BENDING AND BONDING PROPERTIES OF MIXED-SPECIES GLUED LAMINATED TIMBER FROM MERPAUH, JELUTONG AND SESENDOK

Abstract

This study investigates the bending and bonding performances of glued laminated timber beams manufactured using a combination of Malaysian lower and higher- grade timber species. Two types of beams were prepared which were mono-species and mixed-species glulam. Mono-species glulam with uniform layup were fabricated using Merpauh, Jelutong and Sesendok. Mixed-species glulam with balanced layup were fabricated whereby Merpauh was positioned equally at the outer layers and either Jelutong or Sesendok were positioned at the inner layers. Three replicates of ten-layered glulam beams measuring 100 mm in width, 300 mm in depth and 6200 mm in length were manufactured according to MS758 for each mono and mixed-species glulam. Bending, delamination and block shear tests were done on all the glulam beams. The results show that glulam manufactured from the combination of Sesendok and Merpauh obtained the highest bending properties and structural efficiency. In addition, the bonding performance at the interface between Sesendok-Merpauh lamellas proved to be excellent.

Full text

81:4 (2019) 165–170 | www.jurnalteknologi.utm.my | eISSN 2180–3722 |DOI: https://doi.org/10.11113/jt.v81.12557|
Jurnal
Teknologi
Full Paper
BENDING AND BONDING PROPERTIES OF
MIXED-SPECIES GLUED LAMINATED TIMBER
FROM MERPAUH, JELUTONG AND
SESENDOK
Wan Hazira Wan Mohamada, Norshariza Mohamad Bhkarib,
Zakiah Ahmadb*
aFaculty of Applied Sciences, Universiti Teknologi MARA
Malaysia, 40450 Shah Alam, Selangor, Malaysia
bFaculty of Civil Engineering, Universiti Teknologi MARA
Malaysia, 40450 Shah Alam, Selangor, Malaysia
Article history
Received
12 March 2018
Received in revised form
16 January 2019
Accepted
15 May 2019
Published online
25 June 2019
*Corresponding author
zakiah@salam.uitm.edu.my
Graphical abstract
Abstract
This study investigates the bending and bonding performances of glued laminated
timber beams manufactured using a combination of Malaysian lower and higher-
grade timber species. Two types of beams were prepared which were mono-species
and mixed-species glulam. Mono-species glulam with uniform layup were fabricated
using Merpauh, Jelutong and Sesendok. Mixed-species glulam with balanced layup
were fabricated whereby Merpauh was positioned equally at the outer layers and
either Jelutong or Sesendok were positioned at the inner layers. Three replicates of
ten-layered glulam beams measuring 100 mm in width, 300 mm in depth and 6200
mm in length were manufactured according to MS758 for each mono and mixed-
species glulam. Bending, delamination and block shear tests were done on all the
glulam beams. The results show that glulam manufactured from the combination of
Sesendok and Merpauh obtained the highest bending properties and structural
efficiency. In addition, the bonding performance at the interface between
Sesendok-Merpauh lamellas proved to be excellent.
Keywords: Glulam, Mixed-species, Bending properties, Bonding properties,
Delamination, Shear glue line
Abstrak
Kajian ini dijalankan bagi melihat prestasi lenturan dan lekatan bagi rasuk kayu
berperekat yang dihasilkan melalui gabungan kayu tropika Malaysia dari spesis kayu
berkekuatan rendah dan kayu berkekuatan tinggi. Dalam kajian ini, dua jenis rasuk
telah dibangunkan iaitu dari spesis tunggal sebagai sampel kawalan dan juga rasuk
dari spesis campuran. Rasuk dari spesis tunggal dibina secara seragam dengan
menggunakan spesis kayu Merpauh, Jelutong dan Sesendok. Rasuk spesis campuran
pula dibina dengan kedudukan simetri di mana lapisan luar pada bahagian atas
dan bawah rasuk adalah dari spesis kayu Merpauh manakala bahagian lapisan
dalaman adalah dari spesis kayu Jelutong atau Sesendok. Bagi ujikaji makmal, tiga
batang sampel dari setiap rasuk kayu berperekat dari spesis tunggal dan spesis
campuran telah dibina. Sampel rasuk yang dibina ini terdiri daripada sepuluh lapisan
kayu panel yang dilekatkan dengan keratan rentas rasuk berukuran 100 mm lebar
dan 300 mm dalam. Panjang setiap rasuk pula berukuran 6200 mm. Semua rasuk ini
dibina berpandukan standard Malaysia, MS758. Ujikaji lenturan, delaminasi dan blok
ricihan telah dijalankan ke atas semua sampel kajian. Keputusan kajian
menunjukkan rasuk kayu berperekat dari spesis campuran Sesendok dan Merpauh
telah memperolehi sifat lenturan yang tinggi dan mempunyai struktur rasuk yang
lebih kuat berbanding dari sampel rasuk yang lain . Dalam kajian ini juga, prestasi
lekatan bagi antara muka lapisan kayu bagi rasuk spesis campuran Sesendok dan
Merpauh dibuktikan lebih baik.
Kata kunci: lapisan kayu berperekat, spesis kayu campuran, sifat lenturan, sifat
lekatan, delaminasi, ricihan garisan lekatan
© 2019 Penerbit UTM Press. All rights reserved
Glued Laminated
Timber (Glulam)
Mono and mixed-
species using Merpauh,
Jelutong and Sesendok
Bending and Bonding
Properties

166 Wan Hazira, Norshariza & Zakiah / Jurnal Teknologi (Sciences & Engineering) 81:4 (2019) 165–170
1.0 INTRODUCTION
Glue laminated timber is defined in ASTM D3737
Standard Practice Establising Allowable Properties
of Structural Glued Laminated Timber (Glulam) as
“a material glued up from suitably selected and
prepared pieces of wood whether in straight or
curve form with the grain of all pieces essentially
parallel to the longitudinal axis of the member.”
Structural glulam is one of the oldest and
established structural members and is widely used
in developed country yet in Malaysia, the usage is
only gaining acceptance in the construction
industry. Recently, the Malaysia Timber Industry
Board built an iconic glulam building using Resak
and Keruing in Johor and it was recognized as the
first building completed using glulam in Malaysia.
Another recently completed project incorporating
glulam is the Head Quarters of the Crops for the
Future in Semenyih, Selangor.
One of the important characteristics in glulam
manufacturing is that bonding of laminations
produces beams with higher strength as compared
to the strength of solid timber with the same
dimensions [2]. This increase in strength is important
because the quality of lamination is dependent on
its magnitude. Laminating also allows the dispersion
of timber defects throughout the length of the
glulam member by redistributing stress of the
defect through the clear wood of adjacent
laminations [3]. In addition, laminating allows
control over the positioning of different grades of
timber within the glulam member cross-section. By
placing the strongest timbers in the regions of
greater stress e.g. the top and bottom of a
bending member, the performance of the glulam
members can be further enhanced [4].
Nearly any species or mixed-species
combination can be used to manufacture glulam,
provided its physical, mechanical and bonding
properties are suitable and the timbers can be
glued together [2]. Glulam members
predominantly consist of softwood as they are the
main source of structural timber, however
hardwoods are slowly gaining importance in
glulam production [5]. Mixed species combination
commonly used in the United States include
Douglas Fir (Pseudotsuga menziesii)–Larch (Larix
occidetalis), Hemlock (Tsuga heterophylla)–
Douglas Fir and Spruce (Picea spp.)–Pine (Pinus
spp.)–Fir–Red Maple (Acer spp.) [6]. Other mixed
species combination studied by other reserachers
includes Poplar (Populus X euramaricana) -
Eucalyptus (Eucalyptus grandis) [4] as well as Sugi
(Cryptomeria japonica) - Hinoki (Chamaecyparis
obtuse) and Douglas Fir [7].
Although extensive research has been
conducted on glulam [8-11], limited studies have
been conducted to investigate the physical and
mechanical properties of glulam using Malaysian
hardwood timbers. Among the recent studies
conducted include works done by Wan Mohamad
et al. (2011), Wan Hazira et al. (2014) and
Norshariza et al. (2014 and 2016]. Wan Mohamad
et al. (2011) studied the bending strength of Resak
and Keruing glulam and reported that the
maximum bending capacity of both glulam beams
were higher than the allowable bending strength
stated in MS544 Part 3. This indicates that glulam
beam using Malaysian timber is suitable as
structural members. It was also found that glulam
fabricated using lower density timber namely
Merpauh (Strength Group 4) and Bintangor
(Strength Group 5) was able to improve the
strength of the timber through glulam technology
(Wan Hazira et al., 2014). However, for timber with
higher density (such as Strength Group 2 and
Strength Group 3), the bending strength of glulam
was at par with the bending strength of solid timber
for that particular strength grade [14-15].
In Malaysia, heavy and medium hardwoods
(SG1-SG4) are normally used as load bearing
members. However not all of these species are
suitable for glulam manufacturing. These higher
grades, higher density timbers have difficult gluing
characteristics and are expensive. On the other
hand, light hardwoods (SG4-SG7) are mostly used
for non-structural applications and do not
represent efficient use of available timber. One
way of fully utilizing and upgrading these timbers is
by converting them into glulam and by combining
with proven high quality timber species. The main
objective of this study is to determine the effect of
using Malaysian lower-grade species combined
with higher-grade species on the bending and
bonding properties of glulam beams.
2.0 METHODOLOGY
2.1 Materials
The species used to manufacture glulam beams
were Merpauh (Swintonia spp.), Jelutong (Dyera
spp.) and Sesendok (Endospermum spp.). The
strength group and density of each timber species
are shown in Table 1. The species selected is based
on availability and strength groups namely SG4 for
Merpauh, SG6 for Jelutong and SG7 for Sesendok.
Phenol resorcinol formaldehyde (PRF) adhesive
and hardener obtained from Dynea NZ Limited
(Prefere 4001-2 and Prefere 5837) were used during
end jointing and lamination.
Table 1 Strength group and density of timber species
Timber species
Strength Group
(SG) [16]
Density (kg/m3)
[17]
Merpauh
4
640 – 880
Jelutong
6
415 – 495
Sesendok
7
305 - 655
2.2 Specimen Preparation
All timbers used for glulam manufacturing were
graded into Hardwood Structural (HS) grade in
accordance with MS1714. Two types of glulam
beams were prepared; (i) mono-species with
uniform layup and (ii) mixed-species with balanced

166 Wan Hazira, Norshariza & Zakiah / Jurnal Teknologi (Sciences & Engineering) 81:4 (2019) 165–170
layup (Figure 1). Three mono-species glulam were
prepared using only Merpauh, Jelutong and
Sesendok. For the mixed-species glulam, the
positioning of the higher and lower strength grade
timber in a beam was according to
recommendations made in MS544 Part 3. The
higher strength grade timber species i.e. Merpauh
were equally positioned at the outer layers while
the lower grade timber species, namely Jelutong
and Sesendok were positioned at the inner layers
of the beam. The depth of the higher-grade
species was 40% of the total glulam beam depth.
The lower grade species for the inner lamella was 2
to 3 grades lower than the outer lamella, as shown
in Figure 1. The compositions of the mixed-species
glulam were Jelutong-Merpauh and Sesendok-
Merpauh. The glulam beam manufactured had
dimensions of 6200 mm in length by 100 mm in
width and 300 mm in depth, as shown in Figure 2.
Figure 1 Beam composition of glulam
Figure 2 Dimension of glulam
2.3 Test Method
2.3.1 Bending Test
A three-point load bending test was set-up as
shown Figure 3. The test was conducted according
to ASTM D198. The bending strength, SR and
modulus of elasticity, Ef were calculated according
to the following equations. The actual bending test
set-up is shown in Figure 4.
 
 (1)
 
 (2)
where Pmax is the maximum load borne by beam
loaded to failure (N), L is the span of the beam
(mm), b is the width of the beam (mm), h is the
depth of the beam (mm), a is the distance from
reaction to nearest load point (1/3 shear span)
(mm), P is the increment of applied load below
proportional limit (N) and Δ is the increment of
deflectioin of beam’s neutral axis measured at mid
span.
Figure 3 Schematic diagram of bending test set-up
Figure 4 Actual bending test set-up
2.3.2 Delamination Test
Delamination test was conducted in accordance
with MS758. Method A was applied because the
adhesive used in this study to manufacture glulam
beams was Type I Adhesive. The specimens for
delamination test were extracted from the full cross
section of the glulam beam and represented the
glulam production run. The specimens were cut
perpendicular to the grain of the glulam member
and had dimensions of 75 mm in length (along the
grain) by 100 mm in width and 300 mm in depth.
Five replicates were tested for each glulam beams.
The test specimens were subjected to two test
cycles and an extra cycle was carried out for test
specimens having a total delamination
percentage of 5 and above. The lengths of the
open glue lines on end grain surface for each test
specimen were measured at the end of the test.
2.3.3 Block Shear Test
Block shear test on the glue lines were conducted
according to MS758. The test specimens were
taken from the full cross-section of the glulam
beam and 1100 mm away from the edge of the
beam. Specimens were cut perpendicular to the
grain direction. All nine glue lines of each glulam
beam specimens were tested. The dimension of
the test specimens were 50 mm in length by 50 mm
300
mm
300
mm
300
mm
1800
mm
1800
mm
1800
mm
5400
mm

167 Wan Hazira, Norshariza & Zakiah / Jurnal Teknologi (Sciences & Engineering) 81:4 (2019) 165–170
in width and 50 mm in depth, with the glue line at
the center of the specimen. A 1000 kN universal
testing machine was used to test all the specimens.
Constant load was applied and load readings was
continuously detected and recorded up to the
ultimate load, after at least 20 seconds. Shear
strength were calculated and wood failure
percentage were also determined.
3.0 RESULTS AND DISCUSSION
3.1 Bending Properties of Glulam
The bending properties of mono and mixed-
species glulam beams were analyzed in terms of
modulus of rupture (bending strength) and
modulus of elasticity. Three replicates were tested
for each glulam beam and the mean and
coefficient of variation (COV) was calculated.
From Figure 5 and Figure 6, a clear difference
between mixed Sesendok-Merpauh and others
can be seen, both in the case of mono and mixed-
species glulam. Figure 5 shows that the highest
modulus of elasticity, with respect to Merpauh was
obtained using mixed Sesendok-Merpauh
(+35.73%) while mixed Jelutong-Merpauh showed
lower increase (+20.10%).
Figure 5 Modulus of elasticity in static bending
In the case of bending strength, as shown in Figure
6, the maximum increase (+36.50%) with respect to
Merpauh was also found for mixed Sesendok-
Merpauh glulam while mixed Jelutong-Merpauh
showed lower increase (+18.68%).
Out of the two mixed-species glulam, Sesendok-
Merpauh obtained the highest bending properties
whereby the percent increase of bending strength
was 36.50%, 4.86% and 28.83% when compared
against Merpauh, Jelutong and Sesendok,
respectively. In addition, the percent increase of
modulus of elasticity for Sesendok-Merpauh glulam
when compared against Merpauh, Jelutong and
Sesendok were 35.73%, 141.84% and 156.75%
respectively.
Table 2 shows the summary of the mean values
for density, bending strength modulus of elasticity
and structural efficiency for all glulam beams
studied. The COV values are quite low indicating a
low dispersion of mean values for both bending
strength and modulus of elasticity.
Figure 6 Bending strength
Figure 5 Load versus displacement curve
Table 2 Mean values, coefficient of variation and structural effciency of each species of beams for the bending
characteristic
Species
Density
(kg/m3)
Bending strength
(N/mm2)
Structural
efficiency for
Bending strength
Modulus of
elasticity
(N/mm2)
Structural
efficiency for
Modulus of
elasticity
Merpauh
8.69 (0.66)
31.75 (7.15)c
0.04
17800 (0.56)c
20.48
Mixed Jelutong-
Merpauh
626 (1.88)
37.68 (2.44)ab
0.06
21370 (8.56)b
34.14
Mixed Sesendok-
Merpauh
613 (1.15)
43.34 (13.73)a
0.07
24160 (8.49)a
39.41
Jelutong
492 (2.39)
41.33 (1.4)a
0.08
9990 (12.61)d
20.30
Sesendok
487 (1.93)
33.64 (6.78)bc
0.07
9410 (2.55)d
19.32
Note: COV in parentheses. Same letters are not significant at 0.05 according to Duncan’s Multiple Range Test.
0
5000
10000
15000
20000
25000
Modulus of Elasticity (N/mm2)
0
10
20
30
40
50
Bending strength (N/mm2)

168 Wan Hazira, Norshariza & Zakiah / Jurnal Teknologi (Sciences & Engineering) 81:4 (2019) 165–170
The load displacement curve under bending for all
the beam studied is presented in Figure 7.
Generally, all the beams had linear elastic
behavior until failure occurred. The curve pattern
indicated brittle behavior because all the beams
failed abruptly after reaching ultimate load.
Mixed-species glulam obtained higher ultimate
load compared to mono-species glulam, which
indicates that mixed-species glulam beams are
able to sustain bigger load when subjected to
bending.
Figure 7 Load versus displacement curve
3.2 Delamination in the Glue Line
Figure 8 shows the average total delamination
percentages after two cycles for all the glulam
beams studied. The data indicates excellent quality
of the glue lines in both mono and mixed species
glulam beams. Eventhough Merpauh showed
mixed results whereby one replicate exceeded the
allowable maximum value set forth in MS758, the
mean value of the average total delamination
percentage for Merpauh was 4.3% which is below
the maximum requirement value of 5%. Low
delamination percentage in the glue lines between
Merpauh and Jelutong as well as Merpauh and
Sesendok indicated non-existance of gluing
problems at the interface between these wood
species. This could be due to the similarity in
shrinkage values for the species studied, as shown
in Table 3.
Figure 8 Average total delamination after two initial
cycles in percentage
Table 3 Shrinkage percentages of Merpauh, Jelutong and
Sesendok
Species
Shrinkage percentage (%)
Radial
Tangential
Merpauh
(S. Schwenkii)
1.4
2
Jelutong
(Dyera spp.)
0.8
2
Sesendok
(Endospermum spp.)
1.2
1.3
Note: Data obtained from a dictionary of Malaysian Timbers [12].
3.3 Shear Strength of Glue Line
The average glue line shear strength and relative
wood failure of all the glulam beams studied are
summarized in Table 4. Generally, all the glulam
beams fulfill the MS758 requirement which set forth
a minimum of 6.0 N/mm2 shear strength, while for
lighter density timber, a shear strength of 4.0 N/mm2
is acceptable provided the wood failure
percentage is 100%. For wood failure that did not
reach 100%, the values obtained were compared
against the acceptance criteria stated in MS758.
For shear strength of 11 N/mm2, the minimum wood
failure must be above 45% thus Merpauh, mixed
Jelutong-Merpauh and mixed Sesendok-Merpauh
met the requirement.
For shear strength of 8 N/mm2, the minimum
wood failure must be above 72% so both Jelutong
and Sesendok met the requirement. This indicates
good load carrying capability of the glue line in all
the glulam studied as well as confirms the reliability
of bonding found in the delamination tests.
0
10
20
30
40
50
60
70
80
020 40 60 80 100 120
Load (kN)
Displacement (mm)
Merpauh Mixed Jelutong-Merpauh
Mixed Sesendok-Merpauh Jelutong
Sesendok
0
1
2
3
4
5
6
7
8
9
Average total delamination (%)
Replicate 1 Replicate 2 Replicate 3
MS758<5%

169 Wan Hazira, Norshariza & Zakiah / Jurnal Teknologi (Sciences & Engineering) 81:4 (2019) 165–170
Table 4 Shear strength and relative wood failure
Species
Shear
Strength
Wood
Failure
Criteria
(N/mm2)
(%)
Merpauh
16.56
(12.51)
80.86
Met
Mixed
Jelutong-
Merpauh
10.36
(35.06)
77.13
Met
Mixed
Sesendok-
Merpauh
14.29
(22.39)
88.68
Met
Jelutong
8.07 (7.33)
85.81
Met
Sesendok
9.56 (15.27)
77.13
Met
Note: COV in parentheses.
4.0 CONCLUSION
For all the glulam beams studied, mixed species
beams showed higher bending properties as well
as structural efficiency than those constructed
entirely from Merpauh, Jelutong or Sesendok. The
best bending performance between mixed species
glulam is the combination of Sesendok and
Merpauh. In addition, the excellent quality of the
glue lines between laminates also contributed to
the performance of the glulam beams. The results
obtained from this study confirm the possibility of
producing high structural efficiency glulam beams
by combining two different timber species.
Acknowledgement
Malaysia Timber Industry Board (MTIB) financially
supported the work reported here. We wish to
thank the technicians of Civil Engineering Faculty,
Universiti Teknologi MARA (UiTM) and Loji
Pengeringan Tanor MTIB, Konsortium PEKA Sdn Bhd
for their assistance and support.
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