第一工業大学研究報告第26号（2014）pp.79－86

791
第一工業大学研究報告
第 26 号(2014)pp.??-??

EARTHQUAKE RESPONSE ESTIMATION OF WOODEN
HOUSE WITH NEW BRACE FASTENER
EARTHQUAKE RESPONSE ESTIMATION OF WOODEN
HOUSE WITH Tomoki
NEWFURUTA
BRACE FASTENER
Tomoki FURUTA

Professor, Dept. of Architecture and Design, Daiichi Univ. Institute of Technology(Kokubu-Chuo 1-10-2, Kirishima-shi, Kagoshima-ken 899-4395, Japan)
E-mail: t-furuta@daiichi-koudai.ac.jp

Abstract: A new type brace fastener which fastens the end of a diagonal wood brace to the end of column isdeveloped for Post and Beam construction wooden houses. Since the brace fastener contains high damping rubber,it absorbs a displacement between the end of a wood brace and a column, damage of wood around wood screws isable to be prevented. On shake table test of a wood frame with a double wood brace fastened by the new brace
fasteners, the new brace fastener showed higher seismic performance in comparison with normal brace fastenerespecially under large earthquake motion. Moreover, by means of earthquake response analysis of two-storied
wooden house, it was confirmed that the new brace fastener showed good seismic performance.
Keywords: Wooden house, Brace fastener, High damping rubber, Shake table test, Earthquake response analysis

1 INTRODUCTION
Wooden houses play an important role to preserve
human life and property. They need to bear repeatedlarge earthquakes and to be in use even after large
earthquakes. However, once wood is subjected to aforce, a decline of stiffness occurs. Therefore, shear
stiffness of shear walls subjected to an earthquake isconsidered to decline, which means wooden houses
are hard to resist the repeated large earthquakes.
From the expressed reason, authors have beendeveloped a new brace fastener which fastens the endof a diagonal wood brace to the end of column for
Post and Beam construction wooden houses [1, 2].
Since the brace fastener contains high damping rubber,it absorbs a displacement between the end of a woodbrace and a column, damage of wood around woodscrews is able to be prevented. Therefore, the brace
fastener minimizes the decline of stiffness, moreover
damping force by the high damping rubber is
produced.
In this paper, to evaluate basic performance of the new
type brace fastener, shake table test of a wood framewith a double wood brace fastened by the new brace
fasteners was conducted firstly. Secondly, using theresult of the shake table test, earthquake response
analysis of two-storied wooden house was conducted
to evaluate the performance of the new brace fastenerin ordinary Post and Beam wooden houses. The
seismic performance of the new brace fastenerpresented in this paper is authorized officially,
therefore it is able to be used under the BuildingStandard Law in Japan.

2 OUTLINE OF THE NEW BRACEFASTENER
The new type brace fastener, as shown in Figure 1,
consists of a L-shaped steel normal brace fastener, asteel plate and a high damping rubber with 5mm thick.
The high damping rubber glues a L-shaped normalbrace fastener and a steel plate together. The L-shaped
normal brace fastener is fastened to the end of acolumn with nine 75mm long wood screws and thesteel plate is fastened to the end of a wood brace withsix 45mm long wood screws. In addition to the woodscrews, four 45mm long wood screws which fasten
the L-shaped fastener and a wood brace directly areadded for fail-safe considering exfoliate of highdamping rubber. Picture 1 shows a wood frame with adouble wood brace which is fastened by the new brace
fasteners at the ends of braces as shown in Picture 2.

3 SHAKE TABLE TEST
Shake table test of a wood frame specimen with a

第一工業大学研究報告

80

double wood brace fastened by the new brace
fasteners was performed to evaluate its seismic
performance. Figure 2 shows a wood frame for shake
table test. A double wood brace, whose cross section is
90mm x 45mm, was fastened by the new brace
fasteners at the both ends. Wood species of column,
sill and brace of the specimen was Tsuga heterophylla
and beam was Dugrus fur. Since two weights on the
top of the specimen were approximately 20kN in total,
whole weight of the upper half of the specimen was
24.5kN.
10%, 30% and 50% of JMA Kobe wave (earthquake
motion observed at Kobe branch of Japan
Meteorological Agency in January 17th in 1995) were
input to the specimen in one direction. Before starting
the test, to have the natural period and the damping
ratio, small random wave and impulse wave were
input to the specimen. Table 1 shows natural periods
and damping ratios calculated from the result of 3mm
impulse wave. While there is no difference in natural
period between the case with the new brace fasteners
and the one with normal brace fasteners, damping
ratio in the case with the new brace fasteners washigher than the one with normal fasteners.
45mm
120

mm

2

Picture 2: New brace fastener installed at theend of a brace(Unit : mm)

Excitation direction

Wood brace is installedin this plane
WeightBeam(105x180,Douglas fir)
Column(105x105,Tsuga heterophylla)

Steel braceSill(105x105,Tsuga heterophylla)

Figure 2: Wood frame for shake table test
Table 1: Natural period and damping ratio

Steel plate

147mm

Fail-safe
wood screw
High damping
rubberStandard
wood screw
Wood brace
L-shaped fastener

第26号（2014）

Sill

Figure 1: New developed brace fastener

Double wood bracewith the new brace fasteners
Double wood bracewith normal brace fasteners

Natural period(sec)Damping ratio
(%)

0.341

9.5

0.343

6.2

Figure 3 and Figure 4 show relationships between
shear force and story drift of the specimen with adouble wood brace fastened by the new brace
fasteners and normal brace fasteners respectively.
The tendency of the result of the case with the newbrace fastener and the one with normal brace fasteneris almost the same under 10% and 30% of JMA Kobe
wave. However, in the case of 50% of JMA Kobe
wave, while maximum story drift of the specimen
with the new brace fasteners was 3.0%, the one withnormal brace fasteners was 5.6%, so it is 1.9 times asmuch as the drift with the new brace fasteners.
Slight deformation of the new brace fastener wasobserved after the 50% of JMA Kobe excitation,
however, in the case of normal brace fastener, sprit of
the fastener, pull out of wood screws and buckling of awood brace occurred.

Picture 1: Wood brace fastened by the newfastener

Figure 5 shows maximum drift of the case with the
new brace fastener and the one with normal fastener.
In the cases under 10% and 30% of JMA Kobe wave,
the maximum drifts of the two cases were almost theFURUTA：EARTHQUAKE RESPONSE ESTIMATION OF WOODEN HOUSE WITH NEW BRACE FASTENER-20

Shear force (kN)

-2

0

2

4
Drift (%)

JMA Kobe 10%
New fastener-6

Shear force (kN)

-2

0

2

4

6
Drift (%)

JMA Kobe 30%
New fastener
-6

-4

-2

JMA Kobe 10%
Normal fastener

10
5
0

0

2

4

2

4

6
Drift (%)

JMA Kobe 50%
New fastener

Figure 3: Shear force-drift relationship withdouble wood brace fastened by the new brace
fasteners

6

Drift (%)

JMAJMA Kobe
Kobe 30%
30%
NormalNormal fastenerfastener

15
10
5
0

-15
0

6

15

-10

5

-15

4

0

2

4

-5

10

-10

2

Drift (%)

-15

15

-5

0

-10

5

-15

-2

-4

10

-10

-4

0

-5

-5

-6

6

15

0

5

-15

-15

0

10

-10

5

-10

-4

Shear force (kN)

10

Drift (%)

JMA Kobe 50%
Normal fastener

Figure 4: Shear force-drift relationship withdouble wood brace fastened by normal brace
fasteners

6
5With t he new fastenerWith normal fast ener

4
3
2
1
0
10%

3

15

-5

-5

-6

-2

Shear force (kN)

-4

15

-4

Shear force (kN)-6

-6

Maximum drift (%)

Shear force (kN)same. Therefore, the use of the new brace fastener iseffective especially under relatively large earthquake
motion.

81

30%

50%

Intensity of JMA Kobe wave

Figure 5: Maximum drifts of the specimen withdouble brace under 10%, 30% and 50% of JMA
Kobe wave

6

第一工業大学研究報告

82第26号（2014）

Earthquake response analysis of two-storied wooden
houses was carried out to examine the seismic
performance of the new brace fastener underearthquake motions.

Non-liner spring(Nailed plywood)

910mm 910mm

Figure 6: Analysis model of two-storied wooden
house

5
2

4

6

8

Drift (%)

-10

New fastener-15(a) Double wood brace with the new brace fasteners
Shear Force
kN)

15
10
5

0
-8 -6 -4 -2 0
-5
-10

2

4

6 8
Drift (%)

Normal fastener-15(b) Double wood brace with normal brace fasteners
15

Shear Force
(kN)
-8

-6

-4

10
5
0
-2 0
-5
-10
-15

2

4

6

8

Drift (%)
Nailed Plywood(c) Nailed plywood
Figure 7: Hysteresis model of shear walls

Drift (%)

Non-liner spring(Wood braces)

2730mmLumped mass

2730mmFigure 8 and Figure 9 shows time histories of story
drift and shear force of the cases with the new brace
fastener and with normal brace fastener respectively.
Comparing the result of shake table test to the one ofearthquake response analysis under 50% of JMA Kobe
wave, there is good agreement between them. For thecase of normal brace fastener, because there wasserious damage to fasteners and wood braces, a miner
disagreement exists. Analysis result under 30% of
JMA Kobe as shown in Figure 10 shows good
agreement with the shake table test result.
Consequently, it is considered that the analysis models
of a wood frame with the new brace fastener andnormal brace fastener presented here are adequate forthe use of evaluating earthquake response of wooden
houses.

100-8 -6 -4 -2 0
-5

Shear force (kN)

Figure 6 shows analysis model of a two-storied
wooden house. The non-linear diagonal springs in themodel represent double wood brace and nailed
plywood. Figure 7(a) shows the hysteresis model of
double wood brace with the new brace fasteners
which was calibrated by the shake table test results. A
wood frame with double wood brace fastened bynormal brace fasteners was also modelled as shown in
Figure 7(b). Figure 7(c) shows the one of nailed
plywood. NCL model [3] was adopted for the
non-linear diagonal spring.

15

Shear Force(kN)

4 EARTHQUAKE RESPONSEANALYSIS

4

3 New Fastener
2
1
0
-1 10
-2
-3

15 New Fastener
10
5
0
-5 10
-10
-15

Experiment
Analysis

20

30
(sec)

Experiment
Analysis

20

30
(sec)

Figure 8: Time history of the case with the newbrace fasteners under 50% of JMA Kobe wave

83

FURUTA：EARTHQUAKE RESPONSE ESTIMATION OF WOODEN HOUSE WITH NEW BRACE FASTENER

Experiment
Analysis

15 Normal fastener
10
5
0
20
-5 10
-10
-15

Experiment
Analysis

Shear force (kN)

Drift (%)

6 Normal Fastener
4
2
0
20
-2 10
-4
-6

Weight of the first floor(W1) and the one of the second
floor(W2) of analysis models were calculated by
Equation (1), (2) and (3).

30
(sec)

30
(sec)

Experiment
Analysis

Drift (%)

Normal Fastener
1.5
1.0
0.5
0.0
20
-0.5 10-1.0-1.5

Shear force (kN)

Figure 9: Time history of the case with normalbrace fasteners under 50% of JMA Kobe wave

15 Normal fastener
10
5
0
20
-5 10
-10
-15

Experiment
Analysis

30
(sec)

30
(sec)

Figure 10: Time history of the case with normalbrace fasteners under 30% of JMA Kobe wave

5

W = 0.667 • Qa / C0 / Re

(1)

W1 = W / ( 1 + Rm • Rf )(2)

W2 = W - W1

(3)

where W is weight of whole analysis model of a
two-storied wooden house(= W1+W2). It is assumed
that 33% of shear force which affects a wooden houseis carried by non-structural members, so 0.667 ismultiplied in Equation (1). Qa is an allowable shear
strength of a double wood brace on the firstfloor(=7.13kN), C0 is ratio of required shear force tothe weight of a building at damage limit (=0.2), Re isratio of existing wall length to required wall length,
Rm is ratio of weight of unit area on the second floor tothe one on the first floor(defined as 0.7 in this study),
Rf is ratio of the second floor area to the first floor
area. In Building Standard Law in Japan, Qa of shear
walls and C0 for wooden houses are defined as above.
Natural period of the analysis model of Rf=1.0 in thecase of Re=1.0 and is 0.37 sec, the one of Re=2.0 is
0.26sec.
Input earthquake waves to the analysis models wereJMA Kobe which was scaled down to 55% and BCJ
L2(Level 2 simulated earthquake wave for structuraldesign by The Building Center of Japan). Figure 11
shows the response spectra of the two earthquake
waves. Damping ratio of 5% was given to the all
analysis models.
Table 2: Analysis cases
Shear wall
Double wood bracewith the new brace fasteners
Double wood bracewith normal brace fasteners
Nailed plywood

Ratio of existing wall
length to required wall
length (R e )
1.00
1.25
1.50
1.75
2.00

Ratio of the second
floor area to the firstfloor area (R f )
1.25
1.00
0.75
0.50

For the analysis model, five ratios of existing wall
length to required wall length(Re) in the BuildingStandard Law in Japan were set as shown in Table 2.
Moreover, four ratios of second floor area to first floorarea(Rf) were also considered to the analysis model.
As for extra cases, The analysis model with both adouble wood brace and a nailed plywood as well as
the one which has twice wall length on second floor
were also build and analysed. A double wood brace
was arranged on the first floor and lumped masses at
every node and wall length on the second floor were
adjusted to meet the corresponding Re and Rf.

Responce acc. (gal)

1500
1000
500
0

JMA Kobe 55%
BCJ L2
0

0.2

0.4
0.6
0.8
Natural period (sec)Figure 11: Response spectra (h=5%)1

第一工業大学研究報告

84

Figure 12 shows maximum response story drift in thecase of JMA Kobe wave. The response tends todecreases as Re increases. It is also found thatmaximum response drifts of the cases with the newbrace fastener are conservative in comparison with theones fastened by normal brace fastener at any Res andRfs. At Re=1.0, while drifts of the cases with normal
fastener are almost over 3%, the ones with the newbrace fastener are generally less than 2%.
New fastener, 1st floor
Normal fastener, 1st floor

1.0

1.5
Re

2

1.0

1.5
Re

4
2

1.5
Re

6

Drift (%)

2

1.5
Re

2.0

Figure 12: Maximum response drift of two-storied
analysis model under JMA Kobe wave

2.0

Rf =1.0

2

1.0

1.5
Re

2.0

Rf =0.75

4
2

1.0

1.5
Re

6

Rf =0.5

1.0

1.5
Re

4

0

2.0

4

0

1.0

6

Rf =0.75

1.0

2

0

2.0

Drift (%)

Drift (%)

6

Rf =1.25

6

Rf =1.0

New fastener, 2nd floor
Normal fastener, 2nd floor

4

0

2.0

4

0

6

Drift (%)

Drift (%)

60

New fastener, 1st floor
Normal fastener, 1st floor

Rf =1.25

20Drift (%)

New fastener, 2nd floor
Normal fastener, 2nd floor

4

6

Figure 13 shows the case of BCJ L2 wave. There is asame tendency as the case of JMA Kobe wave. It isfound that drifts of second floor with normal fastenerare generally over 3% and the ones with the new brace
fastener are also less than 2% at Re=1.0. Since drift
where maximum shear force of the restoring force of
the analysis model reaches is 1.8%, the use of the newbrace fastener is considered to be able to keep story
drift approximately below 2%.

Drift (%)

Drift (%)

6第26号（2014）

2.0

Rf =0.5

4
2
0

1.0

1.5
Re

2.0

Figure 13: Maximum response drift of two-storied
analysis model under BCJ L2 wave

Figure 14 shows the case of analysis with double
wood brace together with nailed plywood. In this case,a half of allowable shear strength of the analysis
model is occupied by nailed plywood whose unit
allowable shear strength is 4.46 kN. In the case ofanalysis model with normal brace fastener, story drift
decreased remarkably by replacing a half of bracingwith nailed plywood especially in lower Re cases. In
the other case with the new brace fastener, there is nomuch difference between the case with wood brace
only and the one with wood brace and nailed plywood.
The reason is considered that actual seismic
performance per allowable shear strength of a double
wood brace with the new brace fastener is equivalent
to a nailed plywood and much higher than the one
with normal brace fastener as shown in Figure 15.
Figure 16 is result of analysis model which has twice
Re on second floor as much as the one on first floor.
While the response drift on the second floor in thiscase decreased compared with the case of same Re on
first and second floor, the one on the first floor
increased. The response drift on the first floor withnormal brace faster is 6.1%, and the one with newbrace fastener is 2.5%.

Shear force per allowable strength

FURUTA：EARTHQUAKE RESPONSE ESTIMATION OF WOODEN HOUSE WITH NEW BRACE FASTENER

Drift (%)

2.5
2.0
1.5
1.0
0.5
0.0

0

2

4
Drift (%)

Rf =0.75
Bracing 50%
Nailed plywood 50%

4
2
0

1.0

1.5
Re

2.0

Figure 14: Maximum response drift of two-storied
analysis model with double wood brace andnailed plywood under JMA Kobe wave

6

8

Figure 15: Shear force per allowable shear
strength of shear walls

New fastener, 1st floor
Normal fastener, 1st floor

Drift (%)

6

New fastener, 2nd floor
Normal fastener, 2nd floor

7

Nailed plywood
Double wood brace with normal fasteners
Double wood brace with the new fasteners

New fastener, 2nd floor
Normal fastener, 2nd floor

6
New fastener, 1st floor
Normal fastener, 1st floor85

Rf =0.75
Re2/Re1=2

4
2
0

1.0

1.5
Re1

2.0

Figure 16: Maximum response drift of two-storied
analysis model with twice Re on second floor
under JMA Kobe wave (Re1 : Re on first floor,
Re2 : Re on second floor)

5 CONCLUSIONS
A new type brace fastener which fastens the end of adiagonal wood brace to the end of a column isdeveloped for Post and Beam construction wooden
houses.
On shake table test of a wood frame specimen with adouble wood brace fastened by the new brace
fasteners, while maximum story drift was 3%, the one
with normal brace fasteners was 5.6% under 50% of
JMA Kobe wave. On the tests under 10% and 30% of
JMA Kobe wave, the maximum story drifts of the twocases, namely with the new fastener and with normal
fastener, were almost the same. Therefore, it was
found that the use of the new brace fastener is

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第一工業大学研究報告

effective especially under relatively large earthquake
motion.
Moreover, by means of earthquake response analysis
of various two-storied wooden houses, it was
confirmed that the new brace fastener showed goodseismic performance. Even if story drift is estimatedto be relatively large with normal brace fastener, theuse of the new brace fastener is considered to be able
to keep story drift approximately below 2%.
Through the above considerations, it was also foundthat actual seismic performance per allowable shear
strength of a double wood brace with the new brace
fastener is equivalent to a nailed plywood and muchhigher than the one with normal brace fastener.
REFERENCES[1] Furuta, T. and NAKAO, M. : The Evaluation of aDamper Device with High Damping Rubber for
Wooden Houses, ATC & SEI 2009 Conference on
Improving the Seismic Performance of Existing
Buildings and Other Structures, No.1046, 2009[2] Furuta, T. and Nakao, M. : The Evaluation of a
Simple Damper Device with High Damping
Rubber for Wooden Houses, 14th European
Conference on Earthquake Engineering, No.1216,
2010[3] Matsunaga, H., Miyazu, Y. and Soda, S. : A
Universal Modeling Method for Wooden
Shear/Nonshear Walls, Journal of Structural andConstruction Engineering 74: 639, 889-896, 2009
(in Japanese)

第26号（2014）8