prisms

εsh = ks×khs×kf ×ktd×0.48×10-3

65



Creep Strains*

*By subtracting of the shrinkage strains from total shrinkage and creep strains

(t,ti)= 1.9×ks×khs×kf ×ktd×ti-0.118

66


1.9.2.5—Refined Estimate of Time-Dependent Losses:In accordance with the provisions of Article 5.9.5.4 of the AASHTO LRFD Bridge Design Specifications (2014)

No changes for creep and shrinkage losses


67

lfrpcTl ,

Purpose

Square Concentrically Prestress Prisms:Thermal Fluctuation Losses

Longitudinal effect (α frp,l < 10 αc)

Transverse effect (α frp,t > 10 αc)

l

To determine the thermal fluctuation losses and the effect of the resultingtransverse thermal expansion on CFRP-Concrete and the consequence on thebond between these two materials.

68

Strain measurement inside the environmental chamber

Test parameters:• Jacking stress level (0.5, 0.6 and 0.7 fpu)• Transverse reinforcement• CFRP Cable (∅= 0.6 in) and CFRP Bar (∅= 0.5 in)


Process

3-h at 0° F Time (Hour)Te

mpe

ratu

re (F

)

Square Concentrically Prestress Prisms:Thermal Fluctuation Losses

On-going Task

3-h at 120° F

69

To measure the end zone transfer length of prestress bars and cables.

Purpose

Square Concentrically Prestress Prisms:Transfer Length, lt

Process

ResultsTo be included and shown with the large-scale beam test

Transfer zoneConstant strain zoneTransfer zoneDEMEC target point measurement

8 in.

70


Evaluation of Long-term Deflections Evaluation of Transfer Length

Rectangular Flexural Prisms

Test Procedures Test Results

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Rectangular Flexural Prisms Long-term Deflection

PurposeTo investigate the long-term deflections of concrete beams prestressed with CFRP systems under sustained load and validate the existing calculation methods and provide changes if necessary.

Process

12.0 ft.

2.0 ft. 4.5 ft.4.5 ft. ½ ft.½ ft.

Threaded rodsHSS Roller

supports

Test Specimen:

No of tests:4 beams with CFRP Cable (∅=0.6 in)4 beams with CFRP Bar (∅=0.5 in)

72

Rectangular Flexural Prisms Long-term Deflection

Results

About 40% increase in deflections for both types of CFRP systems after one year of applied sustained loading

Normalized long-term deflection

73

AASHTO Type I

8 inch composite deck

Full Scale Testing

74

Full-Scale Testing Test Matrix Design Approach Beam Configuration and Fabrication Camber Prestress Losses and Transfer Length

Seating Losses Elastic Shortening Losses Friction/Wobble Losses Transfer Length

Flexural Behavior Monotonic Loading Fatigue Loading Crack Patterns

75

Full Scale Testing

Pre-Tension, Straight Bars/Cables [7]

Unbonded [1]

Bonded [2]

Cables ∅ = 0.76 in.) [3]

Cables ∅ = 0.6in.) [3]

Fatigue [1]

Cables ∅ = 0.76 in.) [2]

. ,

Post-Tension, Straight Cables [2]

Post-Tension, Draped Cables [3]

Bars ∅ = 0.5in.) [4]

Monotonic [2]

Partially Debonded [1]Monotonic [3]

Fatigue [1]

Monotonic [1]

Fatigue [1]

Fatigue [1]

Fatigue [1]Monotonic [1]

76

Concrete crushingCompression failure

CFRP ruptureTension failure

Selected Mode of Failure

Full-scale Testing:Design Approach

77


0.6 fpu

Af (in2)

Af,usedAfb,fruAfb,fpu

78


0.6 fpu

Af (in2)

Afb,fru Af,usedAfb,fpu

79

0.6 fpu

Afb,fru (composite)

Af (in2)

Failure Load (Test)

Cracking Load (Test)


Afb,fru Af,usedAfb,fpu

80

Af (in2)

12 ,

of composite beam/deck

Congestion of CFRP anchors


Afb,fru (composite)Af,used

81

Afb,fru

Afb,fru

0.6 fpu

0.7 fpu

Same ultimate capacity!!

Some increase in cracking capacity


Af (in2)

Af,used

82

Full Scale Testing: Beam Configuration and Fabrication

Steel Pre-tensioned Beam


8 steel strands (∅= 0.6 in)Asfpu=470 kips

83

Affru was selected to be the same for CFRP cables and bars

CFRP Pre-tensioned Beams

Affpu=600 kipsAffru=650 kips



84

Post-tensioned, Straight CFRP cables

CFRP Post-tensioned Beams


Post-tensioned, Straight and Draped CFRP cables


85

CFRP Pre-tensioned Beams


86

CFRP Post-tensioned Beams


87

Bonded Post-tensioned Beams

Grout injection at the inlet Grout coming out from Outlet


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Laser-based

Conventional Rule

Potentiometers

Laser-based measurement device

CamberTest Specimen:

Full Scale Testing: Camber

PurposeTo measure the camber of the prestressed beams and compare it with the current AASHTO (2014) provisions.

89

Calculated vs Measured camber for Full-scale beams

AASHTO Design Guide Specifications (Draft) 1.7.3.4.2—Deflection and Camber

Pre-tensioned Beams with CFRP Cables

Pre-tensioned Beams with CFRP Bars

Post-tensioned Beams

The current AASHTO (2014) LRFD will be used for camber calculation

Full Scale Testing: Camber

90

Full-Scale TestingPrestress Losses and Transfer Length

Seating Losses Elastic Shortening Losses Wobble and Friction Losses Prestress Transfer Length

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Load cells attached to the dead end

Dead End

Live End

Load cells attached to the live end

Test Specimen:

Process and Instrumentation:

Prestress Losses and Transfer Length: Seating Losses

PurposeTo measure the seating losses of the prestressed beams and compare it with the current AASHTO (2014) provisions.

The anchorage set losses for the full-scale post-tensioned beams were found to be less than 1.0 percent

AASHTO Design Guide Specifications (Draft) C 1.9.2.2.1—Anchorage Set

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Test Specimens:

Strain gages installed at mid-span of the pre-tensioned beams

Dead End

Live End

Load cells attached to the dead end of post-tensioned beams

Pre-tensioned beams

Post-tensioned beams


Prestress Losses and Transfer Length:Elastic Shortening

To measure the elastic shortening in prestressed beams and compare it with the current AASHTO (2014) provisions.

Purpose

93

AASHTO Design Guide Specifications (Draft) 1.9.2.2.3a—Pretensioned MembersThe loss due to elastic shortening in pretensioned members shall be taken as:

Δ Use existing AASHTO (2014) equation but replace with


94

1.9.2.2.3b—Post-Tensioned MembersThe loss due to elastic shortening in post-tensioned members may be taken as:

∆

Elastic shortening of cable T1 during the posttensioning sequence

T1

M1

B1 B2 B3



Use existing AASHTO (2014) equation but replace with

95

Dead End

Live End Friction

Jacking

Test Specimen:

Process

Prestress Losses and Transfer Length: Wobble and Friction Losses

Wobble Coefficient vs. Jacking force

K=0.0015

ΔfpF=fpj (1-e-(+Kx))

ResultsWobble Coefficient

To quantify the wobble and friction coefficients of the duct/CFRP used for the post-tensioned beams.

2’’ Corrugated plastic ductMaterial: Polypropylene

96

Test Specimen:Dead End

Live End Friction

Jacking

Friction Coefficient vs Jacking force

=0.21

ΔfpF=fpj (1-e-(+Kx))

Wobble Coefficient + Friction Coefficient Results (cont’d)

2’’ Corrugated plastic ductMaterial: Polypropylene


97

Post-Tensioned Construction:ΔfpF=fpj (1-e-(+Kx))

μ = coefficient of frictionK = wobble friction coefficient per unit length of tendon (1/ft.)

5.9.5.2.2—Friction (AASHTO 2014)


Values of K and μ should be based on experimental data In the absence of such data, a value within the ranges of K and μ as

specified in Table 5.9.5.2.2b-1 may be used.

Prestressing Type Type of Duct K μ

Steel Wire or strand

Rigid and semirigid galvanized metalsheathing 0.0002 0.15–0.25

Rigid steel pipe deviators for external tendons 0.0002 0.25

Polyethylene 0.0002 0.23

CFRP Cable Polypropylene 0.0002 0.22

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Test Specimen:

Process

Transfer Length Zone Transfer Length Zone

DEMEC pointsArrangement of DEMEC points at the end of

the beam

Prestress Losses and Transfer Length: Transfer Length

To measure and provide and equation for prestress transfer length for CFRP cables and bars.

99

5.11.4—Development of Prestressing Strand ( AASHTO 2014)


100

Full-scale Beams -- CFRP Cable (∅= 0.6 in.)

Beam 1: lt =22 in. (≅37db )Beam 2: lt =25 in. (≅42 db )

Results (Full-scale Beam Test)

Full-scale eams --CFRP Bar (∅= 0.5 in.)

Beam 1: lt =28 in. (≅56 db )Beam 2: lt =32 in. (≅64 db )

Average Maximum Strain (AMS) line to determine Transfer Length

0.6 , 5.4 ksi 0.57-0.61 , 4.1-5.2 ksi


101

Small-scale Prisms -- CFRP Bar (∅= 0.5 in)

lt =25.5 in. (≅ db) for 0.7 lt =22.0 in. (≅44 db) for 0.6 lt =20.0 in. (≅40 db) for 0.5

Small-scale Prisms -- CFRP Cable (∅= 0.6 in)

lt =24.0 in. (≅40 db ) for 0.7 lt =21.5 in. (≅36 db ) for 0.6 lt =20.0 in. (≅34 db ) for 0.5

Results (Small-scale Prism Tests)

0.49-0.68 , 5.6 ksi0.55-0.72 , 9.5 ksi

0.5 f0.6 f0.7 f


102


1.11.1—Development of Prestressing CFRPBased on ACI440.4R-04*, CAN/CSA S806-12 and SimTREC Manual:

.

prestressing CFRP diameter (in.)concrete compressive strength at prestress transfer (psi)

= effective stress in prestressing CFRP after transfer (psi)= coefficient related to types of prestressing CFRP taken as 10 for bar, 11 for cable


103

Results

.: 10 for CFRP Bar, 11 for CFRP Cable


104

Full-Scale TestingFlexural Behavior

Monotonic Loading Fatigue Loading Crack Patterns

105

Test Setup

∆

P

P/2P/2

Flexural Behavior: Monotonic Loading

106

ResultsLoad-Deflection Behavior

Pre-tensioned Beams



107


Pre-tensioned Beams with CFRP Cables

Pre-tensioned Beams with CFRP Bars



+/- 5%

108

Uncracked Beam

Purpose

Test Specimen:

Fatigue Truck

Cracked Beam

To evaluate the fatigue performance of the CFRP prestressed beams.

Accidental Cracking!

Fatigue Truck

Load Vs Time history of fatigue loading

For Post-tensioned beams the upper Fatigue limit was Cracking Load!

Flexural Behavior: Fatigue Loading

109

Results

Effect of Fatigue Loading on Moment Capacity

Flexural Behavior: Fatigue Loading

Effect of Fatigue Loading on Beam Stiffness

110

Pretensioned with CFRP Bars

Pretensioned Beams

Pretensioned with CFRP Cables

Pretensioned with Steel Strands

Flexural Behavior: Crack Patterns

111

Bonded with CFRP Cables Unbonded with CFRP Cables

Flexural Behavior: Crack Patterns


112

Analysis and Numerical Simulations

Numerical Simulations

Parametric Study and Reliability Analysis:

113

Analysis and Numerical Simulations: Numerical Simulations

1. Calibrate the Finite Element Model2. Carry out a Parametric Study3. Perform a Reliability Analysis for F factor

114

Design CapacityNominal Capacity

Resistance factor (ϕ)

Ductile (Yield)

Brittle (Rupture)

Analysis and Numerical Simulations: Parametric Study and Reliability Analysis

115

Develop a Comprehensive Design Space

Determine nominal load and resistance model for every limit state

Simulate random variables according to distribution model and statistical parameters

Find failure probability and reliability index

Is target reliability achieved?(No)

Output results

Determine random variables and assign statistical descriptor to each of them

(Yes)

Modify resistance

factors

12- Full-Scale tests» 7- Pre-tensioned beam» 5- Post-tensioned beam


Process:

116

Target Reliability Index:

• Adopted as 3.5 for steel prestressed bridges in AASHTO LRFD-2014• CFRP prestressed bridge girders differ from steel prestressed in terms

of ductility and redundancy• Given the nature of failure of CFRP prestressed bridges failing by

CFRP rupture (sudden failure with no residual capacity), the target reliability should be increased

• This can be addressed by using the load modifier (η) as specified in AASHTO LRFD-2014

• The load modifier is a multiplicative combination of three parameters namely ductility (ηD), redundancy (ηR), and operational classification (ηI)

η= ηD× ηR × ηI

• Generally, using η>1, relates to the target reliability higher that 3.5.


117

Preliminary results

Girder location Failure mode Target Reliability

Resistance factor

InteriorTension-controlled

3.5 0.75

3.8 0.65

4 0.6

Compression-controlled 3.5 0.75

Exterior Tension-controlled3.5 0.60

3.8 0.50

Target reliability and Resistance factor for bonded prestressed CFRP systems


118

A standalone document in AASHTO LRFD formatwith commentary

Contains two sections Design Guide Specifications (Section 1) CFRP Material Specifications (Section 2)

119

SCOPE:

• Concrete compressive strengths from 5.0 ksi to 15.0 ksi.

• Pre-tensioned concrete beams

• Bonded and unbonded internally post-tensioned concrete beams.

• Steel transverse reinforcement only.

Provisions for unbonded post-tensioned beams may be applicable to beams that are strengthened with external CFRP post-tensioning.

LIMITATIONS:

• Anchorage detailing for external CFRP post-tensioned strengthening systems

• Partially prestressed concrete beams except that partial prestressing is allowed for beams with unbondedpost-tensioning.

• Segmental construction andprestressed concrete bridgebeams curved in plan.

• Design for torsion.

120

Provisions AASHTO (2014) Guide Specification (Draft)

Stress Limit for CFRP Tendons

Straight Tendons

At jacking:

Pre-tensioned = 0.75 fpuPost-tensioned = 0.9 fpy

At service = 0.8 fpy

At jacking= 0.65 fpuAt service =0.6 fpu

Harped/ Draped N/A (On-Going Task)

Losses

Prestress Relaxation Δf t, tfK′L

log 24tlog 24ti)

ff 0.55

)

′ varies according to prestressinglevel and CFRP type

Creep (t,ti)=1.9×ks×khs×kf ×ktd×ti-0.118 Same as AASHTO

Shrinkage εsh=ks×khs×kf ×ktd×0.48×10-3 Same as AASHTO

Temperature Effect N/A (On−Going Task)

Friction Losses ΔfpF=fpj (1-e-(+kx)) Same with and k modified

Elastic Shortening Δf f →

Anchorage Set ΔfΔASl E →

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Flexural Design

Resistance Factor For tension -controlled: ∅ = 1.0For compression -controlled: ∅ = 0.75

For tension-controlled: ∅ = 0.65For compression-controlled: ∅ = 0.75(On-Going Task)

Min FactoredFlexural Strength

• 1.33Mr

• M γ γ f γ f S M 1 (On-Going Task)

Unbonded Prestressing CFRP

900

22

./

(single point loading)./

(two point, uniform loading or acombination)

Serviceability Limit States

Long-term DeflectionMultiplying instantaneous deflections by;4.0 (for Ig) or3.0 -1.2 (A’s / As ) ≥1.6 (for Ie)

Multiplying instantaneous deflectionsby; 4.0 (for Ig)(On-Going Task)

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Bond, Development Length and

Transfer Length

Transfer Lengthℓ =60 db

.

=10.2 for bar

=11.2 for cable

Development Length23

.

=5.3 for bar

=14.8 for cable

+

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Provisions Test Methods Limitations

PHYSICAL PROPERTIES

Fiber Content • ASTM D3171• ASTM D2584 Shall not be less than 55 percent by volume

Glass Transition Temperature

• ASTM E1356• ASTME1640

• Shall not be less than 212°F (DSC)• Shall not be less than 230°F (DMA)

Coefficients of Thermal Expansion

• ASTM E831 • ASTM D696 N/A

Prestressing CFRP Types and Sizes

• AASHTO M 31M/M 31 (ASTM A615/A615M)

• AASHTO M 203M/M 203 (ASTMA416/A416M)

• ASTM D7205/D7205M

The measured area of the prestressing CFRP barsand cable shall be between 1.0 to 1.2 times thenominal area provided

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MECHANICAL PROPERTIES

Tensile Strength ASTM D7205/ D7205M N/A

Tensile Modulus of Elasticity ASTM D7205/ D7205M

The tensile modulus of elasticity of CFRP bars and cables based on the cross-sectional area, as specified in Article 2.5.4, shall be at least 17,000 ksi.

Shear Strength (Transverse axis) ASTM D7617/ D7617M The transverse shear strength of prestressing

CFRP shall be at least 18 ksi.

Tensile Strain N/AThe tensile rupture strain of CFRP cables and bars obtained by this procedure shall be at least 1.2 percent.

Bond Strength ASTM D7913/D7913M N/A

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DURABILITY PROPERTIES

Moisture Absorption ASTM D570 The individual moisture absorption test resultsshall be reported and their average shall be lessthan 1.0 percent.

Resistance to Alkaline Environment

ASTM D7705/D7705M The strength retention of prestressing CFRP exposed to alkaline environment shall not be less than 90 percent

Longitudinal Wicking ASTM D5117 N/A

Ultra Violet Exposure ASTM G153

The strength retention of prestressing CFRP exposed to ultra violet exposure shall not be less than 95 percent

Freeze-Thaw Cycles ASTM D7792/D7792MThe strength retention of prestressing CFRP exposed to freeze-thaw cycles shall not be less than 95 percent.

Galvanic Corrosion N/A

Adequate precautions shall be taken to prevent galvanic corrosion in internal reinforcing applications with prestressing CFRP.

126


OTHER REQUIREMENTS FOR PRESTRESSING CFRP

Long-Term Relaxation

ACI 440.3R Test Method B.9 N/A

Creep Rupture ACI 440.3R Test Method B.8

N/A

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Most of the current AASHTO provisions are applicable for CFRP Design approach and methodology

Creep, shrinkage and elastic shortening losses

Camber and deflections

Major revisions to be included Harping and draping of Prestressing CFRP

CFRP prestress relaxation losses

Jacking stress limits

Prestress transfer length

Strength reduction factors

128

Various Reduction factors Environmental reduction factor, CE

CE =1.0 (prestressed and internal post-tension)

CE = 0.9 (external exposure with no proper protection)

Initial jacking stress

If ,

,≅ 1 0.65 ∗ ,

If ,

,1.1 0.65 ∗ ,

0.75 ∗ ,

Strength reduction factors,

=0.75 (compression controlled failure)

=0..65-0.75 (tension controlled failure )

129

Strength Reduction FactorFor compression-controlled 1.5 , =0.75

Same as the current AASHTO-LRFD 2014

For tension-controlled , =0.65-0.75

/? ?

Research TeamDr. Mina Dawood, Associate Professor: UHDr. Bora Gencturk, Assistant Professor: UHMr. Prakash Poudel, PhD Candidate: UHMr. Hamidereza Tahsiri, PhD Candidate: UHMr. Mahmoud Reda, PhD Candidate: UHDr. Bora Acun, Postoctoral Fellow: UHMr. Barry Adkins, MS student: UHDr. Sami Rizkalla, Professor: NCSUDr. Henry Russell: Henry G. Russell, Inc.Dr. Wagdy Wassef: Modjeski and Masters, Inc.NCHRP12-97 panel members

Precast Plants and Material SuppliersPrecast/Prestressed Concrete InstituteHeldenfels Enterprises, Inc.East Texas PrecastTokyo Rope, Inc.Pultrall Inc.

13 0

Abdeldjelil Belarbi, PhD, PE,[email protected]

Thank you !

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