- Email: [email protected]
Effects of scarf joints on bending strength and modulus of elasticity to laminated veneer lumber (LVL)
ARTICLE IN PRESS
Building and Environment 42 (2007) 1510–1514 www.elsevier.com/locate/buildenv
Effects of scarf joints on bending strength and modulus of elasticity to laminated veneer lumber (LVL) Ayhan O¨zc- ifc- i Technical Education Faculty, Zonguldak Karaelmas University, 78 050 Karabu¨k, Turkey Received 10 November 2005; received in revised form 6 December 2005; accepted 15 December 2005
Abstract The role of geometry on the mechanical performance of scarf joints in laminated veneer lumber (LVL) bonded with phenol formaldehyde and melamine formaldehyde (MF) adhesives was investigated. Model joints consists of 3, 4 and 5 mm veneer thicknesses at 301, 451 and 601 of varying scarf joints for LVL produced from brutia pine (Pinus brutia Ten) and elm (Ulmus compestris l.) woods. However, there is little information available concerning the bending strength and modulus of elasticity for LVL, and in particular, scarf joints in these field. In this study, it was aimed to determine the bending strength and modulus of elasticity for LVL. For this purpose, samples were tested according to TS EN 310 standard. It was observed that the highest bending strength (291.5 N/mm2) and modulus of elasticity (28 101 N/mm2) were obtained in control (solid wood) samples having three layered LVL, jointed with 301 angle and bonded with MF adhesive. As a result of the effects scarf joints on bending strength and modulus elasticity test, if the scarf angle decreases, the properties of LVL increase. r 2006 Elsevier Ltd. All rights reserved. Keywords: Bending strength; Scarf joint; LVL; Phenol; Melamine formaldehyde
1. Introduction Laminated veneer lumber (LVL) is an engineered wood product manufactured from veneers that are rotary peeled, dried and laminated together with parallel oriented grains under heat and pressure with a waterproof adhesive. A higher strength product can be produced by this method from low-grade logs, due to the dispersion of defects from veneer to veneer, than could be realized by sawing the some low-grade log [1,2]. One of the most significant technical advantages of LVL is that specific performance characteristic can be incorporated in to its design. By the nature of their manufacturing process, large defects such as knot and other strength-reducing characteristics are either eliminated or dispersed throughout the cross-section to produce a more homogeneous product [3,4]. Because of the uniformity in properties, high strength and availability in virtually unlimited length and size, in a variety of products, such as commodity structural components, floor beams, garage door, window and door headers, valley rafters, scaffold planking, and the flange 0360-1323/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2005.12.024
material for particleboard wood I-joints and ridge and hip beams [2]. Before the development of engineering wood products, builders were limited to large solid sawn timber which often does not have the dimensional stability and uniformity required. The LVL manufacturing process creates a strong and stable product that can reliably support large areas. A second important benefit of LVL is that the veneering and gluing process enables large beams to be made from relatively small diameters logs of many species, thereby providing for efficient use of forest resources [2]. Due to their advantages mentioned above, LVL has been suggested as a good alternative for structural purposes [9]. However, the results of researches about exposure durability of this material are contradictory to each other [5,6]. LVL produced from solid wood material is of more benefit, and is used as a building element and furniture material. It is possible to produce LVL in the desired quality and from with lamination techniques, so long distances can be passed thoroughly. The quality of material is improved by removing natural defects of wood used in the production of LVL.
ARTICLE IN PRESS A. O¨zc- ifc- i / Building and Environment 42 (2007) 1510–1514
Toksoy et al. [6] stated that the highest bending strength (103.8 N/mm2) and modulus of elasticity (79.59 N/mm2) for LVL bonded with 12 percent MF content were obtained in beech samples. Efficient usage of LVL in the construction industry requires an understanding of structural behavior of numerous species and knowledge about to the effects of log pre-treatment process on the mechanical properties and durability of LVL [2]. In case of the wood material using for building element has short dimensions, different butt joint types which are scarf joint, finger joint, lap joint, tongue and groove joint etc., can be applied. Therefore, the aim of this study was to determine the effects of scarf joints on the bending strength and modulus of elasticity of LVL produced from elm wood and brutia pine bonded with MF and PF adhesives, and also the effects on the three, four and five-layered construction with scarf joints at 301, 451 and 601 degree angles. 2. Materials and method Woods: elm wood and brutia pine, widely used in the woodworking industry, were chosen at random from timber merchants in Ankara, Turkey. Adhesives: the TS 3891 [7] and BS EN 204 [8] standards procedure were followed for applying PF and MF adhesive. The density of PF should be 1.15–1.18 g/cm3, the viscosity 13.00072.000 m Pa s, and pH value is 7.5–8.5, the solidify time is 2–4 min, respectively. It is recommended that PF should be applied to one surface at the ratio of 180 g/m2, and should be held for about 2–4 min. After the hot-pressing process, the materials should be held until it backs to normal temperature. PF and MF were supplied from producer firm Polisan Izmit, Turkey. MF can be applied in the hot temperature. Its density is 1.22–1.24 g/cm3, pH is about 9.3–9.6, and viscosity is 12.00073.000 m Pa, respectively. The solidify time is–2-3 min. It is recommended that MF should be applied to one surface at the ratio of 180 g/m2, and should be held for about 2–4 min. After the hot-pressing process, the materials should be held until it reduces to normal temperature.
1511
2.1. Preparation of Experimental Samples The samples cut from sapwood were conditioned at 2072 1C and 65%73% relative humidity until their weights became stable by storing them for three months in the conditioning room. Test samples having 12% average moisture content were cut with the dimension of 4, 5 and 6.7 mm thickness by 20 mm width and 360 mm length, and also each of LVL was made in 3, 4 and 5 layered. In order to obtain 20 mm thickness, 5 layers with each of 4 mm veneer thickness (4 5 ¼ 20 mm) or 3 layers with each of 6.7 mm veneer thickness (6.7 3 ¼ 20.1 mm) were bonded with PF and MF applied to one surface of the veneer at the ratio of 180 g/m2. To prepare test samples, firstly, LVL was sawn in slant and jointed with adhesives. Finally, scarf joint test samples were prepared. Scarf joint is an end joint formed by joining with adhesive the ends of two pieces that have been tapered or beveled to form sloping plane surfaces. Prepared test samples are shown in Fig. 1. 2.2. Test method Bending-strength experiments were performed according to the principles of the TS 2474 [10] standard by using a 4000-kp capacity universal test machine, and applying 6 mm/min loading time, as shown in Fig. 2. The loading was continued until breaking occurs on the surface of the test samples; meanwhile, observing load (Fmax), bending strength of sample (A, N/mm2) and bending strength (sb) were calculated by using 3F max ðN=mm2 Þ, (1) 2bh2 where; sb is the bending strength (N/mm2), Fmax the maximum load (N), L the distance between two supports (300 mm), h is the specimen thickness (20 mm), b the width of sample (20 mm). The modulus of elasticity was also measured by a universal testing machine according to the procedure in the sb ¼
Fig. 1. Test samples [9].
ARTICLE IN PRESS A. O¨zc- ifc- i / Building and Environment 42 (2007) 1510–1514
1512
Table 1 Air-dry densities values obtained from test samples Species of wood
Type of adhesive Number of layer Air-dry density (g/cm3)
Elm wood
Control Melamine Formaldehyde
Fig. 2. The stand of the bending strength test. Phenol Formaldehyde
TS EN 310 [11]. For this test, untreated LVL (20 20 360 mm) and impregnated LVL samples were used. There were ten replications for control and treatment. Modulus of elasticity (sE) was calculated from sE ¼ 0:25 ðP2
P1 ÞL3s =Dp b h3 ,
Brutia pine
Control Melamine Formaldehyde Phenol Formaldehyde
(2)
where P2 is the second force (kg), P1 is the first force, Ls3 the distance between supports (cm), Dp the difference of buckling, b the width of sample(cm), h the thickness of sample (cm). 3. Data analyses By using two different species of wood materials, three different types of layer thicknesses, four different kind angles (control, 301, 451 and 601) and two different types of adhesives as parameter, for both test methods, a total of 480 samples (2 3 4 2 10) were prepared having ten samples for each parameter. Firstly, multiple variance analyses were used for determining the differences between the groups, Secondly, the Duncan test was used to determine whether the differences have any significant level.
— 3 4 5 3 4 5 — 3 4 5 3 4 5
0.63 0.74 0.77 0.81 0.70 0.75 0.79 0.50 0.54 0.56 0.60 0.50 0.54 0.59
Table 2 Average values of bending strength Sources
Type of factor
Average values (N/mm2)
Wood material
Elm Brutia MF PF Control 301 451 601 3 4 5
170.8 116.4 190.7 141.4 178.6 150.0 106.4 086.5 168.0 136.6 119.0
Type of adhesive Type of construction
Number of layer
4. Result and discussion The average values of air densities obtained from the test samples are given in Table 1. According to the control samples, there are linear increases in density of the LVL samples, when the number of layers increases, the density of LVL increases automatically, depending on the type of adhesive. The average values of the bending strength and modulus of elasticity obtained from different species of wood materials are given in Table 2. Three-layered LVL is found more eminent than four and five-layered, because three-layered LVL has more solid wood material than the others. According to the average values of bending strength and interactions in regard to the effects of factor types, the highest bending strength has been determined in three-layered elm wood lamination bonded with MF adhesive. In other words, the highest bending strength was obtained from the elm wood as 170.8 N/mm2, in MF adhesive as 190.7 N/mm2, in 301 as 150.0 N/mm2, and in three-layered lamination as 168.0 N/ mm2, respectively, and the results of the multiple variance analyses connected with these values (Pp0.05).
The difference between the groups regarding the effect of variance sources on bending strength and modulus of elasticity is meaningful regarding to 5% of probability. Duncan test results conducted to determine the importance of the differences between the groups are given in Table 3, and also, a schematic illustration can be seen in Fig. 3. It shows that the highest bending strength was determined in elm wood bonded with MF having three-layered lamination, the lowest value was observed in pine bonded with PF having five layered and jointed end to end at 601. As for the modulus of elasticity of LVL, the highest value was obtained in brutia pine LVL with MF adhesive. A schematic illustration can be seen in Fig. 4. 5. Conclusion To obtain acceptable strength in pieces spliced together endwise, it is necessary to make a scarf joint, finger or other sloped joints. As the joint angle decreases from 601 to 301 or lower, the bending strength increases. The plain scarf with a low slope generally develops the highest strength,
ARTICLE IN PRESS A. O¨zc- ifc- i / Building and Environment 42 (2007) 1510–1514
1513
Table 3 Average values of test categories (N/mm2) Species of wood
Type of construction
Type of adhesive
Number of layer
Bending strength
HG
Modulus of elasticity
HG
Elm wood
Control
MF
3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5
291.5 186.3 178.0 178.7 168.3 179.5 223.4 144.3 144.2 117.8 151.8 141.8 112.8 111.3 109.8 196.4 162.8 151.9 113.1 119.9 96.1 85.9 64.6 50.1 172.9 170.1 151.1 191.3 121.3 110.1 158.9 131.2 120.0 141.8 131.6 121.4 130.0 125.7 98.1 111.0 109.0 100.1 111.8 112.0 110.0 90.0 87.0 60.0 11.6 5.63
a cd d d c–e c b fg fg h ef fg h h h–k dc de ef h g–k h–k h–k n n c c f–g c gh h ef h h g gh gh gh gh h h h–k h–k h h h h–k k–m n
25212 23674 22700 22718 21224 20118 24308 18126 18126 14789 19107 17674 14296 13176 12338 24010 21210 19108 14218 14916 11716 11680 11120 11100 28101 28012 27118 19213 14763 14100 19316 16318 15129 18316 16401 15016 17204 15816 12618 16610 16403 17606 16403 15126 15590 15180 15003 15030 4872 10.12
c d e e de e b g g k f h k l l c de f k j m m mn mn a a b f kl l f hi j g fh gh h gh k hi hi h h–i j j j j j
PF
301
MF
PF
451
MF
PF
601
MF
PF
Brutia pine
Control
MF
PF
301
MF
PF
451
MF
PF
601
MF
PF
LSD value Coefficient of variance HG: Group of homogeneity.
but it is most wasteful material and requires considerable care in both machining and gluing to obtain consistently high-quality joints. If the grain of a board makes an angle with the board’s face, the scarf should be cut with the slope of the grain rather than against to. According to the control samples, there are linear increases in density of the LVL samples, when the number of layers increases, the density of LVL increases auto-
matically, depending on the type of adhesive. The highest density was obtained in LVL samples bonded with MF adhesive, so it can be said that the adhesive increased the density. In literature, Toksoy et al. [6] stated that the adhesive used for LVL was affected the air dry density as 0.68 and 0.49 g/cm3, respectively. Among the test samples, control (solid wood) samples gave the highest bending strength and it was also observed
ARTICLE IN PRESS A. O¨zc- ifc- i / Building and Environment 42 (2007) 1510–1514
Bending strength (N/mm2)
1514 350 300
Control
30°
45°
60°
250 200 150 100 50 0 E-MF-3 E-MF-4 E-MF-5 E-PF-3 E-PF-4 E-PF-5 B-MF-3 B-MF-4 B-MF-5 B-PF-3 B-PF-4 B-PF-5
Types of construction, adhesives and layer
Fig. 3. The effects of scarf joint types on the bending strength of control and LVL samples.
Modulus of elasticity (N/mm2)
30800
Control
30°
45°
60°
25800 20800 15800 10800 5800 E-MF-3 E-MF-4 E-MF-5 E-PF-3 E-PF-4 E-PF-5 B-MF-3 B-MF-4 B-MF-5 B-PF-3 B-PF-4 B-PF-5
Types of construction, adhesives and layer
Fig. 4. The effects of scarf joint types on the modulus of elasticity.
that, when the joint angle increases from 30 to 601, the bending strength decreases. 301 joint angle gave the highest bonding strength. Because, the bonding area more than the others. And also, MF adhesive gave a high quality bonding surface [6]. Increasing the number of layers in LVL did not affect on the bending strength. Since five layered samples gave the lowest value. Bostro¨m [12] explained that timber beams has a small depth, it gives less than 10 000 MPa for a modulus of elasticity in accordance with European Standard EN 408. This result is less than the outcomes shown in Table 1. However, the test method in both studies is different despite having used the similar application procedure. As a result, it is advised that the serviceability of LVL production depends on, firstly, the kind of wood and its preparation for use, secondly, the type and quality of the adhesive, thirdly, the compatibility of the gluing process with the wood and adhesive used, and lastly, the type of joint and assembly. References [1] Llaufenberg T. Exposure effects upon performance of laminated veneer lumber and glulam materials. Forest Product Journal 1982;32(5):42–8. [2] Semra C - , Gursel C - , Ismail A. Effects of log steaming, veneer drying and aging on the mechanical properties of laminated veneer lumber (LVL). Building and Environment, in press.
[3] Wang X, Ross RJ, Brashaw BK, Verhey SA, Formsan JW, Ericson JR. Flexural Properties of laminated veneer lumber manufactured from ultrasonically rated red maple veneer. Forest Product Laboratory, FPL-RN-0288, 2003. [4] Hing PS, Paridah MT, Zakiah A. Edgewise bending properties of LVL: effects of veneer thickness and species. In: The proceeding of USM-JIRCAS joint international symposium, lignocellulosesmaterial of the millennium. 3–5 April. 2005. Washington State University, Washington, USA, p. 3–14. [5] Kamala BS, Kumar P, Rao RV, Sharma SN. Performance test of laminated veneer lumber (LVL) from rubber wood for different physical and mechanical properties. Holz als Roh-und Werkstoff 1999;57(2):114–6. [6] Toksoy D, Gursel C - , Ismail A, Semra C - , Cenk D. Technological and economic comparison of the usage of beech and alder wood in plywood and laminated veneer lumber manufacturing. Building and Environment, in press. [7] TS 3891. Adhesives-polyvinyl acetate emulsions. Institute of Turkish Standards, 1983. [8] BS EN 204 Non-structural adhesives for joining of wood and derived timber product. British Standards, 1991. [9] TS EN 386. Properties of bonded lamination wood performance and conditions of minimum manufacturing. Institute of Turkish Standards, 1999. [10] TS 2474. Determination of static bending properties of wood. Institute of Turkish Standards, 1976. [11] TS EN 310. Wood based panels—The determination of static bending strength and modulus of elasticity. Institute of Turkish Standards, 1999. [12] Bostro¨m L. Determination of the modulus of elasticity in bending of structural timber-comparison of two methods. Holz als Roh-und Werkstoff 1999;57:145–9.
Building and Environment 42 (2007) 1510–1514 www.elsevier.com/locate/buildenv
Effects of scarf joints on bending strength and modulus of elasticity to laminated veneer lumber (LVL) Ayhan O¨zc- ifc- i Technical Education Faculty, Zonguldak Karaelmas University, 78 050 Karabu¨k, Turkey Received 10 November 2005; received in revised form 6 December 2005; accepted 15 December 2005
Abstract The role of geometry on the mechanical performance of scarf joints in laminated veneer lumber (LVL) bonded with phenol formaldehyde and melamine formaldehyde (MF) adhesives was investigated. Model joints consists of 3, 4 and 5 mm veneer thicknesses at 301, 451 and 601 of varying scarf joints for LVL produced from brutia pine (Pinus brutia Ten) and elm (Ulmus compestris l.) woods. However, there is little information available concerning the bending strength and modulus of elasticity for LVL, and in particular, scarf joints in these field. In this study, it was aimed to determine the bending strength and modulus of elasticity for LVL. For this purpose, samples were tested according to TS EN 310 standard. It was observed that the highest bending strength (291.5 N/mm2) and modulus of elasticity (28 101 N/mm2) were obtained in control (solid wood) samples having three layered LVL, jointed with 301 angle and bonded with MF adhesive. As a result of the effects scarf joints on bending strength and modulus elasticity test, if the scarf angle decreases, the properties of LVL increase. r 2006 Elsevier Ltd. All rights reserved. Keywords: Bending strength; Scarf joint; LVL; Phenol; Melamine formaldehyde
1. Introduction Laminated veneer lumber (LVL) is an engineered wood product manufactured from veneers that are rotary peeled, dried and laminated together with parallel oriented grains under heat and pressure with a waterproof adhesive. A higher strength product can be produced by this method from low-grade logs, due to the dispersion of defects from veneer to veneer, than could be realized by sawing the some low-grade log [1,2]. One of the most significant technical advantages of LVL is that specific performance characteristic can be incorporated in to its design. By the nature of their manufacturing process, large defects such as knot and other strength-reducing characteristics are either eliminated or dispersed throughout the cross-section to produce a more homogeneous product [3,4]. Because of the uniformity in properties, high strength and availability in virtually unlimited length and size, in a variety of products, such as commodity structural components, floor beams, garage door, window and door headers, valley rafters, scaffold planking, and the flange 0360-1323/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2005.12.024
material for particleboard wood I-joints and ridge and hip beams [2]. Before the development of engineering wood products, builders were limited to large solid sawn timber which often does not have the dimensional stability and uniformity required. The LVL manufacturing process creates a strong and stable product that can reliably support large areas. A second important benefit of LVL is that the veneering and gluing process enables large beams to be made from relatively small diameters logs of many species, thereby providing for efficient use of forest resources [2]. Due to their advantages mentioned above, LVL has been suggested as a good alternative for structural purposes [9]. However, the results of researches about exposure durability of this material are contradictory to each other [5,6]. LVL produced from solid wood material is of more benefit, and is used as a building element and furniture material. It is possible to produce LVL in the desired quality and from with lamination techniques, so long distances can be passed thoroughly. The quality of material is improved by removing natural defects of wood used in the production of LVL.
ARTICLE IN PRESS A. O¨zc- ifc- i / Building and Environment 42 (2007) 1510–1514
Toksoy et al. [6] stated that the highest bending strength (103.8 N/mm2) and modulus of elasticity (79.59 N/mm2) for LVL bonded with 12 percent MF content were obtained in beech samples. Efficient usage of LVL in the construction industry requires an understanding of structural behavior of numerous species and knowledge about to the effects of log pre-treatment process on the mechanical properties and durability of LVL [2]. In case of the wood material using for building element has short dimensions, different butt joint types which are scarf joint, finger joint, lap joint, tongue and groove joint etc., can be applied. Therefore, the aim of this study was to determine the effects of scarf joints on the bending strength and modulus of elasticity of LVL produced from elm wood and brutia pine bonded with MF and PF adhesives, and also the effects on the three, four and five-layered construction with scarf joints at 301, 451 and 601 degree angles. 2. Materials and method Woods: elm wood and brutia pine, widely used in the woodworking industry, were chosen at random from timber merchants in Ankara, Turkey. Adhesives: the TS 3891 [7] and BS EN 204 [8] standards procedure were followed for applying PF and MF adhesive. The density of PF should be 1.15–1.18 g/cm3, the viscosity 13.00072.000 m Pa s, and pH value is 7.5–8.5, the solidify time is 2–4 min, respectively. It is recommended that PF should be applied to one surface at the ratio of 180 g/m2, and should be held for about 2–4 min. After the hot-pressing process, the materials should be held until it backs to normal temperature. PF and MF were supplied from producer firm Polisan Izmit, Turkey. MF can be applied in the hot temperature. Its density is 1.22–1.24 g/cm3, pH is about 9.3–9.6, and viscosity is 12.00073.000 m Pa, respectively. The solidify time is–2-3 min. It is recommended that MF should be applied to one surface at the ratio of 180 g/m2, and should be held for about 2–4 min. After the hot-pressing process, the materials should be held until it reduces to normal temperature.
1511
2.1. Preparation of Experimental Samples The samples cut from sapwood were conditioned at 2072 1C and 65%73% relative humidity until their weights became stable by storing them for three months in the conditioning room. Test samples having 12% average moisture content were cut with the dimension of 4, 5 and 6.7 mm thickness by 20 mm width and 360 mm length, and also each of LVL was made in 3, 4 and 5 layered. In order to obtain 20 mm thickness, 5 layers with each of 4 mm veneer thickness (4 5 ¼ 20 mm) or 3 layers with each of 6.7 mm veneer thickness (6.7 3 ¼ 20.1 mm) were bonded with PF and MF applied to one surface of the veneer at the ratio of 180 g/m2. To prepare test samples, firstly, LVL was sawn in slant and jointed with adhesives. Finally, scarf joint test samples were prepared. Scarf joint is an end joint formed by joining with adhesive the ends of two pieces that have been tapered or beveled to form sloping plane surfaces. Prepared test samples are shown in Fig. 1. 2.2. Test method Bending-strength experiments were performed according to the principles of the TS 2474 [10] standard by using a 4000-kp capacity universal test machine, and applying 6 mm/min loading time, as shown in Fig. 2. The loading was continued until breaking occurs on the surface of the test samples; meanwhile, observing load (Fmax), bending strength of sample (A, N/mm2) and bending strength (sb) were calculated by using 3F max ðN=mm2 Þ, (1) 2bh2 where; sb is the bending strength (N/mm2), Fmax the maximum load (N), L the distance between two supports (300 mm), h is the specimen thickness (20 mm), b the width of sample (20 mm). The modulus of elasticity was also measured by a universal testing machine according to the procedure in the sb ¼
Fig. 1. Test samples [9].
ARTICLE IN PRESS A. O¨zc- ifc- i / Building and Environment 42 (2007) 1510–1514
1512
Table 1 Air-dry densities values obtained from test samples Species of wood
Type of adhesive Number of layer Air-dry density (g/cm3)
Elm wood
Control Melamine Formaldehyde
Fig. 2. The stand of the bending strength test. Phenol Formaldehyde
TS EN 310 [11]. For this test, untreated LVL (20 20 360 mm) and impregnated LVL samples were used. There were ten replications for control and treatment. Modulus of elasticity (sE) was calculated from sE ¼ 0:25 ðP2
P1 ÞL3s =Dp b h3 ,
Brutia pine
Control Melamine Formaldehyde Phenol Formaldehyde
(2)
where P2 is the second force (kg), P1 is the first force, Ls3 the distance between supports (cm), Dp the difference of buckling, b the width of sample(cm), h the thickness of sample (cm). 3. Data analyses By using two different species of wood materials, three different types of layer thicknesses, four different kind angles (control, 301, 451 and 601) and two different types of adhesives as parameter, for both test methods, a total of 480 samples (2 3 4 2 10) were prepared having ten samples for each parameter. Firstly, multiple variance analyses were used for determining the differences between the groups, Secondly, the Duncan test was used to determine whether the differences have any significant level.
— 3 4 5 3 4 5 — 3 4 5 3 4 5
0.63 0.74 0.77 0.81 0.70 0.75 0.79 0.50 0.54 0.56 0.60 0.50 0.54 0.59
Table 2 Average values of bending strength Sources
Type of factor
Average values (N/mm2)
Wood material
Elm Brutia MF PF Control 301 451 601 3 4 5
170.8 116.4 190.7 141.4 178.6 150.0 106.4 086.5 168.0 136.6 119.0
Type of adhesive Type of construction
Number of layer
4. Result and discussion The average values of air densities obtained from the test samples are given in Table 1. According to the control samples, there are linear increases in density of the LVL samples, when the number of layers increases, the density of LVL increases automatically, depending on the type of adhesive. The average values of the bending strength and modulus of elasticity obtained from different species of wood materials are given in Table 2. Three-layered LVL is found more eminent than four and five-layered, because three-layered LVL has more solid wood material than the others. According to the average values of bending strength and interactions in regard to the effects of factor types, the highest bending strength has been determined in three-layered elm wood lamination bonded with MF adhesive. In other words, the highest bending strength was obtained from the elm wood as 170.8 N/mm2, in MF adhesive as 190.7 N/mm2, in 301 as 150.0 N/mm2, and in three-layered lamination as 168.0 N/ mm2, respectively, and the results of the multiple variance analyses connected with these values (Pp0.05).
The difference between the groups regarding the effect of variance sources on bending strength and modulus of elasticity is meaningful regarding to 5% of probability. Duncan test results conducted to determine the importance of the differences between the groups are given in Table 3, and also, a schematic illustration can be seen in Fig. 3. It shows that the highest bending strength was determined in elm wood bonded with MF having three-layered lamination, the lowest value was observed in pine bonded with PF having five layered and jointed end to end at 601. As for the modulus of elasticity of LVL, the highest value was obtained in brutia pine LVL with MF adhesive. A schematic illustration can be seen in Fig. 4. 5. Conclusion To obtain acceptable strength in pieces spliced together endwise, it is necessary to make a scarf joint, finger or other sloped joints. As the joint angle decreases from 601 to 301 or lower, the bending strength increases. The plain scarf with a low slope generally develops the highest strength,
ARTICLE IN PRESS A. O¨zc- ifc- i / Building and Environment 42 (2007) 1510–1514
1513
Table 3 Average values of test categories (N/mm2) Species of wood
Type of construction
Type of adhesive
Number of layer
Bending strength
HG
Modulus of elasticity
HG
Elm wood
Control
MF
3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 3 4 5
291.5 186.3 178.0 178.7 168.3 179.5 223.4 144.3 144.2 117.8 151.8 141.8 112.8 111.3 109.8 196.4 162.8 151.9 113.1 119.9 96.1 85.9 64.6 50.1 172.9 170.1 151.1 191.3 121.3 110.1 158.9 131.2 120.0 141.8 131.6 121.4 130.0 125.7 98.1 111.0 109.0 100.1 111.8 112.0 110.0 90.0 87.0 60.0 11.6 5.63
a cd d d c–e c b fg fg h ef fg h h h–k dc de ef h g–k h–k h–k n n c c f–g c gh h ef h h g gh gh gh gh h h h–k h–k h h h h–k k–m n
25212 23674 22700 22718 21224 20118 24308 18126 18126 14789 19107 17674 14296 13176 12338 24010 21210 19108 14218 14916 11716 11680 11120 11100 28101 28012 27118 19213 14763 14100 19316 16318 15129 18316 16401 15016 17204 15816 12618 16610 16403 17606 16403 15126 15590 15180 15003 15030 4872 10.12
c d e e de e b g g k f h k l l c de f k j m m mn mn a a b f kl l f hi j g fh gh h gh k hi hi h h–i j j j j j
PF
301
MF
PF
451
MF
PF
601
MF
PF
Brutia pine
Control
MF
PF
301
MF
PF
451
MF
PF
601
MF
PF
LSD value Coefficient of variance HG: Group of homogeneity.
but it is most wasteful material and requires considerable care in both machining and gluing to obtain consistently high-quality joints. If the grain of a board makes an angle with the board’s face, the scarf should be cut with the slope of the grain rather than against to. According to the control samples, there are linear increases in density of the LVL samples, when the number of layers increases, the density of LVL increases auto-
matically, depending on the type of adhesive. The highest density was obtained in LVL samples bonded with MF adhesive, so it can be said that the adhesive increased the density. In literature, Toksoy et al. [6] stated that the adhesive used for LVL was affected the air dry density as 0.68 and 0.49 g/cm3, respectively. Among the test samples, control (solid wood) samples gave the highest bending strength and it was also observed
ARTICLE IN PRESS A. O¨zc- ifc- i / Building and Environment 42 (2007) 1510–1514
Bending strength (N/mm2)
1514 350 300
Control
30°
45°
60°
250 200 150 100 50 0 E-MF-3 E-MF-4 E-MF-5 E-PF-3 E-PF-4 E-PF-5 B-MF-3 B-MF-4 B-MF-5 B-PF-3 B-PF-4 B-PF-5
Types of construction, adhesives and layer
Fig. 3. The effects of scarf joint types on the bending strength of control and LVL samples.
Modulus of elasticity (N/mm2)
30800
Control
30°
45°
60°
25800 20800 15800 10800 5800 E-MF-3 E-MF-4 E-MF-5 E-PF-3 E-PF-4 E-PF-5 B-MF-3 B-MF-4 B-MF-5 B-PF-3 B-PF-4 B-PF-5
Types of construction, adhesives and layer
Fig. 4. The effects of scarf joint types on the modulus of elasticity.
that, when the joint angle increases from 30 to 601, the bending strength decreases. 301 joint angle gave the highest bonding strength. Because, the bonding area more than the others. And also, MF adhesive gave a high quality bonding surface [6]. Increasing the number of layers in LVL did not affect on the bending strength. Since five layered samples gave the lowest value. Bostro¨m [12] explained that timber beams has a small depth, it gives less than 10 000 MPa for a modulus of elasticity in accordance with European Standard EN 408. This result is less than the outcomes shown in Table 1. However, the test method in both studies is different despite having used the similar application procedure. As a result, it is advised that the serviceability of LVL production depends on, firstly, the kind of wood and its preparation for use, secondly, the type and quality of the adhesive, thirdly, the compatibility of the gluing process with the wood and adhesive used, and lastly, the type of joint and assembly. References [1] Llaufenberg T. Exposure effects upon performance of laminated veneer lumber and glulam materials. Forest Product Journal 1982;32(5):42–8. [2] Semra C - , Gursel C - , Ismail A. Effects of log steaming, veneer drying and aging on the mechanical properties of laminated veneer lumber (LVL). Building and Environment, in press.
[3] Wang X, Ross RJ, Brashaw BK, Verhey SA, Formsan JW, Ericson JR. Flexural Properties of laminated veneer lumber manufactured from ultrasonically rated red maple veneer. Forest Product Laboratory, FPL-RN-0288, 2003. [4] Hing PS, Paridah MT, Zakiah A. Edgewise bending properties of LVL: effects of veneer thickness and species. In: The proceeding of USM-JIRCAS joint international symposium, lignocellulosesmaterial of the millennium. 3–5 April. 2005. Washington State University, Washington, USA, p. 3–14. [5] Kamala BS, Kumar P, Rao RV, Sharma SN. Performance test of laminated veneer lumber (LVL) from rubber wood for different physical and mechanical properties. Holz als Roh-und Werkstoff 1999;57(2):114–6. [6] Toksoy D, Gursel C - , Ismail A, Semra C - , Cenk D. Technological and economic comparison of the usage of beech and alder wood in plywood and laminated veneer lumber manufacturing. Building and Environment, in press. [7] TS 3891. Adhesives-polyvinyl acetate emulsions. Institute of Turkish Standards, 1983. [8] BS EN 204 Non-structural adhesives for joining of wood and derived timber product. British Standards, 1991. [9] TS EN 386. Properties of bonded lamination wood performance and conditions of minimum manufacturing. Institute of Turkish Standards, 1999. [10] TS 2474. Determination of static bending properties of wood. Institute of Turkish Standards, 1976. [11] TS EN 310. Wood based panels—The determination of static bending strength and modulus of elasticity. Institute of Turkish Standards, 1999. [12] Bostro¨m L. Determination of the modulus of elasticity in bending of structural timber-comparison of two methods. Holz als Roh-und Werkstoff 1999;57:145–9.