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
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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
NCHRP 12-97 Program – Phase I
Overview
Synthesis of Practice 9
NCHRP 12-97 Program – Phase I
Experimental Database
A total number of 258 beams were compiled within the database and classified under categories shown above
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
NCHRP 12-97 Program – Phase I
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
NCHRP 12-97 Program – Phase I
Comparison with existing guidelines
- Same - has provision for - doesn’t have provision for
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
NCHRP 12-97 Program – Phase I
Evaluation of Collected Information
Comparison with existing guidelines
- Same - has provision for - doesn’t have provision for
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
NCHRP 12-97 Project Program – GUIDE SPECIFICATION
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
NCHRP 12-97 Project Program – GUIDE SPECIFICATION
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
NCHRP 12-97 Project Program – GUIDE SPECIFICATION
Commentary
for relevant
subtask
Commentary
for background
information
Articles of the
draft guide
specification
Structure of the draft guide specification
(AASHTO LRFD format)
22
NCHRP 12-97 Project Program – GUIDE SPECIFICATION
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
NCHRP 12-97 Project Program – GUIDE SPECIFICATION
Design Issues
Specification Specification
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
NCHRP 12-97 Project Program – GUIDE SPECIFICATION
Design Issues
Specification Specification
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
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.
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
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
NCHRP 12-97 Project Program – Phase II
NCHRP 12-97 Project Program – Phase II
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
Subtask Testing variables – critical parameters
Expected outcome
Impacted articles of proposed guide
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
NCHRP 12-97 PROJECT PROGRAM – Experimental Subtasks
32
Subtask Testing variables – critical parameters
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
NCHRP 12-97 PROJECT PROGRAM – Experimental Subtasks
33
Subtask Testing variables – critical parameters
Expected outcome
Impacted articles of proposed guide
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
NCHRP 12-97 PROJECT PROGRAM – Experimental Subtasks
34
NCHRP 12-97 PROJECT PROGRAM – Prestressing CFRP
• 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
NCHRP 12-97 PROJECT PROGRAM – Prestressing CFRP
Comparison of material properties of the prestressing CFRP
(based on #4 bar nominal diameter or equivalent provided by manufacturer)