Structural Analysis & Field Testing of a CFRP Wrapped Pier Cap Presentations/Wednesday/73... · 7 CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt • Understand the behaviour of

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

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Outline

Problem Statement

Objectives

Structural Analysis

Field Testing

Preliminary Findings

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• I-71 SB Interchange at Fort Hayes.

• Designed in 1961 for three lanes of traffic.

Problem Statement

Original 3 lanes

Original Pier Cap

4


• 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)

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• ODOT retrofitted the cap with CFRP composites

Problem Statement


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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

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• 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


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• Bridge FRA-071-1835L at Forth Hayes Interchange

• Original Construction as per 1961 specifications

Bridge Background

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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.

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Bridge Background

• Total length of the cap ≈ 55 ft (16.8 m)

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• 7 bearing pads, equally spaced.

• Section depth ≈ 4’-3” (1300 mm)

Bridge Background

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• Entire cap is a disturbed region & deep beam.

Bridge Background

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• Light amounts of shear reinforcement.

• No skin reinforcement.

Bridge Background

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• Section is designed for negative flexure.

Bridge Background

15


• 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


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Epoxy applied then

CFRP wrapped over


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CFRP Retrofit (Shear)

Primary Fiber Directions


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CFRP Retrofit (Flexure)

Primary Fiber Directions


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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


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• Understand the linear strain field.

• Assess contributions of CFRP composite.

• Locate high strain locations for field testing.

--

Linear-Elastic Analysis


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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


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Load Case #12Truck locationTruck location


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Load Case #16Truck location

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Un-Retrofitted Model (Dead Load Only)


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.


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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

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• Un-Retrofitted Model (Load Case #12)


Z

X

N

168 kips 183 189 183 133 124 123750 kN 815 840 815 590 550 550


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Z

X

Tens. (+) psi

Comp. (-) psi

N

Δ = 0.08” (0.20 mm)

Δ = 0.088” (2.25 mm)



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• Un-Retrofitted Model (Load Case #16)


123 kips 163 196 183 128 124 123550 kN 725 875 815 570 550 550

Z

X

N


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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)




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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

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Retrofitted Model (Dead Load Only)


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


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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

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• Retrofitted Model (Load Case #12)


Z

X

N

168 kips 183 189 183 133 124 123750 kN 815 840 815 590 550 550


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Z

X

Tens. (+) psi

Comp. (-) psi

N

Δ = 0.08” (0.20 mm)

Δ = 0.088” (2.25 mm)




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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

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• Understand nonlinear bridge response

• Determine stress/strain conditions for service loads

• Confirm the governing behaviour and failure mode

--

Nonlinear Pushover Analysis

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• 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


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Is it permitted in AASHTO?


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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?


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Concrete Hysteresis


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Reinforcement Hysteresis

Seckin (1981) Model


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Concrete Tension Stiffening

Modified Bentz (2005)


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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)


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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)


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Local Crack Calculations


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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


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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.


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Reinforcement Buckling

Intermediate point

Two different stiffnesses

RDM Model (Akkaya, Guner and Vecchio, 2016)

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Model Details


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Mesh and Loading

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Material Modeling


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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)

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Load Stage 10 (Service Loads)

Load Stage 10:

Max Crack Width =

0.05 in (1.3 mm)

Wrapped

WrappedUnwrapped

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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)

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• Deflections

Displacements

Load Stage 10:

Max displacement =

0.15 in. (3.7 mm)

Criteria =

Span/300 = 0.35 in.

(8.8 mm)


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Concrete Principal Tensile Strains

Load Stage 10:

Max tensile strain =

1.44 x 10-3 in./in.


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Concrete Principal Compressive Strains

Load Stage 10:

Max comp. strain =

-0.69 x 10-3 in./in.


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Load Stage 25 (Failure Conditions)

Load Stage 25:

Failure Mode= Ductile

Shear-Flexure


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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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• 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


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Field Test #1 for Ambient Traffic (June 2016)


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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

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Gauge Installation

West Cantilever under gore area

Analysis of Frames under Blast Loads S. Guner

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Gauge Installation

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• BDI gauge rosette in compression zone on CFRP

Gauge Installation

Clear Lexan

Template

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• 1 BDI gauge at bottom of pier cap at west midspan

Gauge Installation

Plan

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• Vibrating Wire Strain Gauge on top CFRP

Gauge Installation

Geokon Model 4000


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Test Results (BDI Gauges)

BDI #3002

BDI #2989

BDI #2987

7 μe for ambient traffic


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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)


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


72

Documents

Structural Analysis & Field Testing of a CFRP Wrapped Pier Cap Presentations/Wednesday/73... · 7 CFRP Wrapped Pier Cap Testing S. Guner & V. Hunt • Understand the behaviour of