High Performance Fiber Reinforced Concrete Composites for Bridge Columns

High Performance Fiber Reinforced Concrete
Composites for Bridge Columns


C.P. Ostertag and S.L. Billington

University of California, Berkeley and Stanford University


Quake Summit Meeting

October 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 Research

Ductile fiber
-
reinforced composites are being studied in bridge pier designs



Models are needed to predict structural
-
scale performance

ECC

Self
-
Compacted
HyFRC

Self
-
compacted

HyFRC column

r
v
=0.37%

Conv. reinforced

concrete column

r
v
=0.70%

Self
-
compacted HyFRC column at 11.3% drift

-3
-2
-1
0
1
2
3
-30
-15
0
15
30
Lateral Force, (kips)
Drift Ratio,(%)


-4
-2
0
2
4
(a)
Test Specimen 1
Terzic - Base45
x - direction
-3
-2
-1
0
1
2
3
-30
-15
0
15
30
Drift Ratio,(%)


-4
-2
0
2
4
(b)
Test Specimen 1
Terzic - Base45
y - direction
-3
-2
-1
0
1
2
3
-30
-15
0
15
30
Lateral Displacement, (in.)
Lateral Force, (kips)


-4
-2
0
2
4
(c)
Test Specimen 2
Terzic - Base45
x - direction
-3
-2
-1
0
1
2
3
-30
-15
0
15
30
Lateral Displacement, (in.)


-4
-2
0
2
4
(d)
Test Specimen 2
Terzic - Base45
y - direction
Motivation for Research

Damage reduction & enhanced performance with lower transverse
reinf
.

PEER (Ostertag & Panagiotou)

Motivation for Research

Higher strength and ductility observed in reinforced HPFRCs

Kesner & Billington, 2004

Objective

To 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 Studied

High Performance Fiber
-
Reinforced Composites

Tension Hardening

Deflection softening

Deflection hardening

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

Materials Being Studied

High 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
Tensile Stress (MPa)
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
Tensile Stress (MPa)
ECC
Mortar
FRC
10 mm

Less than 2% by
volume of (PVA) fibers

Materials Being Studied

High Performance Fiber
-
Reinforced Composites

HyFRC (1.5% fiber volume)

Can be self
-
compacting

Experimental Program

Compression 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 Experiments

Three levels of confinement

1”

2”

3”

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

r
v

= 0.95%

r
v

= 0.48%

r
v

= 0.32%

•

#3 bars longitudinally

•

10
-
Gage wire (0.13mm) spirals

Compression Experiments

Specimens 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 Experiments

HyFRC compared with conventional concrete

Strain

Control (conventional) concrete

HyFRC

0

0.002

0.004

0.008

0.01

0.012

0.006

0

2

5

7

Stress (ksi)

4

6

1

3

HyFRC has stable,
extended softening
behavior on its own

Compression Experiments

High confinement ratio not needed with SC
-
HyFRC


SCC (1.91%)

SC
-
HyFRC

SCC

SC
-
HyFRC

SCC

r
v

= 0.95%

r
v

= 0.32%

r
v

= 0.49%

1”

2”

3”

Compression Experiments

Confined HyFRC Results (2” spacing)

Plain

HyFRC

SC
-
HyFRC

Delay in
damage
initiation and
damage
progression

Extensive
spalling

Compression Experiments

No damage localization in SC
-
HyFRC

r
v

=0.95%

SC
-
HyFRC

Plain SCC

r
v

=1.91%

r
v

=0.95%

r
v

=0.95%

Experimental Program

Tension 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 experiments

Questions

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 Experiments

Two specimen designs evaluated

Tension Stiffening Experiments

Specimen 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 Experiments

Specimen design and set
-
up validation

Dogbones
-

Typical Failures

ECC3
-
4
-
1

ECC3
-
4
-
2

SC
-
HyFRC
-
4
-
2

HyFRC
-
4
-
2

SC
-
HyFRC
-
4
-
1

HyFRC
-
4
-
1

Rebar f
y
A
s

+ ECC stress block

Tension Stiffening Experiments

ECC Dogbones
–

Preliminary Data

Average strength of plain
HyFRC

dogbones

~3
-
4 kips

Tension Stiffening Experiments

HyFRC 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 Work

Experiments and Model Development

Plate

Beam

ECC

ECC

Material Characterization for Modeling

Can simple material testing be used to predict performance
in reinforced components?

12”

Plate

Plate

Inverse analysis of flexural response
to estimate uniaxial tensile data

ECC

ECC

Material Characterization for Modeling

Can 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