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
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