EVALUATION OF THE FRP-RETROFITTED ARCHES IN THE CASTLEWOOD CANYON BRIDGE ...

249 Pages·2005·9.89 MB·English

Report No. CDOT-DTD-R-2005-01
Final Report

EVALUATION OF THE FRP-RETROFITTED ARCHES IN THE
CASTLEWOOD CANYON BRIDGE

Delchi Fafach and Benson Shing
Sunyoung Chang and Yunping Xi

December 2004

COLORADO DEPARTMENT OF TRANSPORTATION
RESEARCH BRANCH
The contents of this report reflect the views of the
authors, who are responsible for the facts and
accuracy of the data presented herein. The contents
do not necessarily reflect the official views of the
Colorado Department of Transportation or the Federal
Highway Administration. This report does not
constitute a standard, specification, or regulation.

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Technical Report Documentation Page
1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.
CDOT-DTD-R-2005-01
4. Title and Subtitle 5. Report Date
EVALUATION OF THE FRP-RETROFITTED ARCHES IN THE December 2004
CASTLEWOOD CANYON BRIDGE 6. Performing Organization Code

7. Author(s) 8. Performing Organization Report No.
Delchi Fafach and Benson Shing; Sunyoung Chang, and Yunping Xi CDOT-DTD-R-2005-01
9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)
University of Colorado – Boulder
Campus Box 561 11. Contract or Grant No.
Boulder, CO 80309 87.50
12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered
Colorado Department of Transportation - Research
4201 E. Arkansas Ave.
14. Sponsoring Agency Code
Denver, CO 80222

15. Supplementary Notes
Prepared in cooperation with the U.S. Department of Transportation, Federal Highway Administration
16. Abstract
Fiber-reinforced composites are increasingly being used for repair of deteriorating and understrength concrete decks and columns due
to their excellent properties. Carbon fiber-reinforced polymers (CFRP) sheets were used in this project to strengthen the arch. Four
quarter-scale beams were tested to model the arch ribs before and after the retrofit to evaluate the strength of the arches. Two of the
beams were designed to model the behavior of an arch rib below a heavily loaded column. The remaining two beams were designed
to model the moment connection at the base of an arch. The test results were used to calibrate an analysis technique which was used
to predict the strength of the full-scale arches. The retrofitted test specimens were between 22% and 30% stronger in bending than the
control specimens. However, the strengthening scheme did not increase the strength of the retrofitted specimens as much as expected.
The externally bonded FRP ruptured earlier than expected in one test specimen. Another specimen experienced peeling of the
concrete which led to bond failure of the FRP rods.

Durability of bond between CFRP and concrete was studied by the pull-off bond strength test after various long-term conditioning,
including room temperature, wetting in water, wetting/drying in water, immersion in 3% NaCl, freeze-thaw, immersion in 0.2N
NaOH, and high temperature. The experimental results indicate that the bond strengths satisfy the selected acceptance criterion,
although the bond strengths were significantly affected by the long-term environmental exposures. However, the bond failure modes
were unsatisfactory based on the ACI criterion in that the ideal failure mode is to have 100% failure in substrate.

A wireless real-time remote bridge monitoring system was installed on the bridge site to evaluate the performance of the arch and the
effectiveness of the corrosion inhibitor applied in the arch rib. The maximum strain recorded was 1400 µε (0.14 %) under the service
conditions, which is about 23 % of the minimum ultimate rupture strain. The chloride content and the corrosion potential in the new
shotcrete cover have been increased, which are due to the re-distribution of the existing chloride in the old concrete.

Implementation:
The axial forces in the arches may limit the strength increase due to the longitudinal FRP. The transverse FRP increases both the
strength and the ductility of the arches. The effects of concrete peeling must be considered at the arch-foundation moment
connections, especially because of the CFRP dowel development at these locations.

The degradation in the pull-off strength must be considered in the specifications related to the structural design if the FRPs are to be
used for repair. The monitoring results obtained so far provide valuable information. The monitoring process of the arch in the
bridge should be continued, which will be very important for evaluating the effectiveness of carbon FRP repairing, the performance of
the corrosion inhibitor, and long-term performance of the strengthened arch ribs.
17. Keywords 18. Distribution Statement
durability, CFRPs, pull-off strength, structure No restrictions. This document is available to the public through the National
monitoring Technical Information Service, Springfield, VA 22161
19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price
Unclassified Unclassified 249
Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
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EVALUATION OF THE FRP-RETROFITTED ARCHES IN THE
CASTLEWOOD CANYON BRIDGE

by

Delchi Fafach and Benson Shing
Sunyoung Chang and Yunping Xi

University of Colorado at Boulder

Report No. CDOT-DTD-R-2005-01
Final Report

Prepared for
The Colorado Department of Transportation
Research Branch

December 2004

Colorado Department of Transportation
Research Branch
4201 E. Arkansas Ave.
Denver, CO 80222
[phone]
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Acknowledgements

This study was sponsored by the Federal Highway Administration (FHWA) and conducted in
conjunction with the Colorado Department of Transportation (CDOT) as part of FHWA’s
Innovative Bridge Research and Construction Program. The project was monitored by Matthew
Greer of the Colorado Division of FHWA and administered by Ahmad Ardani of the Research
Branch of CDOT.

Mike Mohseni and Trevor Wang of CDOT were the engineers for the Castlewood Canyon
Bridge. Their technical assistance with the design of the test specimens is gratefully
acknowledged.

The continued technical support of Pete Milligan of Fyfe Co., who designed the Fibrwrap plans
for the Castlewood Canyon Bridge, was very helpful. The writers also wish to thank Rick
Wheeler of Lafarge, who generously donated time and materials for the beam specimens.

The writers appreciate the invaluable assistance of Thomas L. Bowen, manager of the Structures
and Materials Testing Laboratory of the University of Colorado, and the laboratory assistants,
Chris Cloutier, David Shaw, Dan Caughlin, Chris Baksa, and Steve Cole in the experimental
work. The writers would also like to thank Professor Enrico Spacone for the use of his reinforced
concrete axial/bending analysis program and Research Associate Holger Basche for his
continuous help throughout the entire project, especially in the preparation of the report.

The writers would like to express their thanks to the Colorado DOT for continuous support and
encouragement throughout this study, and specifically to Ahmad Ardani and Richard Griffin of
CDOT Research Branch; Trever Wang, Ali Haraj, and Michael McMullen of CDOT Staff
Bridge; Greg Lowery of CDOT Staff Materials; and Matt Greer of FHWA for their valuable
suggestions and inputs. The writers would also like to express their thanks to Ms. Lindsay
Marshall for careful editing of the report.
Opinions expressed in this report are those of the writers and do not necessarily represent those
of CDOT or FHWA .
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Executive Summary

Under the Innovative Bridge Research and Construction (IBRC) program of the Federal
Highway Administration (FHWA), the Colorado Department of Transportation (CDOT) has
used a combination of carbon fiber-reinforced polymer (CFRP) bars and externally bonded
CFRP fabric to strengthen the arch bridge in Castlewood Canyon State Park. The original bridge
was in poor condition and required repair and strengthening to meet increased traffic loads due to
widened lanes. During the summer of 2003, the bridge arches were repaired and strengthened.
An innovative FRP scheme provides longitudinal reinforcement for flexural enhancement and
transverse reinforcement for confinement, shear enhancement, and protection against concrete
deterioration and steel corrosion.

The performance of FRP strengthening work was evaluated from several aspects. First, we
evaluated the strength of the arch ribs in the Castlewood Canyon Bridge. For this purpose, four
quarter-scale beams were tested to model the arch ribs before and after the retrofit. The test
results were used to calibrate a theoretical analysis model which was then used to evaluate the
strength of the arch ribs.

The retrofitted test specimens were between 22% and 30% stronger in bending than the control
specimens. However, the strengthening scheme did not increase the strength of the retrofitted
specimens as much as expected. The externally bonded FRP ruptured earlier than expected in
one test specimen. The other retrofitted specimen experienced peeling of the concrete which led
to bond failure of the FRP rods. This indicates that the bond between CFRP and substrate is a
critical factor in order to increase load carrying capacity of structures and effectiveness of
strengthening systems.

While the test specimens failed in tension, a load analysis of the arch ribs indicates that the arch
strengths are governed by crushing of the concrete in compression. The test results were used to
calibrate an analysis model that was in turn used to compute axial load-moment strength
interaction diagrams for the arch ribs. However, further tests could be conducted on similar
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specimens under varied axial load-bending moment ratios in order to investigate more points
along the strength interaction diagrams.

A long-term durability of bond strength between CFRP sheets and concrete/shotcrete under
various accelerated environment conditions was performed. The effect of corrosion inhibitor on
the bond strength was also evaluated. The bond strength was evaluated as a measure of pull-off
strength. Seven accelerated environmental parameters were utilized in this study: room
temperature, freeze-thaw cycles, wetting in water, wetting/drying cycles in water, deicing
chemicals, sodium hydroxide, and high temperature.

Pull-off strengths of CFRP sheet-to-concrete/shotcrete after being exposed to the environmental
parameters were satisfactory based on the selected acceptance criterion. Therefore, good
protection against aggressive environmental conditions can be provided by the CFRP wrapping
repair method. However, the bond failure modes were unsatisfactory based on the ACI criterion
in that the ideal failure mode is to have 100% failure in substrate.

In case of a fire, the bond strength may significantly decrease because the epoxy starts to
decompose at a temperature of 446 oF. For the application of CFRP sheets in concrete structures
the maximum useable temperature should be below 446 oF. Above that temperature, special
surface treatments or additives should be applied to the FRP sheets to enhance their fire
endurance.

In order to monitor the performance of the repaired bridge, a wireless remote structural
monitoring system was installed on the bridge. The strains in the surface of the arch and five
other corrosion related parameters were monitored using the wireless technology. The maximum
strain was recorded up to 1400 µε (0.14 %) under the service conditions. The overall variation of
the strain gages in the arch indicated that the temperature variation currently governs the internal
strain distribution of the arch. According to the design specification, the 0.14 % of the maximum
strain reached 23 % of the minimum ultimate rupture strain. An increase of the chloride content
was observed in the new shotcrete cover. It is not due to the penetration of chloride from outside
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of the cover; because the C-FRP wrapping and the shotcrete are brand new, it will take some
time for the chloride to penetrate into the concrete. The increase of the chloride concentration
may be due to the re-distribution of the internal chloride in existing concrete. Since the internal
chloride concentration of existing concrete is higher than that of the new shotcrete, the chloride
will diffuse from the existing concrete to the new shotcrete, which makes the chloride level
increase.
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Implementation Statement

The axial forces in the arches may limit the strength increase due to the longitudinal FRP. The
transverse FRP increases both the strength and the ductility of the arches. The effects of concrete
peeling must be considered at the arch-foundation moment connections, especially because of
the CFRP dowel development at these locations.

The degradation in the pull-off strength must be considered in the specifications related to the
structural design if the FRPs are to be used for repair. The monitoring results obtained so far
provide valuable information. The monitoring process of the arch in the bridge should be
continued, which will be very important for evaluating the effectiveness of carbon FRP repairing,
the performance of the corrosion inhibitor, and long-term performance of the strengthened arch
ribs.

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Table of Contents

CHAPTER 1. STRENGTH EVALUATION OF THE ARCH RIBS.............................1
1.1 Introduction..................................................................................................................1
1.1.1 Background............................................................................................................1
1.2.1 Two examples of FRPs in bridge strengthening and repair...................................2
1.3.1 Project overview....................................................................................................4
1.4.1 Objectives and scope.............................................................................................5
1.5.1 Organization of Chapter 1.....................................................................................5
1.2 Bridge Overview..........................................................................................................8
1.2.1 Original design......................................................................................................8
1.2.2 Repair and strengthening.....................................................................................10
1.2.3 Materials..............................................................................................................15
1.3 Strength Analysis of Rectangular Reinforced Concrete Sections with FRP..............16
1.3.1 Fundamental assumptions...................................................................................16
1.3.2 Concrete material behavior..................................................................................16
1.3.3 Summary of concrete constitutive models and their application to beam-column
analysis.........................................................................................................................25
1.3.4 Other material behaviors.....................................................................................28
1.3.5 Moment-curvature relationships for members under combined bending and axial
load...............................................................................................................................28
1.4 Specimen Design and Analysis..................................................................................32
1.4.1 Bridge analysis....................................................................................................32
1.4.2 Specimen designs................................................................................................37
1.4.3 Specimen analysis...............................................................................................45
1.5 Experimental Program................................................................................................49
1.5.1 Specimen fabrication...........................................................................................49
1.5.2 Material properties...............................................................................................54
1.5.3 Test setup.............................................................................................................56
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