STRUCTURAL PERFORMANCE EVALUATION OF WOODEN
FRAMEWORK WITH JOINTED COLUMN
Kota Iinuma1, Masato Nakao2
1 INTRODUCTION 123
Many of traditional wooden buildings have been built on
foundation stones(Soseki). Therefore, their bottom ends of
columns rotted or had damage by termites as time goes on.
Netsugi, a traditional maintenance technique replacing
such a rotted or damaged part of the bottom of column
with a new member, had been done since long ago. There
are various forms of joint of a new member and old one,
and KANAWATSUGI joint is generally adopted for
Netsugi from among many joint methods. It is quite likely
that the structural performance of jointed column is worse
than the one of a column without joints. Though many
studies on traditional type joint itself have been conducted,
there have been few examinations of a column with a joint.
As for a column, bending moment produced by shear wall
and compressive axial force due to dead load affects the
joint of columns within a framework so it is difficult to
evaluate the structural performance of the framework with
the jointed column from only test results of the joint itself.
Therefore, test specimens of framework with a jointed
column were prepared and static shear loading tests were
conducted to comprehend the structural performance. It
can be considered that KANAWATSUGI joint has
different structural performance by loading direction. Tests
of the two frameworks, one had a joint in strong axis and
the other had in weak axis, were conducted. And a
comparison of the structural performance of the two
frameworks and the one without joint was made.
2 SPECIMENS AND TEST METHODS
Fig. 1 shows the test a specimen of framework. Shear walls
in traditional wooden buildings are usually mud plastered
walls but on this study nailed plywood is used to the
framework instead of mud plastered wall. It is installed
easily and carries shear force which affect the joint. Fig. 2
shows details of the KANAWATSUGI joint which is
1
Kota Iinuma, Graduate School of Urban Innovation, Yokohama
National University, 79-5, Tokiwadai, Hodogaya-ku, Yokohama,
Kanagawa, Japan. 240-8501 Email: [email protected]
2
Masato Nakao, Institute of Urban Innovation, Yokohama
National University, Email: [email protected]
located in the lower part of one column. The other column
has no joint to compare. Specimens are 2 types, KN-1 and
KN-2. KN-1 has a joint in strong axis direction and KN-2
has the one in weak axis direction against affected bending
moment. The position and the size of the joint were
examined through measuring survey of existing traditional
wooden buildings.
Positive-negative lateral repeated force was applied to the
beam of specimen. The lateral load was repeated at
deformation angles of 1/300, 1/150, 1/100, 1/75, 1/50, 1/30,
1/20 and 1/15rad. Approximately 20 kN of weight as dead
and live load was loaded on the beam of the specimen.
Figure 1: Framework specimen
Figure 2: Detail of joint
3 RESULTS AND DISCCUSION
Table 1 shows test results and Fig.3 shows loaddisplacement relationship of specimen KN-1 and KN-2.
Fig.4 shows KN-2 specimen at ultimate state. In the
specimen KN-1, during the positive side loading the load
reached the maximum in 1/20 rad of deformation angle.
Then bending failure occurred on Ashigatame(lateral
member which connects columns at lower position) in 1/15
rad though columns were not damaged seriously. When the
negative side loading, tenon at the end of Ashigatame was
broken and the load decreased in 1/30 rad. However,
Kanawatsugi joint had no damage even in 1/20 rad of
deformation angle. The maximum load on the negative
side loading was 12.5kN and it was on the same level as
the positive side 12.9kN. In the specimen KN-2, the
maximum load and stiffness on the positive side were
Table 1: Tests Results
Specim ens
KN -1
Load(kN)
KN -2
un-jointed o n positive
jointed o n n egative
un-jointed o n positive
jointed o n n egative
Stiffness
(kN /rad.)
761.8
824.4
984.6
840.4
Pm ax. M ax.D isp.
(kN )
(rad.)
12.9
1/15
12.5
1/20
15.2
1/20
13.4
1/28
20
15
10
5
0
-­‐80
-­‐60
-­‐40
-­‐20 -­‐5 0
-­‐10
-­‐15
20
40
60
80
Deformation angle
(×1/1000rad.)
KN-­‐1
KN-­‐2
( 20
Figure 3: Load-displacement relationship of specimens
which has no relation to the existence of the joint. The
specimen KN-2 has similar tendency to KN-1 that bending
moment at the upper or lower part of the joint increase as
deformation angle increases.
In jointed columns within the specimen KN-1 and KN-2,
bending moment at the lower part of the joint was low
when especially deformation angle is relatively large. This
is because the negative bending moment applied from
Ashigatame cancelled the existed positive bending moment.
Bending moment at Ashigatame was especially large in
1/30 rad or more of deformation angle, so bending moment
at the lower part of the joint was low.
Horizontal displacement of jointed column in negative side
loading was larger than that of column without the joint in
the positive side loading. Horizontal displacement of
jointed column within the specimen KN-2 was larger than
that of KN-1. Thus it can be recognized that bending
rigidity varies by the existence of the joint and the
direction of the joint.
1/300
1/150
1/100
1/75
1/50
1/30
1/20
Joint
3000
2500
2000
1500
1000
Height(mm)
higher than the ones of the specimen KN-1. The load on
the negative side reached the maximum in 1/30 rad, then
split occurred on the tenon of Ashigatame along the peg in
1/28 rad. Deformation performance on the negative side
loading of the specimen KN-2 was lower than that of KN-1,
but the maximum load of KN-2 was higher than that of
KN-1 by 10percent. From these test results, it was found
that the difference in loading direction of Kanawatsugi
joint as follows; the maximum load of KN-2 is higher than
that of KN-1 and the maximum deformation angle of KN-2
is over 1/30 rad and KN-1 has better deformation
performance.
500
0
1.5
0.5
-­‐0.5
Bending Moment(kNm)
Figure 5: Bending moment of jointed column within KN-1
specimen on the negative side
2.5
4 CONCLUSIONS
Figure 4: KN-2 specimen at ultimate state
Fig. 5 shows bending moment distribution of the jointed
column within the specimen KN-1 on the negative side
loading. Vertical axis indicates the height of 4 measured
points by strain gauges, namely the top end of column, the
upper part of the joint, the lower part of the joint and the
bottom end of column. Bending moment at the upper or
lower part of the joint was higher than that at the top end
of column or the bottom end of column. Bending moment
has a tendency to increase as deformation angle increases,
On this study, static shear loading tests of the frameworks
with jointed column were conducted. The follwing were
the main findings:
1. When lateral force is applied in strong axis direction,
the maximum load of the jointed column is a little
lower than that of column without joint and
deformation performance of the jointed column is on
the same level as the column without joint. In weak
axis direction, the maximum load of the jointed
column is on the same level as the column without
joint and deformation performance of the jointed
column is worse than that of the column without joint.
2. Bending moment at column is higher as the
deformation angle is larger. When the angle is in 1/30
rad or more, bending moment at the lower part of the
joint decrease because of bending moment at
Ashigatame.
3. Bending rigidity of jointed column is lower than that
of column without joint. Bending rigidity of
Kanawatsugi joint in weak axis direction is lower
than the one in strong axis direction.