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Steel Structures 7 (2007) 69-75 www.ijoss.org
Seismic Behavior of Composite Shear Wall Systems
and Application of Smart Structures Technology
Qiuhong Zhao1 and Abolhassan Astaneh-Asl2,*
1Assistant Professor, University of Tennessee, Knoxville, Civil and Environmental Engineering Department,
109A Perkins Hall, Knoxville, TN 37996-2010, USA2Professor, University of California, Berkeley, Civil and Environmental Engineering Department,
781 Davis Hall, Berkeley, CA 94720, USA
Abstract
Shear wall systems are one of the most commonly used lateral load resisting systems in high-rise buildings. This paperconcentrates on the experimental and analytical studies of two composite shear wall systems and presents a summary anddiscussion of research results. In addition, the paper discusses application of smart structures technology into the design of thesesystems. The composite shear wall system studied herein consists of a steel boundary frame and a steel plate shear wall witha reinforced concrete wall attached to one side. The steel plate shear wall is welded to the boundary frame and connected tothe reinforced concrete wall by bolts. In the system called “traditional” the reinforced concrete wall is in direct contact withthe boundary steel frame, while in the system called “innovative” there is a gap in between.
Keywords: Smart Structures Technology, Composite Shear Wall, Seismic Engineering, Cyclic Test
1. Introduction
Reinforced concrete shear walls have been widely used
as lateral load resisting system in the past in high-rise
buildings, but there were always concerns on the local
strength, ductility and construction efficiency of these
systems in steel high-rise buildings, especially in high
seismic zones. In recent years, more and more steel plate
shear walls have been used with satisfactory results on
construction efficiency and economy. Yet there were still
concerns on overall buckling of the steel plates that will
result in reduction of the overall shear strength, stiffness
and energy dissipation capacity (Zhao, 2004), as well as
large inelastic deformation of the steel plates that will
result in large cyclic rotations of the moment connections
and large inter-story drifts (Allen, 1980). On the other
hand, composite shear walls might compensate for the
disadvantages of reinforced concrete shear walls and steel
shear walls and combine the advantages together. The
composite shear walls have been used recently in a few
modern buildings including a major hospital in San
Francisco (Dean, 1977), but not as common as the other
lateral load resisting systems. Therefore, seismic behavior
of these systems and corresponding design guidelines are
of high interest to design engineers. As a result, a project
was conducted at the University of California, Berkeley
to investigate the seismic behavior of two composite
shear wall systems through large scale cyclic tests and
advanced finite element analyses.
2. Project Background
The composite shear wall project described in this paper
concentrated on the seismic behavior of two composite shear
wall systems denoted as “traditional” and “innovative”
(designed by the second author), as shown in Fig. 1. Both
systems are “dual” lateral load resisting system as defined in
current codes (ICBO, 1997), and consist of a composite
shear wall (primary system) welded inside a moment frame
(secondary system) in a single-bay. The composite shear
wall is made of a steel wall and a reinforced concrete (RC)
wall connected together by bolts. In the traditional system,
the four edge surfaces of the RC wall are in direct contact
with the steel boundary frame, while in the innovative
system there is a gap in-between. It is anticipated that by
introducing the gap, the performance of the RC wall under
severer seismic events could be improved, and the RC wall
could be pre-cast and bolted to the steel wall on site to
further increase construction efficiency.
3. Experimental Studies
3.1. Cyclic test on composite shear wall system
Two half-scale specimens were constructed representing
sub-assemblies of a generic building over three floors
with the innovative composite shear wall system (Specimen
*Corresponding authorTel: 510-642-4528E-mail: [email protected]
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70 Qiuhong Zhao and Abolhassan Astaneh-Asl
One) and the traditional composite shear wall system
(Specimen Two) as the lateral load resisting system. Each
specimen included two full stories in the middle and two
half-stories at the top and bottom.
Structural components of the specimens are shown in
Table 1. As illustrated before, both specimens had exactly
the same components, except that in Specimen One there
was a gap of 32 mm between the RC wall edges and the
steel boundary frame in the middle two stories. The wide
flange (WF) columns and beams were made of A572
Grade 50 steel with yield stress of 345 MPa, and the steel
wall plate was made of A36 steel with yield stress of 248
Table 1. Components of composite shear wall test specimens
Steel wall plate thickness
Pre-cast RC wallWall bolts dia.
Beamsection*
Columnsection*Thickness Rebar dia. Rebar spacing Reinf. ratio
4.8 mm 76 mm 10 mm 102 mm 0.92% 13 mm W12 × 26 W12 × 120
*Cross section properties refer to the AISC Manual (AISC, 1994).
Figure 1. Main components of composite shear wall system.
Figure 2. A composite shear wall Specimen with details of RC wall.
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Seismic Behavior of Composite Shear Wall Systems and Application of Smart Structures Technology 71
MPa. The concrete had a minimum f’c of 28 MPa. The
test specimen and details of the reinforced concrete walls
are shown in Fig. 1 and 2.
Test set-up for the composite shear wall tests is shown
in Fig. 3. During the test, cyclic shear displacements were
applied by the actuator to the top of the specimen through
the top loading beam, and the shear force was transferred
to the lab floor by the bottom reaction beam and reaction
blocks. As shown in Fig. 4, the same cyclic displacements
were applied to both specimens, which were established
according to the specifications for Qualifying Cyclic Tests
of Beam-to-Column and Link-to-Column Connections in
Seismic Provisions for Structural Steel Buildings (AISC
1997). A set of linear variable displacement transducers
(LVDT) and strain gauges were installed on the test
specimens and test set-up in order to measure the
displacement and strain at critical locations of the
specimen and monitor slippage of the test set-up.
3.2. Cyclic behavior of composite shear wall system
Specimen One, with a 32 mm gap around the RC wall,
behaved in a very ductile and desirable manner. Up to
overall drifts of about 0.006, the specimen was almost
elastic. At this drift level some yield lines appeared on the
beams as well as column base. At overall drifts of about
0.012, the compression diagonal in the steel wall panels
was buckling and diagonal tension field was forming. The
specimen could tolerate 33 cycles, out of which 27 cycles
were inelastic, before reaching an overall drift of 0.044
and maximum shear strength of about 2790 kN. At this
level of drift, fractures were widespread in the walls and
frame members due to low-cycle fatigue, and the bolts
connecting the steel wall and RC wall were almost gone.
Shear strength of the specimen dropped to about 80% of
the maximum capacity, and the specimen was considered
failed.
Specimen Two also behaved in a ductile manner. Up to
overall drifts of about 0.006, the specimen was almost
elastic. At this drift level some yield lines appeared on the
bottom and middle beam webs as well as column base
plate. The specimen was able to reach cyclic overall drift
of 0.042 after undergoing 23 cycles, 17 of the cycles
being inelastic. The maximum shear force reached was
about 3020 kN during the 19th cycle. Throughout the test,
the gravity load carrying column remained essentially
stable while non-gravity carrying lateral load resisting
elements underwent well-distributed and desirable yielding.
During the 23rd cycle, the upper steel shear wall plate
fractured totally along the north and bottom edges due to
low-cycle fatigue, and the bolts connecting the steel wall
and concrete wall were almost gone. Shear strength of the
specimen dropped to about 80% of the maximum
capacity, and the specimen was considered failed. Figure
5 shows both specimens after the test, as well as the
hysteresis curve for the third story of both specimens.
Based on the test observations and post processing of
Figure 3. Composite shear wall specimen and test set-up.
Figure 4. Loading history of composite shear wall tests.
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72 Qiuhong Zhao and Abolhassan Astaneh-Asl
test data, it is clear that in the innovative composite shear
wall system, damage to the concrete wall was much less
than in the traditional composite shear wall system. The
steel wall didn’t have excessive global buckling compared
to some other steel shear wall tests conducted at Berkeley
(Zhao 2004); instead the buckling happened locally between
the bolts. The sequence of yielding of components was
very desirable with yielding showing in WF beams and
steel walls first. At the end of the test, the WF columns
showed yielding at the base but didn’t buckle. The
composite shear walls and WF beams did yield extensively
and dissipated energy, which made the composite shear
wall system very ductile with inter-story drift over 4.4%.
Therefore an R-factor of 8.0, in the codes today, was
confirmed. An R of 9-10 is more appropriate.
4. Analytical Studies
Finite element analyses were conducted on the composite
shear wall specimens, along with parametric studies. Two
models were constructed with model one representing
Specimen One (innovative system) and model two
representing Specimen Two (traditional system), as
shown in Fig. 6. Accordingly, there was a 32 mm gap
between the four edge surfaces of the RC wall and the
boundary frame in model one, while there was no gap in
Figure 5. Composite shear wall specimens after the test and hysteresis curve for the third story.
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Seismic Behavior of Composite Shear Wall Systems and Application of Smart Structures Technology 73
model two. All the other geometric, material and element
properties as well as boundary conditions of these two
models were the same. In order to facilitate the
calculation process, a negligible gap was introduced
between the RC wall edge surfaces and the boundary
frame in model two, as well as between the steel wall and
RC wall in both models.
Most of the structural components were modeled as
nonlinear shell elements, except for the bolts which were
modeled as 1-D beam elements. The steel material
properties were simplified to a bilinear model considering
strain-hardening, and the reinforced concrete material
property was simplified to an elasto-plastic model
considering the contribution from rebars. In addition, the
elastic modulus E of the steel material for plates was
reduced by 30% to take into account for initial warping,
geometric imperfections, residual stresses, etc.
MSC Nastran was used to conduct the nonlinear push-
over analysis on the structural system. An implicit nonlinear
solver was used to consider geometric and material
nonlinearities during the push-over analyses, as well as
contact phenomena (MSC Corp., 2005). In order to simulate
the contact between the RC wall and the surrounding
steel surfaces, the RC wall and the surrounding steel parts
were defined as separate contact bodies. By applying
contact methodology, motion of the RC wall and the
surrounding steel parts on the boundary gap would be
monitored, so that transferring of forces and stresses on
the boundary would be conducted once the steel and
concrete surfaces get into contact.
The lateral force vs. overall displacement curve from
the push-over analysis matched with the test results to a
reasonable extent, for both specimens as shown in Fig. 7.
Parametric studies were developed on this basis. Three
cases were run for the composite shear wall systems to
identify the key design parameters. In each case, only one
parameter in the structural model was modified.
Parametric studies showed that for the composite shear
wall system studied in this paper, the steel wall is the
major component and its stiffness and strength contribute
the most to the overall system stiffness and strength.
Increasing the steel wall thickness would be a very
effective way to strengthen the whole system; however,
premature failure of the system might occur if the WF
columns were not strong enough. In the mean time, using
higher strength steel for the steel wall would also be an
effective way to strengthen the composite shear wall
system, while using high strength concrete for the RC
wall wouldn’t affect the system behavior as much.
5. Application of Smart Structures Technology
Smart structures technology involves development of
intelligent material or structures that can monitor their
own condition, detect impending failure, control damage,
and adapt to changing environments (Chong, 2003). The
idea of smart structures technology was shown in the
design of the innovative composite shear wall system
Figure 6. Finite element models of composite shear wallspecimens.
Figure 7. Comparison of experimental and analyticalpush-over curves for composite shear wall specimens.
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74 Qiuhong Zhao and Abolhassan Astaneh-Asl
which helps control structural damage and adapt
structural behavior to external seismic events.
By introducing the gap in the innovative composite
shear wall system, it is anticipated that the system lateral
stiffness would be reduced and the RC wall behavior
would be improved under severer seismic events. In the
traditional composite shear wall system, both the steel
and RC walls will be active in resisting lateral loads as
soon as a lateral displacement is applied. As a result,
larger base shear will be present in the structure due to
relatively larger stiffness of the combined system, and the
RC wall could be damaged under relatively small lateral
displacement. In the innovative composite shear wall
system, however, due to the existence of the gap, the RC
wall will not get involved in resisting lateral loads until the
inter-story drift has reached a certain value, as shown in
Fig. 8.
When the drift is under the specified value, only steel
shear wall and the boundary moment frame provide
strength, stiffness and ductility, and the role of RC wall is
to provide out-of-plane bracing for the steel plate. When
the drift is over the specified value, the gap is closed at
corners and both steel and RC walls become active and
provide strength, stiffness and ductility. Then the
participation of RC wall brings in the much needed extra
stiffness to help reduce the drift and P-∆ effects,
compensates for loss of stiffness of steel shear wall due to
yielding, and helps in preventing lateral creep and
collapse failure of the structure due to P-∆ effects.
An additional possible application of the smart structures
technology to the composite shear wall systems would be
the use of visco-elastic material as a filler in the gap
around the RC walls in the innovative system, such that
more damping could be introduced to the system and the
energy dissipation capacity of the whole system would be
increased under seismic effects. The introduction of smart
materials such as replacing the concrete with a lighter
material that could provide enough bracing to the steel
wall would also be a potential application.
6. Conclusions
The projects described in this paper addressed the
issues of cyclic behavior of two composite shear wall
systems, and proposed seismic design recommendations.
Through the experimental studies, it is clear that both
systems were very ductile under large cyclic displacements
with maximum inter-story drifts over 4.2%. Therefore an
R factor of 8.0 or even 9.0 could be used in the seismic
design of these systems. The experimental studies also
showed the importance of keeping the gravity load
carrying members in these systems intact under seismic
effects, while the non-gravity carrying members could
yield extensively and dissipate energy.
The project also verified the idea of “innovative composite
shear wall system” and compared its performance with
the traditional composite shear wall system. Experimental
results showed that by bolting a RC wall to a steel shear
wall on one side, the excessive global buckling of the
steel wall was prevented. In the mean time, the gap in the
innovative composite shear wall system introduced more
stable behavior and reduced the damage to the concrete
wall.
The analytical studies on the composite shear wall
system showed some of the major factors that control the
overall shear strength of the system. Further refined
analytical studies on more parameters would help in
identifying the key parameters for seismic design.
Smart structures technology could be applied to the
design and construction of the composite shear wall
systems, and further improvement of system behavior
could be achieved by introducing new materials.
Acknowledgments
This project was funded by the National Science
Foundation, Directorate of Engineering, Civil and
Mechanical Systems. The technical assistance and input
from Program Directors Dr. S. C. Liu and Dr. P. Chang at
NSF were much valuable and sincerely appreciated. The
research was part of the U.S. Japan Cooperative Research
on Composite and Hybrid Structures of the National
Science Foundation. The guidance and technical input of
all involved in the program, in particular Professors
Stephen Mahin and Subhash Goel, directors and organizers
of the program are sincerely appreciated. The Structural
Steel Educational Council, American Institute of Steel
Construction (AISC) and the Herrick Corporation also
provided valuable input and support. Judy Liu, formerly
graduate student at the University of California, Berkeley
provided valuable help in developing, analyzing and
designing the test set-up. Her work is very much
appreciated. Ricky Hwa, undergraduate research assistant
participated in preparing specimens, instrumentation, and
Figure 8. Function of gap in the innovative compositeshear wall system.
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Seismic Behavior of Composite Shear Wall Systems and Application of Smart Structures Technology 75
conducting tests. His dedicated and valuable work was
very helpful to the success of the project. Finally, this
experimental program could not have been completed
without the resources of the laboratory and staff of the
Department of Civil and Environmental Engineering at
the University of California at Berkeley.
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