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: astaneh@ce.berkeley.edu

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.

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.

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.

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.

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.

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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