high performance fiber reinforced concrete composites for bridge columns

High Performance Fiber Reinforced Concrete Composites for Bridge Columns

C.P. Ostertag and S.L. BillingtonUniversity of California, Berkeley and Stanford University

Quake Summit MeetingOctober 9, 2010

Civil and Environmental Engineering Departments

University of California, Berkeley Stanford University

Outline

• Motivation & Objective of Research

• Overview of Composite Materials Being Studied

• Experimental Program– Compression and Confinement Experiments

– Tension-Stiffening Experiments

• Future Work

• Conclusions

Motivation for ResearchDuctile fiber-reinforced composites are being studied in bridge pier designs

Models are needed to predict structural-scale performance

ECC

Self-Compacted

HyFRC

Self-compactedHyFRC column

v=0.37%

Conv. reinforced concrete column

v=0.70%

Self-compacted HyFRC column at 11.3% drift

-3 -2 -1 0 1 2 3 -30

-15

0

15

30

Late

ral F

orce

, (k

ips)

Drift Ratio,(%)

-4 -2 0 2 4

(a)

Test Specimen 1Terzic - Base45x - direction

-3 -2 -1 0 1 2 3 -30

-15

0

15

30

Drift Ratio,(%)

-4 -2 0 2 4

(b)

Test Specimen 1Terzic - Base45y - direction

-3 -2 -1 0 1 2 3 -30

-15

0

15

30

Lateral Displacement, (in.)

Late

ral F

orce

, (k

ips)

-4 -2 0 2 4

(c)

Test Specimen 2Terzic - Base45x - direction

-3 -2 -1 0 1 2 3 -30

-15

0

15

30

Lateral Displacement, (in.)

-4 -2 0 2 4

(d)

Test Specimen 2Terzic - Base45y - direction

Motivation for ResearchDamage reduction & enhanced performance with lower transverse reinf.

PEER (Ostertag & Panagiotou)

Motivation for ResearchHigher strength and ductility observed in reinforced HPFRCs

Kesner & Billington, 2004

ObjectiveTo conduct fundamental, small-scale experiments

on unreinforced and reinforced HPFRC materials to

develop analytical models and design guidelines for

application to bridge pier designs.

1. By how much can transverse reinforcement be reduced?

2. How much additional strain capacity does HPFRC have when reinforced?

Additional Questions:

Materials Being StudiedHigh Performance Fiber-Reinforced Composites

Tension Hardening

Deflection softening Deflection hardening

High Performance if it achieves hardening with less than 2% fiber volume

Materials Being StudiedHigh Performance Fiber-Reinforced Composites

0.0

0.5

1.0

1.5

2.0

2.5

0.00 0.01 0.02 0.03 0.04

Tensile Strain

Ten

sile

Str

ess

(MP

a)

ECC

Mortar

FRC

0.0

0.5

1.0

1.5

2.0

2.5

0.00 0.01 0.02 0.03 0.04

Tensile Strain

Ten

sile

Str

ess

(MP

a)

ECC

Mortar

FRC

10 mm

Less than 2% by volume of (PVA) fibers

Materials Being StudiedHigh Performance Fiber-Reinforced Composites

HyFRC (1.5% fiber volume)Can be self-compacting

Experimental ProgramCompression testing of confined HyFRC and ECC

Strain

Stress (MPa)-80

-70

-60

-50

-40

-30

-20

-10

10

-0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 0.02

?

PI: Claudia Ostertag

Compression ExperimentsThree levels of confinement

1” 2”3”

Five mix designs: Plain concrete and HyFRC, Plain SCC and SC-HyFRC, and ECC

v = 0.95% v = 0.48% v = 0.32%

• #3 bars longitudinally• 10-Gage wire (0.13mm) spirals

Compression ExperimentsSpecimens and measurements

• Unconfined 6”x 12” cylinders

• Confined 6”x12” cylinders • Strain via 2 LVDTS within 8 inch section• Equipment limited to displacements < 0.4”

• Confined 6”x12” cylinders w/ strain gages• Strain gages installed on spiral reinforcement• Strain averaged over entire height using 2 LVDTs• Equipment enabled strain calculations at large

displacements (~ 1”)

Compression ExperimentsHyFRC compared with conventional concrete

Strain

Control (conventional) concrete

HyFRC

0 0.002 0.004 0.008 0.01 0.0120.0060

2

5

7

Str

ess

(ksi

)

4

6

1

3

HyFRC has stable, extended softening behavior on its own

Compression ExperimentsHigh confinement ratio not needed with SC-HyFRC

SCC (1.91%)

v = 0.95% v = 0.32%v = 0.49%

1” 2” 3”

Compression ExperimentsConfined HyFRC Results (2” spacing)

Plain

HyFRC

SC-HyFRC

Delay in damage initiation and damage progression

Extensive spalling

Compression ExperimentsNo damage localization in SC-HyFRC

v =0.95%

SC-HyFRCPlain SCC

v =1.91%

v =0.95%

v =0.95%

Experimental ProgramTension stiffening in ECC & HyFRC

Tension stiffening

Bar in ECC

Bare bar

Bar in Concrete

Fischer & Li, 2002

No recording beyond 0.5% strain

Blunt & Ostertag, 2009

No uniaxial tension data

Tension-stiffening experimentsQuestions

1. What is the tension stiffening effect with HyFRC?

2. How does the HyFRC and ECC perform at large strains when reinforced?

3. Can basic material properties and geometry be used to predict the tension stiffening and reinforced response?

4. How does rebar size and volume of surrounding material impact tension stiffening?

Dogbones

Prisms

34”

Tension Stiffening ExperimentsTwo specimen designs evaluated

Tension Stiffening ExperimentsSpecimen Variables

2 geometries: prism & dogbone

3 mix designs: ECC, HyFRC, SC-HyFRC

2 reinforcing ratios: 1.25% and 1.9%

Plain specimens: (no reinforcing bar)

Material characterization tests (cylinders, beams, plates)

6”

Stress concentration factor of 1.16

Dogbone specimen designed

Inserts and grips machined

Tension Stiffening ExperimentsSpecimen design and set-up validation

Dogbones - Typical Failures

ECC3-4-1

ECC3-4-2 SC-HyFRC-4-2HyFRC-4-2

SC-HyFRC-4-1HyFRC-4-1

Rebar fyAs + ECC stress block

Tension Stiffening ExperimentsECC Dogbones – Preliminary Data

Average strength of plain HyFRC dogbones ~3-4 kips

Tension Stiffening ExperimentsHyFRC and SC-HyFRC Dogbones

• Develop modeling approaches with experimental data (additional tension/compression experiments needed)

• Validate modeling on new reinforced beam and column tests, and recent and upcoming bridge pier experiments

• Longer-term: Bond/pull-out testing for bond-slip characterization

Future WorkExperiments and Model Development

Plate Beam

ECCECC

Material Characterization for ModelingCan simple material testing be used to predict performance in reinforced components?

12”

PlatePlate Inverse analysis of flexural response

to estimate uniaxial tensile data

ECCECC

Material Characterization for ModelingCan simple material testing be used to predict performance in reinforced components?

Conclusions

1. Lower transverse steel ratios are possible with SC-HyFRC

2. No damage localization in compression with SC-HyFRC

3. Large-scale tensile dogbones loaded in curve of dogbone provide robust results

4. In tension, reinforced HPFRC materials can reach higher strains before forming a dominant failure crack than when they are unreinforced

Acknowledgements

Pacific Earthquake Engineering Research Center

Graduate Researchers Gabe Jen, Will Trono & Daniel Moreno

Headed Reinforcement Corporation