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Group Action Factor of Nail Fastener on the Wood Connection With Plywood Sides Plate

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1
Vol. 18 No. 1 April 2011
Tjondro & Rosiman
Abstract
The group action factor was observed in this experimental study. The 18 mm thickness of plywood was used as side’s plate and the main members were made from meranti (shorea sp.) and sengon (paraserianthes falcataria) species. The correlations of group action factor with a number of nails in a row was investigated under uni-axial compression loading test with one to ten nails variation in a row. The member connections with multiple 3 rows with 3, 6, and 9 nails in each row were also tested both under uni-axial compression and tension loading. The group action factor correlated to the number of nails for single row was obtained using the regression analysis. The regression equations presented was group action factor
at the proportional limit (C
gp
), group action factor at the 5% offset diameter (C
g5%
), and group action factor at the ultimate load (C
gu
). The connection strength at 5% offset diameter and proportional limit was closed to the strength design based on the draft of Indonesian Timber Code 2000. The ultimate strength is extremely higher than the design value, giving a sufficient safety factor. Based on this result, a simplified group action factor equation for connection with plywood side’s plate was proposed.
Keywords
:
Group action factor, proportional limit, 5% offset diameter, ultimate load.
Abstrak
Faktor aksi kelompok diteliti dalam studi eksperimental ini.
Plywood
dengan tebal 18 mm digunakan sebagai pelat penyambung sisi dan kayu utama terbuat dari meranti
(shorea sp.)
dan sengon (
paraserianthes
falcataria
). Korelasi antara faktor aksi kelompok dengan jumlah paku dalam satu baris diteliti dari pengujian dengan beban tekan uni-aksial dengan variasi satu sampai dengan sepuluh buah paku. Sambungan dengan 3 baris majemuk dengan 3, 6, dan 9 paku dalam satu baris juga diuji dengan uji beban tekan dan tarik uni-aksial. Faktor aksi ke-lompok yang dikorelasikan dengan jumlah paku untuk satu baris didapat dari analisa regresi. Persamaan- persamaan regresi yang disajikan adalah faktor aksi kelompok pada batas proporsional (C
gp
), faktor aksi kelompok pada 5%
offset diameter
(C
g5%
) dan faktor aksi kelompok pada batas ultimit (C
gu
). Kekuatan sambungan pada 5%
offset diameter
mendekati kekuatan sambungan dari harga disain berdasarkan
draft
Peraturan Kayu Indonesia 2000. Kekuatan ultimit sambungan jauh lebih tinggi dari harga disain, memberikan faktor keamanan yang memadai. Berdasarkan hasil kajian ini, suatu persamaan sederhana untuk perhitungan faktor aksi kelompok dengan pelat penyambung sisi plywood disarankan.
Kata-kata Kunci
:
Faktor aksi kelompok, batas proporsional, 5% offset diameter, beban ultimit.
Group Action Factor of Nail Fastener on the Wood Connection With Plywood Sides Plate
Johannes Adhijoso Tjondro
Civil Engineering Department Parahyangan Catholic University, Bandung, Indonesia Email: tjondro@home.unpar.ac.id, jatjondro@yahoo.com
Evan Kurnia Rosiman
Alumni of Civil Engineering Department Parahyangan Catholic University, Bandung, Indonesia
ISSN 0853-2982
JurnalTeoretis dan Terapan Bidang Rekayasa Sipil JurnalTeoretis dan Terapan Bidang Rekayasa Sipil
1. Introduction
The connection failure modes may depend on the properties of wood main member, wood side plate and nail. Several failure modes may occur as shown in
Figure 1
. There are six failure modes possible for single shear and four failure modes for double shear connections, Soltis 1999. The connection design strength due to axial load of single nail was different from the strength of a group of nails because the force was not distributed uniformly in each nail. The purpose of this experimental study was to observe the group action factor, the failure behavior and the strength of the connections. The 18 mm thickness of plywood was used as a connection side’s plate and main members were made from
meranti
and
sengon
species. The correlation of group action factor with a number of nails in a row was investigated under uni-axial compression test with one to ten nails varia-tion in a row for total of 60 specimens. The 36 member connection specimens using three rows with 3, 6, and 9 nails in every row were also made for compression and tension tests.
2
Jurnal Teknik Sipil
Group Action Factor of Nail Fastener on the Wood Connection ...
The basic nail strength for different yield modes in the draft of Indonesian Timber Code (SNI-03-xxxx-2000) which is adopted from NDS (AWC, 2005) may be calculated by
Equations (1)
to
(6)
. The experimental result of the multiple nail connections was compared to this design value to evaluate the group action factor. In the NDS 2005, besides number of nail; type of fastener, ratio of the axial stiffness of wood and side’s plate, slip modulus between the main member and side’s plates and spacing of the fastener were needed to determine the value of C
g
. In this experimental study, the complicated equation of C
g
in NDS 2005 for wood connection with plywood sides plate is going to be sim- plified based on number of nails. The single nail strength at possible failure modes are: where: N = yield strength (N) K
D
= 2,2 for D
≤
4.3 mm, 0.38D + 0.56 for 4.3 mm < D < 6.4 mm, 3.0 for D
≥
6.4 mm. F
em
= main member dowel bearing strength (MPa), F
e
= 16600 G
1.84
(psi) F
es
= side member dowel bearing strength (MPa) F
yb
= dowel bending yield strength (MPa)
Figure 1. Yield modes on the connections (a) single shear (b) double shear
Source: Soltis (1999)
mode I
s
: N
Is
=
Dess
KF3,3Dt
(1) mode III
m
:
N
IIIm
=
Deem1
K)R21(
DpFk3,3
(2) k
1
=
2em2eybe
pF3D)R21(F2
)R1(21
(3) mode IIIs: N
IIIs
=
)R2(K
FDtk3,3
eDems2
(4) k
2
=
2sem2eybee
tF3D)R21(F2
R)R1(
21
(5) mode IV:
N
IV
=
)R1(3
FF2KD3,3
eybemD2
(6) R
e
= F
em
/F
es
t
s
= side member thickness (mm) D = nail diameter (mm) p = nail penetration depth (mm) The design of single nail strength
N calculated by
Equations (1)
to
(6)
. The wood and plywood proper-ties to calculate single nail strength was based on the material properties test results as was shown in
Table 1
. And the design of adjusted single nail strength
Z’
calculated by
Equation (7)
. Where:
Z’
= adjusted design strength (
N
)
C
M
= wet service factor
C
t
= temperature factor
C
pt
= preservation factor
C
rt
= fire resistance factor
C
d
= penetration depth factor
C
di
= diaphragm factor
C
eg
= end grain factor
C
tn
= toe-nail factor All C factors was assumed to be 1.0 except for
C
d
and the design of connection strength
Z
calculated by
Equation (8).
where
Z
= design of connection strength (N) n = total number of nail
z
= resistance factor = 0.65
2. Method and Materials
This research based on the theoretical and experi-mental studies. The materials were tested based on the ASTM D143-94 standard testing for small clear speci-men, ASTM 2005. The main member of the specimen was designed using
sengon
species which has lower specific gravity (G) than plywood, and
meranti
species which have higher specific gravity as shown in
Table 1
. The single row specimen was tested under uni-axial compression loading and the multiple rows connection was tested both under uni-axial compression and tension loadings.
tnegdidrtpttM
CCCCCCCNC'Z
(7)
'ZnZ
Z
(8)
3
Vol. 18 No. 1 April 2011
Tjondro & Rosiman
Based on the material properties in
Table 1
and
Equa-tions (1)
to
(6)
, the design strength of a single nail was calculated. The result was then presented in
Table 2
. It was shown that the critical failure mode for
sengon
with lower specific gravity than plywood was mode IlI
m
and for
meranti
with higher specific gravity than ply-wood was mode IV. The design strength of the connec-tions with multiple nails was as shown in
Table 3
.
Material
G
F
c//
(MPa)
F
t//
(MPa)
mc (%)
Sengon 36x60
0.29
20.65
52.33
12
Meranti 32x70
0.49
45.07
86.63
12
Plywood 18x60
0.38
22.19
52.11
12
Nail
diameter= 2mm
length= 40mm
F
yb
=(130.4 – 214 d)1000 (psi)
*)
Table 1. Average value of material data
*) NDS 2005 G = specific gravity, Fc// = compression strength parallel to the grain, Ft// = tension strength parallel to the grain, mc = moisture content Source: Rosiman (2007)
Type
Yield Mode
Yield strength (
N
)
Adjusted nail strength
*)
(
N
)
Sengon-
plywood I
s
1 247.000 330.478 III
m
360.521
**)
III
s
417.908 IV 382.325
Meranti-
plywood I
s
1 247.000 456.438 III
m
707.612 III
s
531.712 IV
497.932
**)
Table 2. Adjusted single nail design strength
*) including C
d ,
**) critical value, predicted failure mode Source: Rosiman
(2007)
Type
n
Connection strength Z
*)
(kN)
Sengon-
plywood
2 x 9 = 18
3.867
2 x 18 = 36
7.733
2 x 27 = 54
11.600
Meranti-
plywood
2 x 9 = 18
5.340
2 x 18 = 36
10.681
2 x 27 = 54
16.021
Table 3. The design of connection strengt
*) including
z
, without C
g
Source:
Rosiman (2007)
The variation of number of row and nails in one row on the specimens was shown as in Appendices, from
Figure A
to
D
and the experimental settings for three rows compression test and three rows tension test were described in
Figures 2a
and
2b
. The test was done under displacement control at 0.6 mm per minute rate using universal testing machine.
Figure 2. Experimental settings (a) three rows compression test, (b) three rows tension test
(a) (b)
3. Results and Discussion
3.1 The group action factor
The investigation was made to the group action factor at different level of strength, such as at proportional limit (C
gp
), 5% offset nail diameter (C
g5%
) and ultimate (C
gu
) as described in
Figure 3
. The compression tests result for single row was shown as in
Table 4
and
Figures 4
and
5
. The C
g
data for regression analysis was generated from the multiple nail strength divided by n times of single nail strength. Although the data were scattered and have a low R
2
, the result of C
g
at different level of strength was close. The result for three rows connection was shown as in
Table 5
and
Figures 6, 7
and
8
. The result of C
g
at compression test at proportional limit was lower than tension test, but the opposite result was occurred for C
g5%
and C
gu
at three rows test. Although the data of three row test were scattered but the R
2
was higher than single row test.
4
Jurnal Teknik Sipil
Group Action Factor of Nail Fastener on the Wood Connection ...
Figure 4. Group action factor of one row
sengon
-plywood nail connection Figure 5. Group action factor of one row
meranti
-plywood nail connection
Specimen
Force
Equations
*)
R
2
Sengon
-plywood P
bp
C
gp
= 0.906 e
-0.02n
0.13 P
5%
C
g5%
= 0.863e
-0.01n
0.23 P
ult
C
gu
= 0.912 e
-0.01n
0.13
Meranti
- plywood P
bp
C
gp
= 0.898 e
-0.02n
0.18 P
5%
C
g5%
= 0.921e
-0.02n
0.14 P
ult
C
gu
= 0.920 e
-0.02n
0.19
Table 4. Group action factor for single row
*) without outlier
Specimen
Force
Equations
*)
R
2
Compression (-) P
bp
C
gp
= 0.989 e
-0.03n
0.56 P
5%
C
g5%
= 1.020 e
-0.02n
0.57 P
ult
C
gu
= 0.959 e
-0.01n
0.28 Tension (+) P
bp
C
gp
= 1.023 e
-0.03n
0.67 P
5%
C
g5%
= 0.995 e
-0.02n
0.54 P
ult
C
gu
= 0.938 e
-0.02n
0.31
Table 5. Group action factor for three rows
*) without outlier
Figure 3. Typical load vs deflection curve of the connection
P
bp
P
5%
P
ult
displacement (mm) Load (kN)
5
Vol. 18 No. 1 April 2011
Tjondro & Rosiman
Based on the single and multiple rows tests, the pro- posed conservative simplified group action factor C
g
= e
-0.03(n-1)
based on C
g
=1 for n =1, and C
g
= 0.76 for n=10 which is
observed manually
may be used for design connection with plywood sides plate.
3.2 The strength of connections
The comparison of the experimental strength to the design value was done for both types of specimen as shown in
Figures 9
and
10
. The result showed that the strength at proportional limit and 5% offset was lower than the design value. It means that without considering C
g
the connection will exceed the elastic limit under design load. But the ultimate strength could achieve 2.5 to 3.0 times the design value as was shown in appen-dices
Table A
and
Table B
, giving a significant safety factor to prevent collapse.
Figure 6. Group action factor of three row nail connection at the proportional limit Figure 7. Group action factor of three row nail connection at the 5% offset nail diameter Figure 8. Group action factor of three row nail connection at the ultimate strength
3.3 The failure modes
The Failure modes on
sengon
connection with lower specific gravity than plywood was mode IlI
m
and for
meranti
connection with higher specific gravity than plywood was mode IV, match with the value prediction in
Table 2
.
Figure 9. Ratio of experimental to design strength of
sengon
-plywood connection

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