Guide Specification for the Design of Concrete Bridge...

Guide Specification for the Design of Concrete Bridge

Beams Prestressed with CFRP Systems

NCHRP 12-97 National Cooperative Highway Research Program

Principal Investigator : Dr. Abdeldjelil Belarbi

AASHTO T-6 (FRP Composites)

Saratoga, NY

April 20, 2015

Outline

2

- Project Overview

- Progress of the Project

- Draft Guide Specification

- Template for Material Specification

- On-Going Activities

1925 1950 1975 20001825 1850 1875 1900 2025

1867

J. Monier

1957

Montaso

1933

E. Freyssinet

Reinforced

Concrete

RC vs PC vs FRP

FRP

Prestressed

ConcretePortland

Cement

1824

J. Aspdin

Two centuries of technological breakthrough

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...

FRP in Bridges, was it a dream or a vision?

The Objective of NCHRP 12-97

Develop a proposed guide specification, in AASHTO

LRFD format, for the design of concrete beams

prestressed with CFRP systems for bridge applications

for both pretensioning and post-tensioning.

5

Phase I:

(6 Months)

Phase II:

(30 Months)

Final Report and Guide

Specification

Two-phase project

NCHRP 12-97 Program – OVERVIEW

6

NCHRP 12-97 Program – Phase I

Task 1 • Synthesis of Practice

Task 2

• Items Necessary for Developing Guide Specification

Task 3 • Tentative Outline of the Guide Specification

Task 4 • Interim Report

7

NCHRP 12-97 Project Program – Phase II

Task 6

• Experimental Program

Task 7

• Revised Guide Specification

Task 8

• Design Examples and Template of Material Specification

Task 9

• Final Report

8

• Collection of all available literature, Around 150 reference documents collected

• Conducting a survey to assess current practice, A questionnaire was prepared and circulated to DOT Bridge

Engineers. 34 responses received.

• Collection of data from experimental research activities A database of 258 tested beams from 39 studies.

• Comparison of existing design guidelines

• Compiled a list of bridges constructed with CFRP prestressing


Overview

Synthesis of Practice 9


Experimental Database

A total number of 258 beams were compiled within the database and classified under categories shown above

Synthesis of Practice 10

Prestressing Details Additional Reinforcement Beam Details

Failure ModesMethod Bond

StrandProfile

Tendon Diameter

Non-Prestressed

Shear Reinforcement

Overall Depth

Cross-Section

Span Length

Loading set-up

Shear Span-to-Depth

Ratio

Pre

Po

st

Bo

th

Bo

nd

ed

Un

bo

nd

ed

Bo

th

Stra

igh

t

Dra

pe

d/H

arp

ed

Bo

th

D≤

⅜in

⅜in

<D

≤½

in

D>

½in

No

tR

ep

ort

ed

No

ne

CFR

P

Oth

er

FRP

Ste

el

No

ne

CFR

P

Oth

er

FRP

Ste

el

No

tR

ep

ort

ed

H≤

10

in1

0in

<H

≤2

0in

H>

20

in

Re

ctan

gula

r

I-B

eam

T-B

eam

Oth

er(

Bo

x,Sl

ab,L

igh

tP

ole

)

L≤

15

ft

15

ft<

L≤

30

ft

L>

30

ft

Mo

no

ton

icFl

exu

re

Fle

xure

Fati

gue

She

ar

Fle

xure

and

To

rsio

n

a/d

≤2

.5

2.5

<a/

d≤

5

5<

a/d

≤7

.5

a/d

>7

.5

No

tR

ep

ort

ed

Fle

xura

lTe

nsi

on

Fle

xura

lCo

mp

ress

ion

She

ar

Oth

er(

Bo

nd

slip

,An

cho

rage

)

No

tR

ep

ort

ed

14

6

98

14

19

3

45

20

22

8

23

7 13

8

57

18

45

95

57

12

94

62

34

8 14

0

14

14

41

02

12

18

0

13

42

23

20

9

40

9 18

1

40

27

10

13

72

49

61

63

11

4

41

36

51

16

.

Existing Design

ACI 440.4R-04 (2011)

CAN/CSA-S6-06 (2006)

CAN/CSA-S806-12 (2012)

Guidelines

ISIS Design Manual 5 (2008)

Japanese JSCE CES23 (1997)

fib Bulletins No:40, 65 and 66 (2007;2012)


11 Evaluation of Collected Information

OUTLINE of AASHTO

SPECS

12

1.0—SCOPE

2.0—DEFINITIONS

3.0—NOTATION

4.0—MATERIAL PROPERTIES

4.1—CFRP Bars

4.2—Prestressing Strand

4.3—Post-Tensioning Anchorages and Couplers

4.4—Ducts

4.5—Hold-Down Points and Deviators

5.0—LIMIT STATES

5.1—Fatigue Limit State

5.2—Resistance Factors

6.0—DESIGN CONSIDERATIONS

7.0—DESIGN FOR FLEXURAL AND AXIAL FORCE EFFECTS

7.1—Assumptions for Strength and Extreme Event Limit States

7.1.1—General 7.2—Flexural Members

8.0—SHEAR AND TORSION

8.1—Shear Design

9.0—PRESTRESSING 9.1—Stress Limitations for Prestressing Tendons

9.2—Loss of Prestress

10.0—DETAILS OF REINFORCEMENT 10.1—Minimum Spacing of Prestressing Tendons and Ducts

10.2—Pretensioned Anchorage Zones

11.0—DEVELOPMENT AND SPLICES OF REINFORCEMENT

11.1—Development of Prestressing Strand

12.0—DURABILITY

13.0—SPECIFIC MEMBERS

14.0—PROVISIONS FOR STRUCTURE TYPES


Comparison with existing guidelines

- Same - has provision for - doesn’t have provision for

13

ISIS

Des

ign

Man

ual

CA

N/C

SA

S806

-12

CA

N/C

SA

S06

-06

JS

CE

CE

S23

Mod

el C

od

e 2010

AC

I 440.4

R-0

4

AA

SH

TO

LF

RD

*fo

r st

eel

ten

don

s

NC

HR

P 1

2-9

7

Specification

Subtask

No

Outline

Section

Stress Limit

for CFRP

Tendons

Straight Tendons 6.1

6.6

5.0

9.1

At jacking 0.70ffrpu (pre/post)

At transfer 0.65ffrpu (pre/post)

Harped/ Draped 6.1

6.6

4.5

9.1

Stress increase due to harping,

ch

frp

hR

yE

Losses

Elastic

Shortening 6.3

6.4 9.2 cir

ci

pf

E

EES for pretensioned

Creep (6.4) (9.2) cdscir

c

p

cr ffE

EKRHCR

201.077.037.1

Shrinkage 6.4 9.2 SH = 117- 1.05 RH, for pretensioned

SH = 94 – 0.85 RH, for post-tensioned Relaxation 6.3 9.2 REL = REL1 + REL2 + REL3

Friction Losses (6.6) (9.2) Px=Pj e-(+x)

Anchorage

Seating Loss 6.3 9.2

L

EP

frpAS

AS

Temperature

Effect 6.4 9.2 frpcfrpT ETP




14

IS

IS D

esig

n M

an

ual

CA

N/C

SA

S806

-12

CA

N/C

SA

S06

-06

JS

CE

CE

S23

Mod

el C

od

e 2010

AC

I 440.4

R-0

4

AA

SH

TO

LF

RD

*fo

r st

eel

ten

don

s

NC

HR

P 1

2-9

7

Specification

Subtask

No

Outline

Section

Flexural

Design

Material

Resistance

Factor for

CFRP

6.6 5.2

frp= 0.85 (pretensioned),

= 0.85 (post-tension, bonded)

= 0.80 (post-tension, unbonded)

= 0.75 (bridge tendons) Stress Strain

for CFRP 6.6

4.0

4.1

4.2

Linear

Min Factored

Flexural

Strength 6.6 7.0

Mr 1.5 Mcr or

Mr 1.5 Mf

Serviceability

Limit States

Long Term

Deflection N/A N/A

Modifiers for CFRP Tendons;

= 1.85 (due to self-weight at erection)

= 2.70 (due to self-weight at final)

= 4.10 (due to applied loads at final Fatigue 6.6 5.1 No significant effect for uncracked members

Ductility /

Deformability

Ductility N/A N/A

1

2

1

el

tot

E

E

Deformability 6.6 4.0

frps

frpu

ad

kdd

1


Evaluation of Collected Information



15

ISIS

Desi

gn

Man

ual

CA

N/C

SA

S806

-12

CA

N/C

SA

S06

-06

JS

CE

CE

S23

Mod

el

Cod

e 2

010

AC

I 440.4

R-0

4

AA

SH

TO

LF

RD

*fo

r s

teel

ten

don

s

NC

HR

P 1

2-9

7

Specification

Subtask

No

Outline

Section

Shear Design 6.6 8.0

8.1

pFRPvvccpFRPstcr VdbfVVVV 25.0

Equation for Vc, Vst and Vp,frp differs according to

code

Bond, Development

Length and Transfer

Length

6.5

6.6

11.0

11.1

Ld= Lt + Lfb where,Transfer length, Lt

67.0

cit

tpi

tf

dfL

(in mm) for CFRP

Flexural bond length, Lfb

67.0

cf

tpefrpu

fbf

dffL

(in mm) for CFRP

Unbonded

Prestressing 6.6 14.0 frpu

u

p

cupupep fc

dEff 8.01

GUIDE SPECIFICATION

16

A draft version of the guide specification for the design of concrete beams

prestressed with CFRP systems is developed.

• Contains two sections; • Provisions of draft guide specification (Section 1)

• Template for material specification (Section 2)

• A standalone document in AASHTO LRFD format with

commentary, • Future revisions to the AASHTO LRFD Specification (within the

project period) will be also considered for developing guide

specification with the approval of the NCHRP.

• The commentary with its current state serve for two purposes; Background information for the articles that are either complete

or need further explanation,

List of subtasks of the Phase II work plan that are necessary to

address the specific articles

17

NCHRP 12-97 Project Program – GUIDE SPECIFICATION

18


SCOPE:

• Concrete compressive strengths

from 4.0 ksi to 15.0 ksi.

• Pretensioned 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 unbonded post-tensioning.

• Segmental construction and

prestressed concrete bridge

beams curved in plan.

• Design for torsion.

19

NCHRP 12-97 PROJECT PROGRAM – Prestressing CFRP

Highway Bridge on

I-10 in New Orleans

An example of external post-tensioning with prestresing CFRP cable

with twisted wires.

20


Outline of the Draft Guide

Specification

(Section 1)

1.8—DESIGN FOR SHEAR 1.8.1—SHEAR DESIGN 1.8.2—GENERAL REQUIREMENTS 1.8.3—SECTIONAL DESIGN MODEL

1.9—PRESTRESSING 1.9.1—STRESS LIMITATIONS FOR PRESTRESSING CFRP 1.9.2—LOSS OF PRESTRESS

1.10—DETAILS OF REINFORCEMENT 1.10.1—GENERAL 1.10.2—CONCRETE COVER

1.11—DEVELOPMENT OF PRESTRESSING REINFORCEMENT 1.11.1—DEVELOPMENT OF PRESTRESSING CFRP

1.12—DURABILITY 1.12.1—GENERAL 1.12.2—CONCRETE COVER 1.12.3—PROTECTION OF PRESTRESSING CFRP

1.13—PROVISIONS FOR STRUCTURE TYPES

1.14—REFERENCES

1.1—SCOPE AND LIMITATIONS

1.2—DEFINITIONS

1.3—NOTATIONS

1.4—MATERIAL PROPERTIES 1.4.1—PRESTRESSING CFRP 1.4.2—ANCHORAGES 1.4.3—DUCTS 1.4.4—HOLD-DOWN POINTS AND DEVIATORS

1.5—LIMIT STATES 1.5.1—SERVICE LIMIT STATE 1.5.2—FATIGUE LIMIT STATE 1.5.3—STRENGTH LIMIT STATE

1.6—DESIGN CONSIDERATIONS 1.6.1—GENERAL 1.6.2—EFFECT OF IMPOSED DEFORMATIONS 1.6.3—STRUT AND TIE MODEL

1.7—DESIGN FOR FLEXURAL AND AXIAL FORCE EFFECTS 1.7.1—ASSUMPTIONS FOR SERVICE AND FATIGUE LIMIT STATES 1.7.2—ASSUMPTIONS FOR STRENGTH LIMIT STATES 1.7.3—FLEXURAL MEMBERS

21


Commentary

for relevant

subtask

Commentary

for background

information

Articles of the

draft guide

specification

Structure of the draft guide specification

(AASHTO LRFD format)

22


Design Issues

Specification Specification

Article

Experimental

Subtask No

Stress Limit for

Prestressing CFRP

Straight

Tendons 1.5.0

1.9.1

6.1

6.6

At jacking 0.70ffrpu (pre/post)

At transfer 0.65ffrpu (pre/post)

Harped/

Draped 1.9.1

6.1

6.6

Stress increase due to harping,

ch

frp

hR

yE

Losses

Elastic

Shortening 1.9.2

6.3

6.4 cir

ci

pf

E

EES for pretensioned

Creep 1.9.2 6.4 cdscir

c

p

cr ffE

EKRHCR

201.077.037.1

Shrinkage 1.9.2 6.4

SH = 117- 1.05 RH, for

pretensioned

SH = 94 – 0.85 RH, for post-

tensioned

Relaxation 1.9.2 6.3 Δ𝑓𝑝𝑅1 = 0.23 + 0.345 log 𝑡

Friction

Losses 1.9.2 6.6

Px=Pj e-(+x)

Anchorage

Seating Loss 1.9.2 6.3

L

EP

frpAS

AS

Temperature

Effect 1.9.2 6.4

frpcfrpT ETP

23


Design Issues


Article

Experimental

Subtask No

Flexural Design

Resistance

Factors 1.5.3 6.8

= 0.85 (tension-controlled),

=0.65 (compression-controlled)

= 0.90 (shear)

Stress Strain

for CFRP

1.4.0

1.4.1

6.1

6.6

Linear

Serviceability

Limit States

Long Term

Deflection 1.7.3 6.5 Effective modular ratio 1.6 n.

Fatigue 1.5.2 6.6 No significant effect for uncracked

members.

Ductility /

Deformability Deformability 1.4.0 6.6

frps

frpu

ad

kdd

1 or

𝜇𝑒𝑛 = 0.5 𝐸𝑡𝑜𝑡

𝐸𝑒𝑙𝑎+ 1

24


Design Issues


Article

Experimental

Subtask No

Shear Design 1.8.1

1.8.2

6.6

6.7

vvccstcr dbfVVV 25.0

Bond, Development Length

and Transfer Length

1.11.0

1.11.1

6.5

6.6

Ld= Lt + Lfb where,Transfer length,

Lt

67.0

cit

tpi

tf

dfL

(in mm) for CFRP

Flexural bond length, Lfb

67.0

cf

tpefrpu

fbf

dffL

(in mm) for

CFRP

Unbonded Prestressing 1.7.3 6.6 frpu

u

p

cupupep fc

dEff 8.01

25

Outline of the Material Specification

(Section 2)

NCHRP 12-97 Project Program – MATERIAL SPECIFICATION

2.1—SCOPE 2.2—DEFINITIONS 2.3—NON-STANDARD DOCUMENTS 2.4—MATERIAL AND MANUFACTURE 2.5—PHYSICAL PROPERTIES 2.6—MECHANICAL PROPERTIES 2.7—DURABILITY PROPERTIES 2.8—OTHER REQUIREMENTS 2.9—SAMPLING 2.10—CERTIFICATION 2.11—MARKINGS 2.12—REFERENCES

A template of material specification for the prestressing CFRP systems is

developed.

• Follows a similar outline as the “AASHTO LRFD Bridge Design

Guide Specifications for GFRP-Reinforced Concrete Bridge

Decks and Traffic Railings”.

• Default values and limits provided within the material

specification are subject to change.

26

NCHRP 12-97 Project Program – MATERIAL SPECIFICATION

• The Research Team will revise and update the current provisions of

the Material Specification considering AASHTO MP 22-13 and

provide the background information of the provisions in commentary,

wherever necessary, as a part of Task 8.


Task 6

• Experimental Program

Task 7

• Revised Guide Specification

Task 8

• Design Examples and Template of Material Specification

Task 9

• Final Report

27

28

Task 6 : Experimental Program Subtask 6.1: Jacking stresses for depressed strands

Subtask 6.2:

Anchorage detailing recommendations and strength requirements

Subtask 6.3:

Strand relaxation and anchorage seating losses

Subtask 6.4:

Prestress losses due to thermal fluctuations, concrete creep, and shrinkage

Subtask 6.5: Measurement of transfer length, camber and long -term deflections

Subtask 6.6: Full-scale beam tests

Subtask 6.7:

Analysis and refinement of existing design models

Subtask 6.8: Reliability analysis and calibration of LRFD factors

Subtask 6.9:

Development of technical memorandum and panel meeting



29

Subtask 6.8 Reliability

Subtask 6.4 Losses

Subtask 6.2 Anchorages

Subtask 6.5 Transfer length,

camber, long-term

deflections

Subtask 6.9 Technical

Memorandum

Subtask 6.1 Jacking stresses

Material properties

Subtask 6.6 Full-scale beams

Subtask 6.7 Analytical methods

Subtask 6.3 Relaxation

The interdependency of experimental research subtasks

C

30

Subtask Testing variables – critical parameters

Expected outcome

Impacted articles of proposed guide

specification

Sub

task

6

.1

Jack

ing

stre

sse

s M

ate

rial

pro

pe

rtie

s Prestressing CFRP

system type Harping angle Hold-down device

dimensions Hold-down device

material

Material properties including load-strain response of prestressing CFRP systems

Jacking limits for depressed prestressing CFRP systems

Details of hold-down points and devices

1.4—MATERIAL PROPERTIES 1.4.1—Prestressing CFRP 1.4.1.1- General 1.4.1.2- Tensile Strength and Strain 1.4.1.3- Modulus of Elasticity 1.4.4—Hold-Down Points and Deviators 1.9—PRESTRESSING 1.9.1—Stress Limitations for Prestressing CFRP 1.9.1.1- Tendons with Angle Points or Curves

Sub

task

6

.2

An

cho

rage

s Anchorage

performances of various prestressing CFRP systems

Anchorage system strength

limitations

1.4—MATERIAL PROPERTIES 1.4.2—Anchorages

Sub

task

6

.3

Re

laxa

tio

n

Prestressing CFRP

system type Jacking stress level

Relaxation loss Anchorage seating loss

1.9—PRESTRESSING 1.9.2—Loss of Prestress 1.9.2.2- Instantaneous Losses 1.9.2.2.1- Anchorage Set 1.9.2.3- Approximate Estimate of Time-Dependent Losses 1.9.2.4- Refined Estimate of Time-Dependent Losses 1.9.2.4.2- Relaxation of Prestressing CFRP

NCHRP 12-97 PROJECT PROGRAM – Experimental Subtasks

31


Expected outcome


specification

Sub

task

6

.4

Lo

sse

s

Prestressing CFRP

system type Jacking stress level Transverse

reinforcement ratio Thermal fluctuations

Concrete creep & shrinkage

losses Losses due to thermal

fluctuations

1.9—PRESTRESSING 1.9.2—Loss of Prestress 1.9.2.1- Total Loss of Prestress 1.9.2.3- Approximate Estimate of Time-Dependent Losses 1.9.2.4- Refined Estimate of Time-Dependent Losses 1.9.2.5- Losses due to Temperature Changes

Sub

task

6

.5

Tran

sfe

r le

ngt

h, c

amb

er,

lon

g-te

rm

def

lect

ion

s

Full scale concrete beams pretensioned with bonded strands:

- Prestressing CFRP system type

- Tendon profile

Scaled prestressed concrete beams:

- Long term deflections

Camber Transfer length Short term deflection

Long term deflections

1.7—DESIGN FOR FLEXURAL AND AXIAL FORCE EFFECTS 1.7.3- Flexural Members 1.7.3.4- Deformations 1.7.3.4.1- General 1.7.3.4.2- Deflection and Camber 1.11—DEVELOPMENT OF PRESTRESSING REINFORCEMENT 1.11.1-Development of Prestressing CFRP 1.11.1.1- General 1.11.1.2- Bonded Prestressing CFRP


32


Expected outcome Impacted articles of proposed

guide specification Su

bta

sk

6.6

Fu

ll-sc

ale

be

ams

Prestressing CFRP system

Pre- or post- tensioning Bonded or unbonded

strands Tendon profile Monotonic or fatigue

loading

Flexural design model for prestressed concrete bridge beams including service, fatigue and strength limit states.

Prestress losses Specifications for ducts and

hold-down devices Deformations

1.4—MATERIAL PROPERTIES 1.4.2— Anchorages 1.4.3—Ducts 1.4.3.1-General 1.4.3.2-Size of Ducts 1.4.4—Hold-Down Points and Deviators 1.5—LIMIT STATES 1.5.1—Service Limit State 1.5.2—Fatigue Limit State 1.5.2.1-General 1.5.2.2-Prestressing Tendons 1.5.3—Strength Limit State 1.5.3.1-General 1.5.3.2-Resistance Factors 1.7—DESIGN FOR FLEXURAL AND AXIAL FORCE EFFECTS 1.7.3-Flexural Members 1.7.3.1-Stress in Prestressing CFRP at Nominal Flexural Resistance 1.7.3.2-Flexural Resistance 1.7.3.3-Limits for CFRP Reinforcement 1.7.3.4-Deformations 1.8—SHEAR 1.9—PRESTRESSING 1.9.1-Stress Limits for Prestressing CFRP 1.9.2-Loss of Prestress 1.10—DETAILS OF REINFORCEMENT 1.11—DEVELOPMENT OF PRESTRESSING REINFORCEMENT 1.11.1—Development of Prestressing Strand


33


Expected outcome


specification

Sub

task

6

.7

An

alyt

ical

met

ho

ds All major and minor

parameters of other experimental subtasks

Supplement and validate experimental results

Stresses in anchorage zones Minimum reinforcement

ratio requirements Verify proposed design

methods

All relevant articles

Sub

task

6

.8

Re

liab

ility

All major and minor

parameters of the experimental subtasks

Resistance factors

1.5.0—LIMIT STATES 1.5.3.2—Resistance Factors


34


• Cables with twisted wires (Cable A)

• Cables with straight wires (Cable B)

• Solid bars

The prestressing CFRP systems that will be used within the

experimental phase are:

Cables Bars

B A

Material properties of all prestressing CFRP (cables and bars) will be

identified and verified under subtask 6.1 of the experimental program.

Each individual batch of prestressing CFRP received from the

manufacturers will be subjected to the material testing.

35


Comparison of material properties of the prestressing CFRP

(based on #4 bar nominal diameter or equivalent provided by manufacturer)

C

Cable A

Bar A

Cable B

Bar B

Cross-sectional property

Available diameter 0.2 in. (single strand)

0.295 in. -1.57 in (multi-strand)

0.25 in. (#2) - 0.625 in. (#5)

0.161 in. -3.217 in

0.25 in. (#2) – 0.5 in.

(#4)

Resin Epoxy Vinyl Ester Epoxy N/A*

Fiber Volume Ratio 0.65 N/A* N/A* N/A*

Longitudinal tensile strength, ksi

218-363 220-275 245-268 300-325

Longitudinal modulus, ksi 18,420-24,220 17,400-20,880 24,700-27000 18,000

Maximum longitudinal strain, %

1.0-1.7 1.18-1.33 0.99 1.67-1.81

36

NCHRP 12-97 PROJECT PROGRAM – Material Properties

The material characterization tests will be conducted in accordance with

ASTM Standard: D7205/D7205M-11 and D3171. Following material properties

will be identified:

• Ultimate tensile strain and strength,

• Modulus of elasticity, and

• Stress-strain curve of the prestressing CFRP

• Fiber content

The material characterization tests will also be in line with the provisions

of Section 2 (Material Specification) of the Draft Guide Specification (i.e.,

number of specimens, length of specimens, loading protocols, etc.)

Material Level Testing (Subtask 6.1)

37

NCHRP 12-97 PROJECT PROGRAM – Material Properties



Test setup for evaluation of harped strands and hold-down devices

JACKING STRESSES FOR HARPED/DRAPED

STRANDS

38

Roller with smooth

surface

Strain gage on non-

contact side of strand


CFRP Type Hold-down

Material Hold-down Diameter

Harping Angle

CFRP bars

Plastic 1 in. 10o - 15o - 20o

2 in. 10o - 15o - 20o

Steel 1 in. 10o - 15o - 20o

2 in. 10o - 15o - 20o

CFRP cables

Plastic 1 in. 10o - 15o - 20o

2 in. 10o - 15o - 20o

Steel 1 in. 10o - 15o - 20o

2 in. 10o - 15o - 20o

39

Test matrix for evaluation of harped strands and hold-

down devices

Three repetitions of each test configuration will be conducted


STRANDS

The objective of these repetitions is not to form a statistically significant data sample; rather the aim is to

test the reliability and repeatability of the experiments

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Testing Protocol:

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Initial stage - Specimens will be loaded up to 30% of their expected

tensile capacity and will be unloaded to 10% loading level. The

strains will be measured while the strand is being bent around the

harping pin.

Second stage – Specimens will be loaded up to their failure

monotonically with a loading rate of 0.1 in./min. Tensile strength and

ultimate strain will be measured.


STRANDS


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CFRP bars and cables will be stressed within an HSS to measure

their anchorage seating and loss due to relaxation.

STRAND RELAXATION AND ANCHORAGE SEATING LOSSES

HSS reaction

frame Strand anchor

Load cell

Potentiometer

Base plate

10, 15 or 20 ft. Strain gages

Test setup for evaluation of relaxation for prestressing CFRP

and anchorage seating loss

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42

Proposed test matrix for evaluation of strand relaxation

and anchorage seating losses

Prestressing CFRP Type Jacking Stress Prestressing CFRP length

CFRP bars

0.5 fpu 15 ft.

0.6 fpu 10ft. - 15 ft. – 20 ft.

0.7 fpu 15 ft.

CFRP cable with straight wires

0.5 fpu 15 ft.

0.6 fpu 10ft. - 15 ft. – 20 ft.

0.7 fpu 15 ft.

CFRP cable with twisted wires

0.5 fpu 15 ft.

0.6 fpu 10ft. - 15 ft. – 20 ft.

0.7 fpu 15 ft.

Three repetitions of each test configuration will be conducted



1st Stage – The prestressing CFRP will be stressed and the

anchorage seating losses will be measured.

2nd Stage – Sustained strains will be applied to a specified level for

maximum duration allowed within the project ( approx.. 12 months)

and loss of prestress force due to relaxation will be monitored.

3rd Stage – After removing sustained strains, coupons from the

strands will be subject to tensile testing to evaluate the residual

strength.

Testing Protocol:

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PRESTRESS LOSSES DUE TO THERMAL FLUCTUATIONS,

CONCRETE CREEP AND SHRINKAGE

Test Specimen Details:

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• Concrete prisms (6x6 in.) will be prestressed with prestressing

CFRP.

10 ft.

Thermocouple Strain gage


46

The specimens will be tested soon after casting in a controlled environmental

chamber (-20oF to 180oF) to represent the service temperature ranges for prestressed

concrete structures throughout most of the US.



Test setup for evaluation of thermally-induced losses


CFRP Type Transverse Reinforcement

Jacking Stress

CFRP bars

No

0.5 fpu

0.6 fpu

0.7 fpu

Yes

0.5 fpu

0.6 fpu

0.7 fpu

CFRP cables

No

0.5 fpu

0.6 fpu

0.7 fpu

Yes

0.5 fpu

0.6 fpu

0.7 fpu

Proposed test matrix for evaluation of thermally-induced losses

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1st Stage – after casting and curing, the specimens will be

placed in the environmental chamber and will be subjected to

temperature fluctuations ranging from -20oF to 180oF.

2nd Stage – the prisms will be kept at regular environmental

conditions for maximum duration allowable within the project

(12 months) to monitor the time-dependent creep and

shrinkage-induced prestress losses.

3rd Stage – the prisms will be returned to the environmental

chamber and subjected to thermal fluctuations to evaluate the

thermally-induced losses in mature concrete structures which

have experienced significant creep and shrinkage

Testing Protocol:

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Test Specimens




Test Specimen Details:

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LONG-TERM DEFLECTION

12.0 ft.

Front view

Beam 1a

2.0 ft. 4.5 ft. 4.5 ft. ½ ft. ½ ft.

Beam 1b

Threaded rods Inverted beam

6’’ x 10’’

cross-section Roller

supports HSS

Test set-up for long-term deflection measurements of prestressed

concrete beams

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Beam Number Prestressing CFRP Type Sustained Loads (% of ultimate)

Jacking Stress

Beam 1a CFRP bar

60 0.6 fpu

Beam 1b

Beam 2a CFRP cable with straight wires Beam 2b

Beam 3a CFRP cable with twisted wires Beam 3b

Proposed test matrix for evaluation long-term deformation of

prestressed concrete beams

Regarding the long-term deflection, no creep rupture testing will be conducted


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Testing Protocol:

Initial stage - Reduced scale concrete beams will be cast and prestressed

as matching pairs with identical material properties. Load will be applied and

maintained by the help of thread rods at the beam ends. The long-term

deflection measurements will be carried out for maximum allowable project

duration (12 months).

Second stage – Specimens will be loaded up to their failure monotonically

with a loading rate of 0.1 in./min.


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concrete beams

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concrete beams

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Full-scale Beam Testing (Subtask 6.6)

FULL SCALE BEAM TESTS

General:

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There is a distinct lack of data on large-scale and full-scale

CFRP prestressed ‘I’ shaped bridge beams.

To supplement existing experimental data with testing of full-

scale bridge beams that are designed, detailed, and constructed using

the same materials, methods, and techniques that will be used in practice

is necessary.

To ensure flexural dominant behavior with selected dimensions,

ASHTO TYPE I Girders are going to be tested. C

39.5 ft.


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Twelve (12) AASHTO Type I Girders

with 8’’ typical deck will be tested

Cross-sectional

properties


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* A minimum amount of unstressed reinforcement will be provided if necessary.

** 25% of the prestressing CFRP will be used as debonded

Strand Type

Prestressing System Prestressing Type

Strand Profile Loading Type Repetition Beam ID

CFRP Cable

Cable with twisted wires

Pretension Straight Monotonic 2 CPrSM(#)


Flexural fatigue 1 CPrSF


Post-tension Draped Monotonic 2 CPoDM(#)

Cable with straight wires

Post-tension* (unbonded)

Straight Monotonic 1 CPouSM


Flexural fatigue 1 CPouSF


Draped Flexural fatigue 1 CPouDF

CFRP Bar

Solid bar Pretension Harped

Monotonic 1 BPrHM

Solid bar Flexural fatigue 2 BPrHF(#)

Solid bar Pretension (Partially

debonded)**

Straight Monotonic 1 BPrpSM

Proposed test matrix for full-scale beam testing



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The beams will be produced at a local precast plant.

Heldenfels Enterprises, Inc. (www.heldenfels.com) 5700 IH-35 South (Exit 199)

San Marcos, TX 78666

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175 m.

• PCI Certified Precast Concrete

Plant

• 175 miles distance

• A dedicated production bed for

project throughout the project

• Experience with FRP

prestressing

http://www.heldenfels.com/






Four point flexure bending will be conducted for

flexure and flexural fatigue loading.

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Detailing of pretensioned concrete beams with straight prestressing CFRP


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Detailing of pretensioned concrete beams with harped prestressing CFRP

Different types of instrumentation schemes will be utilized:

1. Conventional instruments (i.e. LVDTs, string pots, potentiometers, load cells etc.) for global response parameters,

2. Strain gages for local measurements,

3. Advanced measurement devices (i.e. non contact measurements with ARAMIS and KRYPTON)

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Instrumentation:




Instrumentation:


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Advanced non-contact measurement devices

Digital image correlation (DIC)

system known as ARAMIS.

3D measurement system

based on CCD cameras, Krypton K 600

Production of Full-Scale Beam

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Production of the beams:


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Testing of the beams:


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Project Deliverables

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Revised Guide Specification (Task 7)

• The results and technical findings will be documented as a technical

memorandum.

TECHNICAL MEMORANDUM AND REVISED GUIDE

SPECIFICATION

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• Revised guide specification in AASHTO LRFD format and

commentary will be prepared.

Eight (8) design examples will be produced covering the following aspects of design:

Bonded pretensioned flexural design with;

1. Harped strands

2. Straight strands in a single layer

3. Straight strands in multiple layers

Bonded post-tensioned flexural design with;

4. Harped strands


6. Straight strands in multiple layers

Unbonded post-tensioned flexural design with*;

7. Draped strands


* The unbonded post-tensioning examples will be applicable for both internal and external applications with

appropriate limitations since the unbonded prestressing CFRP behavior is very similar for both cases.

However, no anchorage detailing will be conducted for external post-tensioning.

Design Examples and Material Testing specification

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Design Examples (Task 8)

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Design Examples and Material Testing specification

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Format and level of detail similar to that shown in the PCI Precast

Prestressed Concrete Bridge Design Manual

Templates with user friendly software (e.g. Mathcad, Matlab, Excel, etc.)

will be prepared.

A final template for material specification focusing on prestressing

system as a whole (including the anchorages) will also be

developed.

Design Examples (Task 8)

All eight design examples will include, where appropriate, all of the

following design elements:

• Shear design

• Calculation of prestressing losses

• Serviceability (deflections and camber)

• Detailing (harping, transfer length, development length, end zone

specific design elements)

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Acknowledgments: Many thanks to the funding agency, my collaborators, University

of Houston staff, CFRP suppliers, and precast plant staff

National Cooperative Highway Research Program

http://www.trb.org/

THANK YOU FOR YOUR

ATTENTION

NCHRP 12-97

National Cooperative Highway Research Program

Courtesy of Dr. Kinga Vojnits

Abdeldjelil Belarbi, PhD, PE, FACI, FASCE

Distinguished Professor of Civil Engineering

[email protected]

mailto:[email protected]

Guide Specification for the Design of Concrete Bridge...

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