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University of Toledo University of Cincinnati
October 26 OTEC 2016 Columbus, OH
Structural Analysis & Field Testing
of a CFRP Wrapped Pier Cap
Dr. Serhan Guner
Dr. Douglas Nims
Mr. John Morganstern
Dr. Victor Hunt
Dr. Arthur Helmicki
Mr. Mahdi Norouzi
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
2
Outline
Problem Statement
Objectives
Structural Analysis
Field Testing
Preliminary Findings
3
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• I-71 SB Interchange at Fort Hayes.
• Designed in 1961 for three lanes of traffic.
Problem Statement
Original 3 lanes
Original Pier Cap
4
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• In 2011, two more lanes & a new pier cap added.
• Live load on the original pier cap increased.
Shear & flexure overloads.
Problem Statement
New Pier Cap
Original 3 lanes
New 2 lanes
Original Pier Cap
(Focus of this study)
5
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• ODOT retrofitted the cap with CFRP composites
Problem Statement
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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• Retrofit design was done based on ACI 440, which contains many assumptions.
• Actual contribution of the CFRP to the load carrying capacity is unknown.
• ODOT wanted scientific evidence on the contribution of CFRP.
Does CFRP wrap indeed work?
Problem Statement
7
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• Understand the behaviour of the cap before and after the retrofit.• Use structural analysis.
• Measure CFRP strains & validate analysis results.
• Develop a controlled truck testing procedure.
• Consider ambient traffic, daily thermal changes, and
truck loading.
• Understand CFRP contributions to response.
• Provide recommendations for future retrofits.--
Objectives
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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• Bridge FRA-071-1835L at Forth Hayes Interchange
• Original Construction as per 1961 specifications
Bridge Background
9
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
Bridge Background
• North and South piers make up a 3 span bridge
• Both stepped between bearings, supported by 3 circular columns
• North pier is the focus of this study.
10
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
Bridge Background
• Total length of the cap ≈ 55 ft (16.8 m)
11
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• 7 bearing pads, equally spaced.
• Section depth ≈ 4’-3” (1300 mm)
Bridge Background
12
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• Entire cap is a disturbed region & deep beam.
Bridge Background
13
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• Light amounts of shear reinforcement.
• No skin reinforcement.
Bridge Background
14
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• Section is designed for negative flexure.
Bridge Background
15
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• New pier was built.
• Bridge deck was widened.
• Traffic was shifted to the new pier cap.
• Existing cap was wrapped while no live traffic load.
CFRP Retrofit Procedure
New Pier Cap Existing Pier Cap
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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CFRP Retrofit Procedure
Epoxy applied then
CFRP wrapped over
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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CFRP Retrofit (Shear)
Primary Fiber Directions
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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CFRP Retrofit (Flexure)
Primary Fiber Directions
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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CFRP Retrofit Procedure
SikaWrap Cured Laminate
• Thickness = 0.02” (0.5 mm)
• Tensile strength = 105 ksi (725 MPa)
• Mod. of Elast. = 8,200 ksi (56,500 MPa)
• Elongation at break = 1.0 % (10 me)Shear
Strengthening
Flexure
Strengthening
Flexure
Strengthening
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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• Understand the linear strain field.
• Assess contributions of CFRP composite.
• Locate high strain locations for field testing.
--
Linear-Elastic Analysis
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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• Load analysis is performed in 2011.
• Two critical load cases:
• Load Case #12: trucks in two west southbound lanes
• Load Case #16: trucks in central southbound lane
Loading
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Load Case #12Truck locationTruck location
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Load Case #16Truck location
24
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
Un-Retrofitted Model (Dead Load Only)
Linear-Elastic Analysis
123 kips each550 kN
Z
X
N
Shell Element• Ec = 3,800 ksi (26,200 MPa)• f’c = 4.0 ksi (27.6 MPa)• Possion’s Ratio = 0.2• Mesh aspect ratio = 1.0 approx.
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Displacements and Principal Stresses
Z
X
Δ = 0.065” (1.65 mm)
Δ = 0.0047” (0.12 mm)
Tens. (+) psi
Comp. (-) psi
N
Max Tensile Stress = 0.65 ksi (4.5 MPa) Strain = 171 μe
Max Compressive Stress = 1.68 ksi (11.6 MPa) Strain = 442 μe
26
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• Un-Retrofitted Model (Load Case #12)
Linear-Elastic Analysis
Z
X
N
168 kips 183 189 183 133 124 123750 kN 815 840 815 590 550 550
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Displacements and Principal Stresses
Z
X
Tens. (+) psi
Comp. (-) psi
N
Δ = 0.08” (0.20 mm)
Δ = 0.088” (2.25 mm)
Max Tensile Stress = 0.9 ksi (6.2 MPa) Strain = 237 μe
Max Compressive Stress = 2.27 ksi (15.7 MPa) Strain = 597 μe
28
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• Un-Retrofitted Model (Load Case #16)
Linear-Elastic Analysis
123 kips 163 196 183 128 124 123550 kN 725 875 815 570 550 550
Z
X
N
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Displacements and Principal Stresses
Z
X
Tens. (+) psi
Comp. (-) psi
N
Δ = 0.061” (1.55 mm)
Δ = 0.011” (0.28 mm) Δ = 0.064” (1.63 mm)
Max Tensile Stress = 0.676 ksi (4.6 MPa) Strain = 178 μe
Max Compressive Stress = 1.64 ksi (11.3 MPa) Strain = 432 μe
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Result Comparisons
Results
• Max stress locations do not change.
• Pier to cap connection should be instrumented for field testing.
Max Tip Disp. (in)
Max Stresses (ksi)Location of Max
Stresses Max strains
(micro-strain)
Tensile Comp. Tensile Comp. Tensile Comp.
DL only 0.065 0.65 1.68Top of
BearingBot of
Bearing171 442
Case # 12 (LL+DL)
0.088 0.90 2.26Top of
BearingBot of
Bearing237 597
Case # 16 (LL+DL)
0.064 0.68 1.64Top of
BearingBot of
Bearing178 432
31
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
Retrofitted Model (Dead Load Only)
Linear-Elastic Analysis
123 kips each550 kN
Z
X
N
Orthotropic CFRP Shell ElementHex 117C for Shear
• Ez = 8,200 ksi (56,500 MPa)• Gxz=2733 ksi• Gxz=0.5
Hex 230C for Flexure• Ex = 8,200 ksi (56,500 MPa)• Gxy=2952 ksi• Gxy=0.5
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Displacements and Principal Stresses
Z
X
Δ = 0.065” (1.65 mm)
Δ = 0.0047” (0.12 mm)
Tens. (+) psi
Comp. (-) psi
N
Max Tensile Stress = 0.85 ksi (5.9 MPa) in CFRP Strain = 96 μe
Max Compressive Stress = 1.68 ksi (11.6 MPa) in concreteStrain = 442 μe
33
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• Retrofitted Model (Load Case #12)
Linear-Elastic Analysis
Z
X
N
168 kips 183 189 183 133 124 123750 kN 815 840 815 590 550 550
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Displacements and Principal Stresses
Z
X
Tens. (+) psi
Comp. (-) psi
N
Δ = 0.08” (0.20 mm)
Δ = 0.088” (2.25 mm)
Max Tensile Stress = 1.14 ksi (7.9 MPa) Strain = 129 μe
Max Compressive Stress = 2.25 ksi (15.5 MPa) Strain = 592 μe
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Result Comparisons
Results
• Max stress locations do not change.
• Pier to cap connection should be instrumented for field testing.
Max Tip Disp. (in)
Max Stresses (ksi)Location of Max
Stresses Max strains
(micro-strain)
Tensile Comp. Tensile Comp. Tensile Comp.
DL only 0.065 0.85 1.68Top of
BearingBot of
Bearing96 442
Case # 12 (LL+DL)
0.088 1.14 2.25Top of
BearingBot of
Bearing129 592
36
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• Understand nonlinear bridge response
• Determine stress/strain conditions for service loads
• Confirm the governing behaviour and failure mode
--
Nonlinear Pushover Analysis
37
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• Create the finite element model.
• Increase loading monotonically with fixed proportions until structure fails.
• Obtain the load-deflection response.
What is Nonlinear Pushover Analysis?
Load Stage
Applied
Load
Deflection
Applied
Load
Capacity
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Is it permitted in AASHTO?
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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• VecTor2 used in this study.
• Developed at the University of Toronto, Canada.
• Based on the Modified Compression Field Theory(Vecchio and Collins,1986).
• Adopted by AASHTO LRFD.
• Verified with hundreds of large-scale experimental specimens.
• Considers shear and advanced concretebehaviours.
What tool to use?
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Concrete Hysteresis
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Reinforcement Hysteresis
Seckin (1981) Model
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Concrete Tension Stiffening
Modified Bentz (2005)
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Concrete Tension Softening
• Especially important for members:
• with no transverse reinforcement
• with no longitudinal reinforcement
• for plain concrete
fc1 = max (fc11 ;fc1
2)
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Concrete Variable Crack Spacing
• Crack spacing required by MCFT and DSFM for crack width calculation, crack check and crack slip.
• Variable crack spacing for each concrete layer
• for both smx and smy
• as per Collins and Mitchell (2001)
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Local Crack Calculations
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Out-of-Plane Confinement
• Taken into account as concrete elastic strain offset
• Based on Kupfer et al. (1969)
Case 1
Case 2
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Reinforcement Dowel Action
• Included into the global frame analysis
• Dowel Stiffness based on He and Kwan (2001)
• Average shear strains are used.
• Resisting moment is into fixed end forces.
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Reinforcement Buckling
Intermediate point
Two different stiffnesses
RDM Model (Akkaya, Guner and Vecchio, 2016)
49
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
Model Details
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Mesh and Loading
51
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
Material Modeling
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Load Stages 8 & 9
Load Stage 8:
(80% of Serv. Load)
No Cracking
Load Stage 9:
First Cracking
0.01 in (0.34 mm)
53
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
Load Stage 10 (Service Loads)
Load Stage 10:
Max Crack Width =
0.05 in (1.3 mm)
Wrapped
WrappedUnwrapped
54
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
Reinforcement Stresses
Load Stage 10:
Max rebar stress =
11.1 ksi (77 Mpa)
30% of yield
Min rebar stress =
-9.3 ksi (-63.9 Mpa)
55
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• Deflections
Displacements
Load Stage 10:
Max displacement =
0.15 in. (3.7 mm)
Criteria =
Span/300 = 0.35 in.
(8.8 mm)
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Concrete Principal Tensile Strains
Load Stage 10:
Max tensile strain =
1.44 x 10-3 in./in.
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Concrete Principal Compressive Strains
Load Stage 10:
Max comp. strain =
-0.69 x 10-3 in./in.
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Load Stage 25 (Failure Conditions)
Load Stage 25:
Failure Mode= Ductile
Shear-Flexure
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Reinforcement Stresses
Load Stage 25:
Max rebar stress =
40 ksi (275 MPa)
100% of yield
Min rebar stress =
- 40 ksi (-275 Mpa)
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CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• Verified the service load conditions.
• Crack pattern matches with actual conditions.
• Verified concrete and rebar stresses.
• Verified that the cap fails in a combined flexural-shear mode.
--
Nonlinear Analysis Results
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
61
Field Test #1 for Ambient Traffic (June 2016)
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Gauge Locations
BDI Rosette (#3002)
5 sets of 3 vibrating wire gauges on top fiber
2 BDI gauges on bottom fiber
2 BDI gauges on bottom fiber
1 BDI gauge on concrete (#2989)
2 BDI gages on top concrete(#2987)
Plan
Elev.
Analysis of Frames under Blast Loads S. Guner
63
Gauge Installation
West Cantilever under gore area
Analysis of Frames under Blast Loads S. Guner
64
Gauge Installation
65
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• BDI gauge rosette in compression zone on CFRP
Gauge Installation
Clear Lexan
Template
66
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• 1 BDI gauge at bottom of pier cap at west midspan
Gauge Installation
Plan
67
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
• Vibrating Wire Strain Gauge on top CFRP
Gauge Installation
Geokon Model 4000
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Test Results (BDI Gauges)
BDI #3002
BDI #2989
BDI #2987
7 μe for ambient traffic
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
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Test Results (Vibrating Wire Gauges)
50μe drift for Superglue over one month
No drift for epoxies: Sika 3001 & 3M DP460
-50
-30
-10
10
30
50
70
90
110
Stra
in (μ
e)
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
70
1. Pier cap safety is confirmed by structural analysis.
2. Service cracking pattern is captured by analysis.
3. Governing response is confirmed as flexure-shear.
4. Ambient traffic field testing confirmed that the CFRP picks up strain.
5. Analysis showed that CFRP does not significantly contribute to stiffness and response under ambient traffic.
6. Stage #2 testing data analysis is underway.
Preliminary Conclusions
University of Toledo University of Cincinnati
October 26 OTEC 2016 Columbus, OH
Questions & Comments?
Structural Analysis & Field Testing of
a CFRP Wrapped Pier Cap
Serhan Guner
Douglas Nims
John Morganstern
Victor Hunt
Arthur Helmicki
Mahdi Norouzi
CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt
72