FIBER REINFORCED CONCRETE IN SHEAR
WALL COUPLING BEAMS
Gustavo J. Parra

Montesinos
C.K. Wang Professor of Structural Engineering
University of Wisconsin

Madison
James K. Wight
Frank E. Richart Jr. Collegiate Professor
University of Michigan
Cary Kopczynski
Principal, Cary Kopcyznski & Co.
OUTLINE
•
Current design practice for coupling beams
•
Research motivation
•
Classification of Fiber Reinforced Concretes (FRCs)
•
Experimental program
•
Coupling beams
•
Coupled walls
•
Implementation of fiber reinforced concrete coupling beams
into practice
•
Two or more walls connected
by short beams referred to as
coupling beams
•
Commonly used in medium

and high

rise structures in
combination with RC or steel
moment frames
COUPLED WALLS
•
Typical span

to

depth ratios between 1.5 and 3.5
•
Diagonal reinforcement, designed to carry the entire shear
demand, is required in most cases
•
Column

type transverse reinforcement must be provided to
confine either diagonal reinforcement or entire member
•
Maximum shear stress of 10√
f
c
’
(psi)
•
Little longitudinal reinforcement, terminated at the wall near
the coupling beam end
CURRENT COUPLING BEAM DESIGN
PRACTICE IN USA
(Lequesne, Parra and Wight)
TYPICAL COUPLING BEAM DESIGN
•
Reinforced concrete coupling beams require intricate
reinforcement detailing to ensure stable seismic behavior,
leading to severe congestion and increased construction
cost
•
Use of a material with tension ductility and confined
concrete

like behavior should allow for substantial
simplification in confinement and shear reinforcement
without compromising seismic behavior
MOTIVATION
FIBER REINFORCED CONCRETE
•
Concrete reinforced with discontinuous fibers
•
Commonly used steel fibers have deformations to improve
bond with surrounding concrete. However, fibers are
ultimately expected to pullout
Constituents
Concrete matrix in fiber reinforced concrete is made of same
constituents used in plain concrete
•
Aggregates (fine and course)
•
Cement
•
Water
•
Mineral admixtures
•
Water reducing agents (high

range water

reducing agents)
MATERIAL

RELATED ASPECTS
Aggregates
•
Sufficient fine aggregates to ensure adequate volume of
paste
•
Control volume and size of course aggregate
–
Increase in course aggregate size has been associated with
poor fiber distribution and a reduction in tensile performance
–
Maximum aggregate size in fiber reinforced concrete used in
coupling beams has been limited to ½ in.
Workability
•
For large fiber dosages as used in coupling beams, use self

consolidating mixture or a mixture with high slump (at least 8
in.) prior to addition of fibers
MATERIAL

RELATED ASPECTS
•
Regular concrete matrix (1/2 in. max. aggregate size)
•
1.5% volume fraction of high

strength hooked steel fibers (
l
f
=1.2
in.;
d
f
= 0.015 in.)
(Naaman et al.)
USE OF SELF

CONSOLIDATING HPFRC
(Naaman et al.)
Deflection hardening vs. softening
Strain hardening vs. softening
(Naaman and Reinhardt 2003)
•
Based on bending and tension behavior
cc
pc
cc
pc
FRC typical;
strainsoftening
Matrix
HPFRCC typical
(Strainhardening and
multiple cracking)
STRESS
STRAIN
(or elongation)
cc
f
r
f
c
u
Deflectionsoftening
Matrix
(Deflectionhardening
and multiple cracking)
LOAD
DEFLECTION
MOR
cc
pc
cc
pc
FRC typical;
strainsoftening
Matrix
HPFRCC typical
(Strainhardening and
multiple cracking)
STRESS
STRAIN
(or elongation)
cc
f
r
f
c
u
Deflectionsoftening
Matrix
(Deflectionhardening
and multiple cracking)
LOAD
DEFLECTION
MOR
CLASSIFICATION OF FRCs
FIBER REINFORCED CONCRETE IN
EARTHQUAKE

RESISTANT COUPLING BEAMS
Fiber reinforced concrete with
tensile strain

hardening behavior
(HPFRC) and compression behavior
similar to well

confined concrete
RC
HPFRC
13
0
0.5
1
1.5
2
2.5
3
0
0.005
0.01
0.015
0.02
0.025
0.03
Tensile Stress (MPa)
Tensile Strain
Damage Localization
0
10
20
30
40
50
0
0.005
0.01
0.015
0.02
Compressive Stress (MPa)
Compressive Strain
•
High

strength hooked steel fibers have been the most
investigated fiber type for use in coupling beams
•
Volume fraction = 1.5% (200 lbs/cubic yard)
FIBER REINFORCED CONCRETE IN
EARTHQUAKE

RESISTANT COUPLING BEAMS
SLENDER COUPLING BEAMS (
l
n
/
h
≥ 2.2)
#3
#3
#4
6 in.
24 in.
6.5 in.
3.25 in.
#4
66 in.
#6
#5
7 in.
•
Target shear stress 8

10√f’
c
, psi
•
Approximately 25% of shear resisted by diagonal bars
,
45% of shear carried by stirrups, and 30% of shear resisted by
HPFRC
•
Transverse reinforcement ratio = 0.56%
SLENDER COUPLING BEAM (
l
n
/
h
= 2.75)
8
6
4
2
0
2
4
6
8
0
2
4
6
8
10
12
Drift (%)
Shear Contribution, (psi)
CB1
Diagonal bars
Stirrups
HPFRC
'
c
f
8
6
4
2
0
2
4
6
8
0
2
4
6
8
10
12
Drift (%)
Shear Contribution, (psi)
CB2
Stirrups
Diagonal bars
HPFRC
'
c
f
8
6
4
2
0
2
4
6
8
0
2
4
6
8
10
12
Drift (%)
Shear Contribution, (psi)
CB3
Diagonal bars
Stirrups
HPFRC
'
c
f
CB

1
CB

2
CB

3
SHEAR CONTRIBUTION FROM DIAGONAL BARS
(Sektik, Parra and Wight)
•
Complete elimination of diagonal reinforcement in coupling
beams with length

to

depth ratios ≥ 2.2
•
No special confinement, except for beam ends
•
Shear strength up to 10
√
f’
c
(psi)
COUPLING BEAM BEHAVIOR
ELIMINATION OF DIAGONAL BARS (
l
n
/
h
≥ 2.2)
(Sektik, Parra and Wight)
COUPLING BEAM BEHAVIOR
SLENDER COUPLING BEAM DESIGN (
l
n
/
h
≥ 2.2)
BEHAVIOR of COUPLING BEAM with NO
DIAGONAL BARS (
l
n
/
h
= 3.3)
(Sektik, Parra and Wight)
10
5
0
5
10
10
8
6
4
2
0
2
4
6
8
10
0.8
0.4
0
0.4
0.8
Average shear stress [(
f
c
'
)
1/2
, psi]
Drift (%)
Average shear stress [(
f
c
'
)
1/2
, MPa]
SLENDER COUPLING BEAM with NO
DIAGONAL BARS AT 6% DRIFT
(Sektik, Parra and Wight)
BEHAVIOR of COUPLING BEAM with NO
DIAGONAL BARS (
l
n
/
h
= 2.2)
(Comforti, Parra and Wight)
10
8
6
4
2
0
2
4
6
8
10
1500
1000
500
0
500
1000
1500
Drift (%)
Shear Stress (psi)
•
Diagonal bars can be eliminated in HPFRC coupling
beams with
l
n
/
h
≥ 2.2 when reinforced with a 1.5% volume
fraction of high

strength hooked steel fibers and subjected
to shear stress demands up to the upper limit in ACI
Building Code
•
When diagonal reinforcement was used in slender
HPFRC coupling beams, shear resistance provided by
that reinforcement was estimated at or below 15% of the
total shear, which suggested elimination of diagonal bars
in such beams
CONCLUSIONS
–
SLENDER COUPLING BEAMS
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