00178 Minjuan He - Timber Design Society

EVALUATION OF LATERAL PERFORMANCE OF TIMBER-
STEEL HYBRID LATERAL RESISTANT SYSTEM THROUGH
EXPERIMENTAL APPROACH
Minjuan He 1 , Zheng Li 2
ABSTRACT: A multi-storey timber-steel hybrid structure, which is composed of a steel frame and a light wood-frame
shear wall, is introduced. Light wood-frame shear walls are used as infill between steel columns to form a timber-steel
hybrid system to resist the lateral loads of the structure. In this paper, the lateral performance of a timber-steel hybrid
structure is studied through pseudo static experiments. The dual characteristics of the steel frame and wood shear wall
interactions are discussed. The effectiveness of infill light wood-frame shear walls in resisting lateral loads and their
influence on the steel frame's behaviour are obtained from experiments of a single-storey specimen. At the same time,
the strength, rigidity, hysteretic behaviour and failure modes of a timber-steel hybrid lateral resistant system are
investigated. Experimental results show infill wood shear walls can work together with the steel frame, improving
structural behaviour. The steel frame and wood shear wall roughly maintain their own lateral load bearing
characteristics and show complementary behaviour in the hybrid system. This research aims to develop an
environmental friendly prefabricated structural system and explores the application of timber in multi-storey buildings.
KEYWORDS: Timber-steel hybrid structure, Lateral performance, Quasi-static experiment, Dual characteristics
1 INTRODUCTION 12
Wood is a renewable and environmental friendly
material. The production process of wood products
consumes less energy than those of concrete and
masonry, which makes it a desirable building material
for a low carbon economy. However, the limitations of
wood-frame construction, where wood is usually used in
low-density form, have been exposed in recent years;
and, researchers have begun to seek the application of
wood in multi-storey buildings.
In order to explore multi-storey timber buildings, there
are mainly two ways to improve the strength and rigidity
of wood. One is the development of stronger wood
building materials by means of gluing, etc. This method
continues the advantages of timber buildings, such as
easy to manufacture, light weight and fast erection, but it
uses a lot of wood, and its fire-resistant property is still
under discuss. The other solution is hybridization.
With the help of hybridization of wood and other
materials, the shortcomings of wood can be decreased, or
even eliminated. There are also two levels of
hybridization: the composite level and the structural
1 Minjuan He, Department of Building Engineering, Tongji
University, Siping Road 1239, Shanghai, China. Email:
hemj@tongji.edu.cn
2 Zheng Li, Department of Building Engineering, Tongji
University, Siping Road 1239, Shanghai, China. Email:
09lizheng@ tongji.edu.cn
level. For example, timber-concrete composite floors,
post-tensioning laminated veneer lumber (LVL) in [1]
and timber-steel composite columns and beams in [2]
can all be considered in the composite level of
hybridization, which means different materials resisting
loads together in one structural member. The structural
level of hybridization indicates a structure that includes
different load bearing members, such as a masonry
structure with a timber roof. These can be regarded as
timber-based hybrid structures, which can be an effective
approach for the development of multi-storey timber
buildings. Research related to hybridization is currently
flourishing.
This paper introduces a multi-storey timber-steel hybrid
structure that is composed of a steel frame and light
wood-frame diaphragms and shear walls. Due to the
light weight of wood-frame diaphragms and shear walls,
the vertical loads, horizontal seismic action and
foundation cost of a timber-steel hybrid structure are
maximally reduced. There will also be a higher level of
prefabrication and thus a reduced workload on site. Due
to the desirable heat insulating property of wood, a
healthy and comfortable living environment will be
created.
As to the structural details of timber-steel hybrid
structure, light wood-frame diaphragms combined with
steel beams serve as a floor system to resist vertical
loads and transfer lateral loads, while light wood-frame
shear walls are used as infill in steel frames, as a hybrid

system to resist lateral loads. The two systems act
together to achieve good structural behaviours, and the
interactions of the two will be a key issue of timber-steel
hybrid structure or similar structural systems as in [3,4].
2 EXPERIMENT
2.1 DESIGN OF THE EXPERIMENT
A single-storey specimen was designed to study the
lateral performance of a timber-steel hybrid structure.
The layout of the specimen is shown in Figure 1, and the
corresponding cross sections of the steel frame are listed
in Table 1. The height of the specimen was 2.8 m, and
the width and length of the specimen were 3.0 m and 6.0
m, respectively. There were three timber-steel hybrid
lateral resistant systems in the specimen located at axes 1,
2 and 3. In this paper, the three hybrid systems are
referred as TS-1, TS-2 and TS-3.
introduced as two subsystems, as shown in Figure 3. The
light wood-frame shear wall filled in the area between
steel columns; and, in order to reduce the relative
displacement between the two subsystems, the top plate
and side studs of the wood shear wall were connected to
steel frame by bolts, as shown in Figure 4. Anchor bolts
had a spacing of 1 m, and hold-downs were also installed.
Table 2: Construction details of wood shear walls and
diaphragms
Panel
Type
OSB
Thick(mm) 15
Diameter×length
Sheathing
3.8×82
(mm×mm)
Nail
Spacing Perimeter 150 (75)
(mm) Space 300 (150)
type SPF (II c )
Joist
Cross section
(mm×mm)
38×140
Spacing(mm) 406 (300)
Remarks: Numbers in the brackets are for diaphragms
Figure 1: Layout of the specimen
Table 1: Cross sections of steel frame
Items Cross section
Yield point
(kN/mm 2 )
Steel column H150X150X7X10 235
Steel beam H150X100X6X9 235
A light wood-frame diaphragm served as the floor
system and a steel frame combined with light woodframe
shear wall served as the lateral resistant system of
the specimen. The construction details of the wood
diaphragms and shear walls are listed in Table 2, and the
setup of the specimen is shown in Figure 2.
2.2 FORMATION OF TIMBER-STEEL HYBRID
LATERAL RESISTANT SYSTEM
Steel and wood are different materials; the yield strength
of steel is about twenty times larger than the
compression strength of wood, while the Young's
modulus of dimension lumber SPF (spruce-pine-fir) is
only one twentieth of that of steel. Therefore, the
structural formation of a timber-steel hybrid lateral
resistant system becomes a key issue in ensuring the
collaborative work of steel and wood.
In the timber-steel hybrid lateral resistant system, the
steel frame and the light wood-frame shear wall were
Figure 2: Setup of the specimen
The top and bottom flanges of the steel beams were
welded to the steel column, and the web of the steel
beam was connected to the steel column with bolts. In
this way, the beam-column joint of the steel frame could
be regarded as fully rigid.
2.3 LOADING METHOD
Load was applied to the top left corner of the specimen
by two hydraulic actuators and distribution beams, which
could apply the middle loading point with twice as much
force as the force applied sideways, as shown in Figure 5.
2.3.1 Loading cases
Three loading cases were carried out to study the
performance of the timber-steel hybrid lateral resistant
system and the whole structure. The loading cases are
listed in Table 3.

2.3.2 Monotonic loading protocol
The monotonic loading process was aimed at studying
the initial lateral resistant stiffness of the steel frame
before and after the installation of the wood diaphragm
and shear walls. Before the formal loading process, a 5
kN force was applied to eliminate the gaps in the
connections between the loading equipment and the
specimen. The maximum monotonic load was 50 kN and
was divided into 5 steps with 10kN/step.
Figure 3: Construction details of timber-steel hybrid
lateral resistant system
2.3.3 Cyclic loading protocol
The cyclic loading process was aimed at examining the
hysteretic performance of the timber-steel hybrid lateral
resistant system. The loading protocol was determined
according to Chinese code “Specification of test methods
for earthquake resistant building” in [5,6] and ISO 16670
in [7]. The elastic lateral resistance capacity and ultimate
displacement of the specimen were about 150 kN and
100 mm, respectively, according to theoretical analysis.
In the cyclic loading process, the load was first
controlled by force; and, when the specimen went into its
plastic stage, the load was then controlled by
displacement. The cyclic loading protocol is shown in
Figure 6. It should be noted that the force was the total
force applied on the specimen (P+2P+P), and the
displacement load was controlled by the midpoint of the
specimen (where the load was 2P).
Figure 4: Connection of side studs of wood shear wall
and steel frame
Figure 6: Cyclic loading protocol
Figure 5: Loading method
Table 3: Loading cases
Case Specimen description Loading method
1 Open steel frame Monotonic
2
Steel frame with wood
diaphragm and shear walls
Monotonic
3
Steel frame with wood
diaphragm and shear walls
Cyclic
2.4 DATA MEASUREMENT METHOD
Six displacement gauges, as shown in Figure 1, were
installed on the top corners of the specimen to monitor
its lateral displacement. Strain gauges were pasted on the
steel frame to detect the strain of the steel columns and
beams. Each timber-steel hybrid lateral resistant system
had 18 strain gauges on the steel frame. Their
distribution is shown in Figure 7.
Strain gauges S3-S6 and S13-S16, located at the 1 m
length of the steel columns, were used to obtain the exact
shear force in the steel frame. This section of steel
column was always in the elastic stage during the test,
according to a numerical analysis. Figure 8 and
Equations (1) and (2) show the method of calculating the
shear force in each steel column.

⎧ N M
+ = ε
⎪ EA EW
⎨
⎪ N M
− = ε
⎪⎩ EA EW
Q
M
− M
L
max
min
(1)
u d
= (2)
where N = axial force, M = bending moment, ε = strain,
E = Young’s modulus, A is the section area, W is the
bending modulus and Q is the shear force in steel
columns or wood shear walls.
the loading of the specimen without the diaphragm, the
displacement of the mid-column was obviously larger
than the side columns.
3.2 CYCLIC LOADIND PERIOD
Table 4 and Figure 9 give descriptions of the
experimental phenomenon and failure modes in cyclic
loading period.
In addition, no failure was found in the wood frame
during the whole period of the cyclic test. This is quite
different from the failure modes of the lateral test of
single wood shear walls, which always contained the uplift
failure of studs.
Table 4: Experimental phenomenon in cyclic loading
Figure 7: Location of strain gauges on the steel frame
Figure 8: Method to calculate the shear force in each
steel column
3 EXPERIMENTAL PHENOMENON
3.1 MONOTONIC LOADIND PERIOD
In the monotonic loading cases, no failures were found
in the steel frame and wood shear walls. There was also
no obvious deformation of the wood diaphragm. During
Loading Step Experimental phenomenon Figure
±50kN - -
±75kN
±100kN
±125kN
±150kN
±20mm(1/140)
Slight slope of edge nails of
wood shear walls; noise of
collision of wood and steel.
Slope of the whole sheathing
±25mm(1/112) panels could be observed.
-
±35mm(1/80) Failure of nail connections
±45mm(1/60)
(Nail pulling through -
sheathing panels).
±55mm(1/50) Noise of cracking and corner
±65mm(1/43)
shear failure of sheathing 8-(a)
panels.
±75mm(1/37)
Most of the edge nail
connections were broken,
specimen went into its
8-(b)
ultimate state.
±95mm(1/30)
Failure of weld in columnbeam
connections of steel 8-(c)
frame
±115mm(1/24)
Failures were found in 70%
8-(d),
of the edge nail connections,
(e)
specimen was damaged.
Remarks: Number in the bracket is inter-story drift ratio.
4 EVALUATION OF LATERAL
PERFORMANCE OF TIMBER-STEEL
HYBRID LATERAL RESISTANT
SYSTEM
4.1 INITIAL STIFFNESS
The effectiveness of infill wood shear walls in improving
the initial lateral stiffness of steel frame was investigated
through loading cases 1 and 2. Using TS-2 for
explanation in this part, the shear force could be
calculated using Equations (1) and (2). Although the
total force applied on the specimen in cases 1 and 2 were
both 50 kN, the exact shear force in the open frame's
mid-columns and TS-2 were different. This was caused
by the diaphragm effect, but had little influence on the
issue discussed in this section.
-

It was found that the infill wood shear wall improved the
initial stiffness of the open steel frame from 2.18 kN/m
to 5.96 kN/m, more than 2.5 times, as shown in Figure
10.
using Equation (1), where P peak is the maximum load on
the load-displacement curve, and Δ 0.4Ppeak is the
displacement when the load reached 40% of maximum
load. The yield load can be determined using Equation
(1), an ideal elastic-plastic curve circumscribing an area
equal to the area enclosed by the envelope curve
between the origin, the ultimate displacement, and the
displacement axis, as shown in Figure 11. The ductility
is calculated using Equation (1).
K
= 0.4 P / Δ (3)
e peak 0.4P peak
(a) Corner shear failure
of sheathing panels
(b) Failure of edge nail
connections
⎧
P
⎪
⎨
⎪
⎪
P
⎩
⎛ 2A
⎞
2A
= Δ − Δ − K Δ ≥
⎝
⎠
Ke
2A
= 0.85 P Δ <
K
2 2
yield ⎜
u u e u
K ⎟
e
2
yield peak u
e
(4)
(c) Failure of weld in
steel frame
(d) Serious slope of
sheathing panels
μ = Δ / Δ (5)
u
Since the hysteresis curves were quite symmetrical, only
the positive backbone circles were used in this analysis.
The backbone curves of TS-1, TS-2 and TS-3 in loading
case 3 are shown in Figure 12, and the calculation results
of the EEEP parameters are listed in Table 5.
yield
(e) Shear failure of nails
Figure 9: Failure modes in cyclic loading stage
Figure 11: EEEP curve
Since the hysteresis curves were quite symmetrical, only
the positive backbone circles were used in this analysis.
The backbone curves of TS-1, TS-2 and TS-3 in loading
case 3 are shown in Figure 12, and the calculation results
of the EEEP parameters are listed in Table 5.
Figure 10: Comparison of initial stiffness
4.2 ANALYSIS OF BACKBONE CURVES
The elastic stiffness and yield load of the timber-steel
hybrid lateral resistant system can be defined from the
EEEP (equivalent energy elastic plastic) curve,
according to ASTM E2126-09 in [8]. The elastic
stiffness K e of a lateral resistant system can be calculated
Figure 12: Positive backbone curves of timber-steel
hybrid lateral resistant system

Table 5: Calculation results of EEEP parameters
Ultimate
bearing
capacity
P peak (kN)
Elastic
stiffness
K e
(kN/mm)
Yield
load
P yield (kN)
Ductility
μ
TS-1 119.52 3.58 118.29 2.62
TS-2 133.32 4.07 120.93 3.87
TS-3 126.84 3.31 118.54 3.49
the wood shear wall went into the plastic stage. The steel
frame carried most of the lateral loads after the wood
shear wall was damaged at about 95 mm.
4.3 HYSTERETIC CHARACTERISTICS
4.3.1 Hysteresis curve
TS-2 was chosen for the analysis of the hysteretic
characteristics of the timber-steel hybrid lateral resistant
system. The hysteresis curve of TS-2 is shown in Figure
13.
Figure 14: Shear force in timber-steel hybrid lateral
resistant system
Q3= P−Q1− Q2
(6)
Figure 13: Hysteresis curve of TS-2
4.3.2 Collaborative work of wood shear walls and
steel frame
In order to study the collaborative work property of
wood and steel, the shear force in the wood shear wall
and the steel frame of TS-2 were calculated. The total
lateral force applied on the specimen P is equal to the
sum of Q1, Q2 and Q3, as shown in Figure 14, while the
shear force in the steel columns Q1 and Q2 can be
obtained from Equation (1) and (2), and the shear force
in the wood shear wall Q3 can be obtained from
Equation (1). The shear force in the steel frame (which
equals Q1+Q2) and the shear force in the wood shear
wall (Q3) can be calculated and are shown in Figure 15
and 16, respectively.
It was found from Figures 13, 15 and 16 that, for the
aspects of cooperative work of the steel frame and wood
shear wall, they roughly maintain their own load bearing
characteristics and show complementary behaviour in
the hybrid system. The shear force P applied on the
specimen was resisted by both steel frames and wood
shear walls, but the percentage of shear force in the two
subsystems changed during the test. Figure 17 gives the
percentage of shear force carried by the two subsystems.
The yield displacement of TS-2 was 30 mm. It was
determined that the shear force was mainly carried by
the wood shear wall before the yield of TS-2. The steel
frame became more active in resisting lateral loads when
Figure 15: Shear force in steel frame (cyclic loading)
Figure 16: Shear force in wood shear wall (cyclic loading)

Figure 17: Percentage of shear resistant force
contributed by wood shear wall and steel frame
Figure 18: Stiffness degradation of timber-steel hybrid
lateral resistant system in cyclic loading
4.3.3 Stiffness degradation
The values of the peak load at each loading circulatings
are listed in Table 6. It was found that the strength of the
specimen began to decrease from the loading step of ±75
mm. The peak load of each loading circle was obtained
from the first loading circulating curve, and the strength
and stiffness degradation could be observed through the
second and third loading circulating curves. According
to Chinese code “Specification of test methods for
earthquake resistant building” in [6], the stiffness of the
timber-steel hybrid lateral resistant system is defined in
Equation (1). The stiffness degradation of the hybrid
system is shown in Figure 18.
Table 6: Peak load at each loading step
Loading Step
±25mm(1/112)
±35mm(1/80)
±45mm(1/60)
±55mm(1/50)
±65mm(1/43)
±75mm(1/37)
±95mm(1/30)
±115mm(1/24)
Circulating
Peak value (kN)
Push Pull
1 81.58 -77.56
2 81.40 -73.23
3 82.08 -72.13
1 102.51 -93.39
2 104.10 -92.97
3 95.37 -88.67
1 117.54 -107.19
2 112.02 -106.42
3 111.60 -101.91
1
2
124.59 -116.75
118.71 -115.29
3 119.13 -122.93
1
2
125.84 -120.14
125.11 -116.03
3 120.35 -119.90
1
2
132.42 -125.55
120.50 -122.50
3 121.91 -120.01
1
2
134.61 -129.65
122.14 -115.95
3 123.09 -102.92
1 114.80 -105.66
2 100.62 -105.27
3 99.46 -102.37
+ Pi
+−Pi
K = (7)
+Δ + −Δ
i
i
where K i = stiffness of the specimen, P i = peak load of
the loading circle “i”, and Δ i = corresponding
displacement to P i .
The stiffness of the hybrid system decreased in the
whole loading process and showed an obvious stiffness
degradation property that is quite similar with that of a
wood shear wall.
5 CONCLUSIONS
This paper studies the lateral performance of a timbersteel
hybrid structure through pseudo static experiments
and focuses on the characteristics of a timber-steel
hybrid lateral resistant system. The conclusions are as
follows:
(1) Failures of nail connections led to damage of the
timber-steel hybrid lateral resistant system. No
failure was found in the wood frame during the
whole period of the test. This was quite different
from the failure modes of the lateral test of single
wood shear walls, which always contained the uplift
failure of studs.
(2) The infill wood shear wall had a great effect on
improving the initial stiffness of the open steel
frame, the initial stiffness increased from 2.18 kN/m
to 5.96 kN/m, more than 2.5 times, after the
installation of the wood shear wall.
(3) The steel frame and the wood shear wall roughly
maintained their own lateral load-bearing
characteristics and show complementary behaviour
in the hybrid system. In the hybrid system, the pinch
effect of load-displacement curve was less
unobvious than that of a wood shear wall, and the
wood shear walls brought a better energy dissipation
property. The percentages of shear force in the steel
frame and wood shear wall changed during the test.
The shear force was mainly carried by the wood
shear wall before the yield of the specimen, and the
steel frame became more active in resisting lateral
i

loads when the wood shear wall went into the plastic
stage.
(4) Strength and stiffness degradation could be
observed through the circulating curves. The
stiffness of the hybrid system decreased throughout
the whole loading process and showed an obvious
stiffness degradation property that is quite similar
with that of a wood shear wall.
ACKNOWLEDGEMENT
The authors gratefully acknowledge the financial support
provided by the Ministry of Science and Technology of
China (National Key Technology R&D Program for the
11th five-year plan of China No. 2008BAJ08B06).
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