CA1265031A - Structural glued-laminated timber - Google Patents
Structural glued-laminated timberInfo
- Publication number
- CA1265031A CA1265031A CA000487806A CA487806A CA1265031A CA 1265031 A CA1265031 A CA 1265031A CA 000487806 A CA000487806 A CA 000487806A CA 487806 A CA487806 A CA 487806A CA 1265031 A CA1265031 A CA 1265031A
- Authority
- CA
- Canada
- Prior art keywords
- pieces
- lumber
- bonding
- populus
- structural
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 241000219000 Populus Species 0.000 claims abstract description 43
- 238000000034 method Methods 0.000 claims description 33
- 238000001035 drying Methods 0.000 claims description 18
- 238000010030 laminating Methods 0.000 claims description 14
- 238000004519 manufacturing process Methods 0.000 claims description 14
- 239000000853 adhesive Substances 0.000 claims description 9
- 230000001070 adhesive effect Effects 0.000 claims description 9
- 210000001145 finger joint Anatomy 0.000 claims description 4
- 241000218979 Populus sp. Species 0.000 claims description 3
- 238000005304 joining Methods 0.000 claims description 2
- 239000000203 mixture Substances 0.000 claims 4
- 239000002023 wood Substances 0.000 abstract description 11
- 238000010276 construction Methods 0.000 abstract description 5
- 235000014466 Douglas bleu Nutrition 0.000 description 11
- 240000001416 Pseudotsuga menziesii Species 0.000 description 11
- 235000005386 Pseudotsuga menziesii var menziesii Nutrition 0.000 description 11
- 238000003475 lamination Methods 0.000 description 9
- 239000003292 glue Substances 0.000 description 7
- GHMLBKRAJCXXBS-UHFFFAOYSA-N resorcinol Chemical compound OC1=CC=CC(O)=C1 GHMLBKRAJCXXBS-UHFFFAOYSA-N 0.000 description 6
- 238000007796 conventional method Methods 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- 230000000007 visual effect Effects 0.000 description 3
- 241000183024 Populus tremula Species 0.000 description 2
- 238000004026 adhesive bonding Methods 0.000 description 2
- 230000003750 conditioning effect Effects 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 244000193510 Larix occidentalis Species 0.000 description 1
- 235000008122 Larix occidentalis Nutrition 0.000 description 1
- ISWSIDIOOBJBQZ-UHFFFAOYSA-N Phenol Chemical compound OC1=CC=CC=C1 ISWSIDIOOBJBQZ-UHFFFAOYSA-N 0.000 description 1
- 241000218657 Picea Species 0.000 description 1
- 239000005018 casein Substances 0.000 description 1
- BECPQYXYKAMYBN-UHFFFAOYSA-N casein, tech. Chemical compound NCCCCC(C(O)=O)N=C(O)C(CC(O)=O)N=C(O)C(CCC(O)=N)N=C(O)C(CC(C)C)N=C(O)C(CCC(O)=O)N=C(O)C(CC(O)=O)N=C(O)C(CCC(O)=O)N=C(O)C(C(C)O)N=C(O)C(CCC(O)=N)N=C(O)C(CCC(O)=N)N=C(O)C(CCC(O)=N)N=C(O)C(CCC(O)=O)N=C(O)C(CCC(O)=O)N=C(O)C(COP(O)(O)=O)N=C(O)C(CCC(O)=N)N=C(O)C(N)CC1=CC=CC=C1 BECPQYXYKAMYBN-UHFFFAOYSA-N 0.000 description 1
- 235000021240 caseins Nutrition 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000005553 drilling Methods 0.000 description 1
- 238000009499 grossing Methods 0.000 description 1
- 239000011121 hardwood Substances 0.000 description 1
- 238000003306 harvesting Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000002674 ointment Substances 0.000 description 1
- 238000012797 qualification Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 231100000241 scar Toxicity 0.000 description 1
- 241000894007 species Species 0.000 description 1
- 238000003892 spreading Methods 0.000 description 1
- 238000010561 standard procedure Methods 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 238000011179 visual inspection Methods 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B21/00—Layered products comprising a layer of wood, e.g. wood board, veneer, wood particle board
- B32B21/13—Layered products comprising a layer of wood, e.g. wood board, veneer, wood particle board all layers being exclusively wood
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
- B27M—WORKING OF WOOD NOT PROVIDED FOR IN SUBCLASSES B27B - B27L; MANUFACTURE OF SPECIFIC WOODEN ARTICLES
- B27M3/00—Manufacture or reconditioning of specific semi-finished or finished articles
- B27M3/0013—Manufacture or reconditioning of specific semi-finished or finished articles of composite or compound articles
- B27M3/006—Manufacture or reconditioning of specific semi-finished or finished articles of composite or compound articles characterised by oblong elements connected both laterally and at their ends
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B3/00—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form
- B32B3/02—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form characterised by features of form at particular places, e.g. in edge regions
- B32B3/06—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form characterised by features of form at particular places, e.g. in edge regions for securing layers together; for attaching the product to another member, e.g. to a support, or to another product, e.g. groove/tongue, interlocking
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
- B32B7/04—Interconnection of layers
- B32B7/12—Interconnection of layers using interposed adhesives or interposed materials with bonding properties
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Manufacturing & Machinery (AREA)
- Forests & Forestry (AREA)
Abstract
ABSTRACT
A structural glued-laminated timber is disclosed which is formed from wood derived from Poplar. Such timbers are useful in the construction industry as components of structural frameworks.
A structural glued-laminated timber is disclosed which is formed from wood derived from Poplar. Such timbers are useful in the construction industry as components of structural frameworks.
Description
6~3~
~2 This invention relates to wood products and, more particularly, to s~ructural glued-laminated timber.
The end use to which a wood product will be put is dictated largely by the in~egrity of the stock from which the product is fashioned. At one end of the spectrum of such products are those which are intended for use as structural members in construction of building frameworks.
To serve such a purpose, the construction industry requires a product of superior strength, capable of tolerating stresses in a variety of load-bearing environments.
Industry in Canada has met such demand by providing structural glued-lamina-ted timber or "glulam" which is a structural timber product obtained by bonding under pressure a number of graded pieces of laminating stock whose grain is essentially parallel. Presently, "glulams" are used in many types of constructions, including recreational buildings such as arenas and in residential, religious and industrial buildings.
Because glulams function as load-bearing members, one prime requirement is for the timber to be constructed from good quallty, superior strengtb lumber i.e. laminating stock. For this reason, glulams are almost exclusively made from laminating stock of Douglas fir although western larch f , j: . :, :. ~ . ~, . .... ,. ~.: : : . .
~a31 is occasionally employed. Lumber from su~h trees is generally recognized as superior as regards a number of grading parameters used in the art, including allowable stresses.
At the other end of the spectrum of wood products are those products which ~unction in essentially non-load-bearing environments including paper, waferboard and non-structural lumber. For economy, such products normally are manufactured from low grade wood which is abundantly available such as Populus s~ (Poplar), and the poorer grades of spruce. Wood from such trees is recognized in the art as plagued with knots, subject to warping and twisting particularly upon drying with attendant localized water deposits (in the case of Poplar) and low natural durability. Use of poplar, in particular, has been restricted to low grade products.
Presently, with continued depletion of Oouglas fir population and rising transportation cost, it is increasingly desirable to provide a s-tructural glued-laminated timber which provides the properties required of such a product but which is less costly.
It has now surprisingly been found that a good quality
~2 This invention relates to wood products and, more particularly, to s~ructural glued-laminated timber.
The end use to which a wood product will be put is dictated largely by the in~egrity of the stock from which the product is fashioned. At one end of the spectrum of such products are those which are intended for use as structural members in construction of building frameworks.
To serve such a purpose, the construction industry requires a product of superior strength, capable of tolerating stresses in a variety of load-bearing environments.
Industry in Canada has met such demand by providing structural glued-lamina-ted timber or "glulam" which is a structural timber product obtained by bonding under pressure a number of graded pieces of laminating stock whose grain is essentially parallel. Presently, "glulams" are used in many types of constructions, including recreational buildings such as arenas and in residential, religious and industrial buildings.
Because glulams function as load-bearing members, one prime requirement is for the timber to be constructed from good quallty, superior strengtb lumber i.e. laminating stock. For this reason, glulams are almost exclusively made from laminating stock of Douglas fir although western larch f , j: . :, :. ~ . ~, . .... ,. ~.: : : . .
~a31 is occasionally employed. Lumber from su~h trees is generally recognized as superior as regards a number of grading parameters used in the art, including allowable stresses.
At the other end of the spectrum of wood products are those products which ~unction in essentially non-load-bearing environments including paper, waferboard and non-structural lumber. For economy, such products normally are manufactured from low grade wood which is abundantly available such as Populus s~ (Poplar), and the poorer grades of spruce. Wood from such trees is recognized in the art as plagued with knots, subject to warping and twisting particularly upon drying with attendant localized water deposits (in the case of Poplar) and low natural durability. Use of poplar, in particular, has been restricted to low grade products.
Presently, with continued depletion of Oouglas fir population and rising transportation cost, it is increasingly desirable to provide a s-tructural glued-laminated timber which provides the properties required of such a product but which is less costly.
It has now surprisingly been found that a good quality
- 2 --: . :,. . ~ ~: . ., , , , .: .
~Z65il~3~
glulam can be manufacture~ from lumber obtained from Populus ~, despite the generally well-accepted understanding in the art that such wood has little or no value in such an application. Such a product is attractive in view of the abundance of available Poplar laminating stock.
Accordingly, the present invention provides a structural glued-laminated timber wherein the laminates are derived from Populus sp.
In another aspect of the present invention, there is provided a method of manufacturing structural glued-laminated timber which comprises selecting a plurality of pieces of lumber of laminate grade derived from PoPulus _~, each of said pieces defining a planar upper face and a planar lower face and laminating said pieces by bonding at the interface of respective lower and upper faces of adjacent piecesO
In a preferred embodiment of the process aspect of the invention, the individual pieces of lumber are formed by finger-jointing or scar~-jointing lumber members in the longitudinal direction.
The manufacture of glued-laminated timber from lumber
~Z65il~3~
glulam can be manufacture~ from lumber obtained from Populus ~, despite the generally well-accepted understanding in the art that such wood has little or no value in such an application. Such a product is attractive in view of the abundance of available Poplar laminating stock.
Accordingly, the present invention provides a structural glued-laminated timber wherein the laminates are derived from Populus sp.
In another aspect of the present invention, there is provided a method of manufacturing structural glued-laminated timber which comprises selecting a plurality of pieces of lumber of laminate grade derived from PoPulus _~, each of said pieces defining a planar upper face and a planar lower face and laminating said pieces by bonding at the interface of respective lower and upper faces of adjacent piecesO
In a preferred embodiment of the process aspect of the invention, the individual pieces of lumber are formed by finger-jointing or scar~-jointing lumber members in the longitudinal direction.
The manufacture of glued-laminated timber from lumber
- 3 -`
, ~ . , .. . ... ,. . . ., ~ - - . ... . - - . -.- :. :; - . , ,., , .~. : , ~3~L
of the Po~ e does not differ to any great extent in comparison to manufacture using Douglas fir lumber. The manufacturing standards for such timbers are well documented as outlined by the Canadian Standards Association in CSA
Standard 0122-M1980 en~itled "Structural Glued-Laminated Timber" and in CSA Standard 0177-Ml9~1 entitled "Qualification Code for Manufacturers of Structural-Glued Laminated Timber", published May, 1980 and November, 1981, respectively. Copies of the documents may be obtained by writing to 178 Rexdale Boulevard, Rexdale, Ontario, Canada M9W lR3.
Thus, in the case where Douglas fir lumber is employed as laminating stock, the requirements of glulam manufacture may be summarized as follows. Firstly, sawn lumber obtained after harvesting is graded as laminating stock by examining the entire length of the piece and assigned one of four grades depending on its characteristics particularly as regards stiffness but also including visual inspection for knots, checks, splits, slope of grain, wane, warp and pitch pockets.
It has been found that, like Douglas fir glulam, poplar glulam can be made from lumber of the required grade of any .
- ' ,~' . ,: . . . .
thickness, width and leng-th. In most cases, however, the lumber will have a nominal thickness of 2".
After grading, the lumber is dried to achieve a moisture content of not greater than lS~ and not less than 7%, the moisture content range of the pieces within one member being within 5%. Although Douglas fir lumber is easier to dry than poplar lumber, a number of drying procedures may be employed to attain poplar lumber having the desired moisture content. Poplar lumber tends to warp and degrade during drying and it is therefore preferable to use a strict drying regimen when the conventional method is used to manufacture poplar glulam. ~eterioration can be resisted by using the proper drying schedule in kiln drying and also by applying physical restraints to the package of lumber to resist warpage. In the following tables, Table I
defines a drying schedule for poplar lumber of 25 to 38mm thickness and Table II defines a schedule for poplar lumber of between 44 and 57mm thickness, which schedules are preferred according to the present invention:
~03~
TABr.E
For Conventional Drying of Aspen Poplar Lumber 1" to 1 1/2" Thick ~ood Moisture Temperature EMC (%) Content (~) Dry Bulb (C) Wet Bulb (C) Above 40 71.0 61.0 8.5 40 - 30 76.5 58.0 4.7 Below 30 82.0 54.5 3.0 Conditioning 82.0 77.0 12.6 Air velocity of 350 fpm (1.78 m/s) throughout For Conventional Drying of Aspen Poplar Lumber 1 3/4" to 2 1/4" Thick -Wood Moisture Temperature EMC (%) Content (~) Dry Bulb (C) Wet Bulb (C) Above 40 60.0 56.0 14.3 40 - 30 65.5 54.5 7.9 Belo~ 30 76.5 49.0 2.9 Conditioning 76.5 71.5 12.7 Air velocity of 350 fpm (1.78 m/s) throughout . . .
~2~
With respect to using restraints in the drying of poplar lumber, it has been found that top loaded weights ap~lied during kiln drying can be an effective means of reducing twist and such is preferred. A particularly preferred method of resisting deterioration during drying entails use of pinned and serrated stickers in maintaining straightness. In another preferred method, the package of lumber to be dried may simply be bound tightly to provide good results.
Once the wood has dried, all four faces are planed smooth to within tolerance guidelines (as set out in CSA
Standard 0122) and then graded, once again.
Grading is performed in two ways i.e. visually into four grades B-F, B, C and D, and by stiffness (modulus of elasticity). In the specific case of poplar glulam according to the present invention, it is preferred that only B-F, B and C grades of lumber which have been sawn no closer to the pith than 30mm be selected. By avoiding the pith of the harvested poplar in lumber of these grades as much as possible, the inherent poor quaIities of the tree may also be avoided to a desirable extent. D-grade lumber, containing some pith, may be used as lamstock provided that ~2~3~
its use is limited to the less-stressed, central portion of the glulam.
After visual grading, the stiffness of the dried pieces of lumber is evaluated according to procedures established in the art in order to exclude those pieces which do not comply with the standardized codes of manufacture. The most common procedure entails use of an "E-Rating machine" which applies a lateral force ~o the piece, the resistance to which is measured. The ~-value for each piece is used in conjunction with the visual grading characteristics of the piece to determine its final grade for use in glulam.
Because pieces of lumber are typically considerably shorter than the total length of the beam being manufactured, it is normally necessary, regardless of the origin of the lumber i.e. Douglas fir or Poplar, to make an end joint between lumber members of laminating stock to form a full length lamination. This can be achieved in two basic and well known ways i.e. by finger-joint or by scarf-joint.
In accordance with a preferred embodiment of the invention, the laminations in the lower one third of the timber i.e. in the highly tensile stressed laminations, are made using scarf-joints to add strength to the poplar glulam, whereas the remainder of the joints may be either of the scarf or the finger variety. Finger jointed pieces may be bonded at this stage of the process whereas it is preferred to delay bonding of the scarf-joints until later in the manufacturing process.
. , ~ ~ , ;
`' : ' `' . '.'' . ' :, .
~, . : ~ . . ,: , In a subsequent stage in the process, selected individual pieces of lumber or "laminating stock" are assembled together in a package but without any glue at their interfaces. By this procedure, pieces may be labelled according to grade and correctly located in the cross-section of the beam, in accordance with established guidelines. At this stage it must also be insured that end joints in the adjacent laminations are not stacked together but are separated from each other by some distance in the longitudinal direction.
The laminations are then taken in order and glue is applied with a spreader according to known procedures. rhe glue may be either a water resistant glue e.g. casein or a waterproof glue e.g. resorcinol~ Use of waterproof adhesives is preferred.
After spreading of the glue, the laminations are clamped along their length. Pressure may be applied in a number of standard ways. It has been found that a clamping pressure of about 150 lbs per square inch yields optimum bonding in poplar glulam and that a period of from 8 to 10 hours of pressure is preferred.
~2~;~3~
Because the process described above is based on conventional methods presently used in the industry, it is believed that such method will be most appropriate in producing poplar glularn on an industrial scale.
Nevertheless, other methods may be applied which are capable of producing the poplar glulam according to the present invention.
One alternative method is known as the "saw-dry-rip"
method. According to this process which is known generally in the art, Populus sp are harveste~ and brought to a saw mill where they are live sawn in the same plane into "flitches" i.e. longitudinal slices roughly 1 3/4" in width. A compact kiln load is created from the flitches and dried to a moisture content of about 10~ wherea~ter the flitches are again sawn longitudinally into pieces for laminating stock. The rernainder of the processing steps parallel those described above for the conventional method.
The saw-dry-rip method is more specific to the manufacture of hardwood for structural lumber and has the advantage that it reduces problems of excessive warp.
Another method for manufacturing poplar glulam according to the present invention is described in U.S.
:
: ., ., . " :, . ..
patent 3,985,169 to Chow entitled "Method of joining bodies of green lumber by finger joints". According to this procedure, fingers are cut on the ends of selecte~ lumber pieces and the lumber is then heated and dried such that the fingers only are drie~ to a moisture content of less than 50%~ The fingers are then cooled to prevent pre-cure of the glue-bond upon application of the adhesive following which the lumber pieces are pressed together at a pressure greater than 150 lbs per square incn to interlock the fingers until the adhesive has cured, which is accomplished by heat transfer in the pieces of lumber to the finger. A drying and heating temperature of greater than 59C is preferred as is the use of a heat-curable resin e.g. of the phenol~resorcinol type.
Final processing of the poplar glulam when manufactured according to any of the processes described usually includes the steps of smoothing surfaces of the bonded laminate to eliminate any irregularity in positioning of the laminations and remove any surface glue~ The laminate is then finished by drilling, notching etc. to accommodate any connection hardware required, coated with a coat "sealer" and wrapped in a package if required.
Thus, despite the general acceptance in the art that , :~
poplar lumber would not be appropriate as a wood for construction of structural glued-laminated timber, it has been found that such a product can be generated rrom poplar, the qualities of which compare with Douglas fir structural glulam. The laminates merely require appropriate selection according to established guidelines and according to those selective procedures described herein. Any species of poplar may be employed, of which tremuloides, balsamifera and ~randidentata are preferred. Use of cottonwood (trichocrapa and deltoides) is preferably avoided.
Example Poplar glulam was manufactured according to the method described below:
Logs of Populus sp. previously dried in an open-air environment for a period of about two years were sawn to provide lumber having a thickness of approximately 1.5", a width of approximately 5" and an approximate length of 12 feet.
Those pieces of lumber whose grade equalled or exceeded the D laminating grade specified in NLGA Standard Grading Rules for Canadian Lumber, 1978, published by the National . . . ~ ... ~ , ;
~ . ,, ,, :: ~, : .
- - : ~: . : - . . : .
,, ~ : :, ,, :
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Lumber Grades Authority, 1055 ~est Hastings Street, Vancouver, s.c., were selected for further processing.
Since the wood had drie~ naturally, adoption of kiln drying was not necessary, although the drying reyimen disclosed in Table l herein would otherwise have been employed.
Once graded, the lumber w~s planed to within acceptable tolerances and graded once again, both visually and in terms of "E-rating". Visual grading classified those pieces which could be identified as conforming to the requirements for grades B-F (bottom face or the extreme tension lamination), B,C and D pieces. The pieces were visually inspected further to ensure that none of the selected B-F, B and C
pieces contained pith. Thereafter, each of the selected pieces were "E-rated" for stiffness and selected according to established criteria.
While each of the selected pieces of lumber i.e.
"lamstock" were of equal and desired length, pieces were finger-jointed or scarf-~ointed using standard techniques to test the integrity of glulam containing such joints.
Accordingly, two glulams were pre-prepared using the dry lay-up step described previously, one of which comprised , - : ;
: :.. .
~650~
selective stacking of five pieces of finger-jointed lumber and the other of which comprised two lower pieces of scarf-jointed lumber upon which three finger jointed pieces were stacked. The testing of each of the samples, once fabricated, indicated that scarf joints should preferably be used in laminations stressed in tension higher than about 7MPa in order to produce a glulam surpassing required speciEications.
Once assembled, each package of pieces was disassembled to permit gluing which was performed only after insuring that the joints of respective pieces were staggered in the vertical direction. Gluing was conducted using waterproof resorcinol-based adhesive which was applied by roller spreader whereafter the laminate was clamped under pressure at 150 lbs per square inch Eor a time sufficient to allow the adhesive to cure.
The surface of the sides of th~ resultant timber were then smoothed and the entire surface of the beam was sealed.
Appearing below is a comparison of a poplar glulam made according to the present invention and a Douglas fir glulam:
::
.,~_ .. .. ... ..... :.. .. - ... - : . . .
-: : :. :
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: , , . ,:
TAsLE 3 Parameters Douglas Fir Poplar strength of 20f-E grade adequate adequate stiffness of 20f-E grade adequate adequate *development of drying stresses "normal" "better than Douglas fir"
cost per volume "unit" "lower than unit"
availability of raw material moderate & widespread &
decreasing & abundant localized * drying stresses result from the tendency of the interior of the piece to dry at a slower rate than the surfaces.
It can be seen from Table 4 that the poplar glulam provides a structural product having desirable properties.
Coupled with the reduced cost of Poplar in contrast with Douglas fir, the attributes of poplar glulam are attractive.
`:
,
, ~ . , .. . ... ,. . . ., ~ - - . ... . - - . -.- :. :; - . , ,., , .~. : , ~3~L
of the Po~ e does not differ to any great extent in comparison to manufacture using Douglas fir lumber. The manufacturing standards for such timbers are well documented as outlined by the Canadian Standards Association in CSA
Standard 0122-M1980 en~itled "Structural Glued-Laminated Timber" and in CSA Standard 0177-Ml9~1 entitled "Qualification Code for Manufacturers of Structural-Glued Laminated Timber", published May, 1980 and November, 1981, respectively. Copies of the documents may be obtained by writing to 178 Rexdale Boulevard, Rexdale, Ontario, Canada M9W lR3.
Thus, in the case where Douglas fir lumber is employed as laminating stock, the requirements of glulam manufacture may be summarized as follows. Firstly, sawn lumber obtained after harvesting is graded as laminating stock by examining the entire length of the piece and assigned one of four grades depending on its characteristics particularly as regards stiffness but also including visual inspection for knots, checks, splits, slope of grain, wane, warp and pitch pockets.
It has been found that, like Douglas fir glulam, poplar glulam can be made from lumber of the required grade of any .
- ' ,~' . ,: . . . .
thickness, width and leng-th. In most cases, however, the lumber will have a nominal thickness of 2".
After grading, the lumber is dried to achieve a moisture content of not greater than lS~ and not less than 7%, the moisture content range of the pieces within one member being within 5%. Although Douglas fir lumber is easier to dry than poplar lumber, a number of drying procedures may be employed to attain poplar lumber having the desired moisture content. Poplar lumber tends to warp and degrade during drying and it is therefore preferable to use a strict drying regimen when the conventional method is used to manufacture poplar glulam. ~eterioration can be resisted by using the proper drying schedule in kiln drying and also by applying physical restraints to the package of lumber to resist warpage. In the following tables, Table I
defines a drying schedule for poplar lumber of 25 to 38mm thickness and Table II defines a schedule for poplar lumber of between 44 and 57mm thickness, which schedules are preferred according to the present invention:
~03~
TABr.E
For Conventional Drying of Aspen Poplar Lumber 1" to 1 1/2" Thick ~ood Moisture Temperature EMC (%) Content (~) Dry Bulb (C) Wet Bulb (C) Above 40 71.0 61.0 8.5 40 - 30 76.5 58.0 4.7 Below 30 82.0 54.5 3.0 Conditioning 82.0 77.0 12.6 Air velocity of 350 fpm (1.78 m/s) throughout For Conventional Drying of Aspen Poplar Lumber 1 3/4" to 2 1/4" Thick -Wood Moisture Temperature EMC (%) Content (~) Dry Bulb (C) Wet Bulb (C) Above 40 60.0 56.0 14.3 40 - 30 65.5 54.5 7.9 Belo~ 30 76.5 49.0 2.9 Conditioning 76.5 71.5 12.7 Air velocity of 350 fpm (1.78 m/s) throughout . . .
~2~
With respect to using restraints in the drying of poplar lumber, it has been found that top loaded weights ap~lied during kiln drying can be an effective means of reducing twist and such is preferred. A particularly preferred method of resisting deterioration during drying entails use of pinned and serrated stickers in maintaining straightness. In another preferred method, the package of lumber to be dried may simply be bound tightly to provide good results.
Once the wood has dried, all four faces are planed smooth to within tolerance guidelines (as set out in CSA
Standard 0122) and then graded, once again.
Grading is performed in two ways i.e. visually into four grades B-F, B, C and D, and by stiffness (modulus of elasticity). In the specific case of poplar glulam according to the present invention, it is preferred that only B-F, B and C grades of lumber which have been sawn no closer to the pith than 30mm be selected. By avoiding the pith of the harvested poplar in lumber of these grades as much as possible, the inherent poor quaIities of the tree may also be avoided to a desirable extent. D-grade lumber, containing some pith, may be used as lamstock provided that ~2~3~
its use is limited to the less-stressed, central portion of the glulam.
After visual grading, the stiffness of the dried pieces of lumber is evaluated according to procedures established in the art in order to exclude those pieces which do not comply with the standardized codes of manufacture. The most common procedure entails use of an "E-Rating machine" which applies a lateral force ~o the piece, the resistance to which is measured. The ~-value for each piece is used in conjunction with the visual grading characteristics of the piece to determine its final grade for use in glulam.
Because pieces of lumber are typically considerably shorter than the total length of the beam being manufactured, it is normally necessary, regardless of the origin of the lumber i.e. Douglas fir or Poplar, to make an end joint between lumber members of laminating stock to form a full length lamination. This can be achieved in two basic and well known ways i.e. by finger-joint or by scarf-joint.
In accordance with a preferred embodiment of the invention, the laminations in the lower one third of the timber i.e. in the highly tensile stressed laminations, are made using scarf-joints to add strength to the poplar glulam, whereas the remainder of the joints may be either of the scarf or the finger variety. Finger jointed pieces may be bonded at this stage of the process whereas it is preferred to delay bonding of the scarf-joints until later in the manufacturing process.
. , ~ ~ , ;
`' : ' `' . '.'' . ' :, .
~, . : ~ . . ,: , In a subsequent stage in the process, selected individual pieces of lumber or "laminating stock" are assembled together in a package but without any glue at their interfaces. By this procedure, pieces may be labelled according to grade and correctly located in the cross-section of the beam, in accordance with established guidelines. At this stage it must also be insured that end joints in the adjacent laminations are not stacked together but are separated from each other by some distance in the longitudinal direction.
The laminations are then taken in order and glue is applied with a spreader according to known procedures. rhe glue may be either a water resistant glue e.g. casein or a waterproof glue e.g. resorcinol~ Use of waterproof adhesives is preferred.
After spreading of the glue, the laminations are clamped along their length. Pressure may be applied in a number of standard ways. It has been found that a clamping pressure of about 150 lbs per square inch yields optimum bonding in poplar glulam and that a period of from 8 to 10 hours of pressure is preferred.
~2~;~3~
Because the process described above is based on conventional methods presently used in the industry, it is believed that such method will be most appropriate in producing poplar glularn on an industrial scale.
Nevertheless, other methods may be applied which are capable of producing the poplar glulam according to the present invention.
One alternative method is known as the "saw-dry-rip"
method. According to this process which is known generally in the art, Populus sp are harveste~ and brought to a saw mill where they are live sawn in the same plane into "flitches" i.e. longitudinal slices roughly 1 3/4" in width. A compact kiln load is created from the flitches and dried to a moisture content of about 10~ wherea~ter the flitches are again sawn longitudinally into pieces for laminating stock. The rernainder of the processing steps parallel those described above for the conventional method.
The saw-dry-rip method is more specific to the manufacture of hardwood for structural lumber and has the advantage that it reduces problems of excessive warp.
Another method for manufacturing poplar glulam according to the present invention is described in U.S.
:
: ., ., . " :, . ..
patent 3,985,169 to Chow entitled "Method of joining bodies of green lumber by finger joints". According to this procedure, fingers are cut on the ends of selecte~ lumber pieces and the lumber is then heated and dried such that the fingers only are drie~ to a moisture content of less than 50%~ The fingers are then cooled to prevent pre-cure of the glue-bond upon application of the adhesive following which the lumber pieces are pressed together at a pressure greater than 150 lbs per square incn to interlock the fingers until the adhesive has cured, which is accomplished by heat transfer in the pieces of lumber to the finger. A drying and heating temperature of greater than 59C is preferred as is the use of a heat-curable resin e.g. of the phenol~resorcinol type.
Final processing of the poplar glulam when manufactured according to any of the processes described usually includes the steps of smoothing surfaces of the bonded laminate to eliminate any irregularity in positioning of the laminations and remove any surface glue~ The laminate is then finished by drilling, notching etc. to accommodate any connection hardware required, coated with a coat "sealer" and wrapped in a package if required.
Thus, despite the general acceptance in the art that , :~
poplar lumber would not be appropriate as a wood for construction of structural glued-laminated timber, it has been found that such a product can be generated rrom poplar, the qualities of which compare with Douglas fir structural glulam. The laminates merely require appropriate selection according to established guidelines and according to those selective procedures described herein. Any species of poplar may be employed, of which tremuloides, balsamifera and ~randidentata are preferred. Use of cottonwood (trichocrapa and deltoides) is preferably avoided.
Example Poplar glulam was manufactured according to the method described below:
Logs of Populus sp. previously dried in an open-air environment for a period of about two years were sawn to provide lumber having a thickness of approximately 1.5", a width of approximately 5" and an approximate length of 12 feet.
Those pieces of lumber whose grade equalled or exceeded the D laminating grade specified in NLGA Standard Grading Rules for Canadian Lumber, 1978, published by the National . . . ~ ... ~ , ;
~ . ,, ,, :: ~, : .
- - : ~: . : - . . : .
,, ~ : :, ,, :
" '' :-~3~
Lumber Grades Authority, 1055 ~est Hastings Street, Vancouver, s.c., were selected for further processing.
Since the wood had drie~ naturally, adoption of kiln drying was not necessary, although the drying reyimen disclosed in Table l herein would otherwise have been employed.
Once graded, the lumber w~s planed to within acceptable tolerances and graded once again, both visually and in terms of "E-rating". Visual grading classified those pieces which could be identified as conforming to the requirements for grades B-F (bottom face or the extreme tension lamination), B,C and D pieces. The pieces were visually inspected further to ensure that none of the selected B-F, B and C
pieces contained pith. Thereafter, each of the selected pieces were "E-rated" for stiffness and selected according to established criteria.
While each of the selected pieces of lumber i.e.
"lamstock" were of equal and desired length, pieces were finger-jointed or scarf-~ointed using standard techniques to test the integrity of glulam containing such joints.
Accordingly, two glulams were pre-prepared using the dry lay-up step described previously, one of which comprised , - : ;
: :.. .
~650~
selective stacking of five pieces of finger-jointed lumber and the other of which comprised two lower pieces of scarf-jointed lumber upon which three finger jointed pieces were stacked. The testing of each of the samples, once fabricated, indicated that scarf joints should preferably be used in laminations stressed in tension higher than about 7MPa in order to produce a glulam surpassing required speciEications.
Once assembled, each package of pieces was disassembled to permit gluing which was performed only after insuring that the joints of respective pieces were staggered in the vertical direction. Gluing was conducted using waterproof resorcinol-based adhesive which was applied by roller spreader whereafter the laminate was clamped under pressure at 150 lbs per square inch Eor a time sufficient to allow the adhesive to cure.
The surface of the sides of th~ resultant timber were then smoothed and the entire surface of the beam was sealed.
Appearing below is a comparison of a poplar glulam made according to the present invention and a Douglas fir glulam:
::
.,~_ .. .. ... ..... :.. .. - ... - : . . .
-: : :. :
.. -: . :
: , , . ,:
TAsLE 3 Parameters Douglas Fir Poplar strength of 20f-E grade adequate adequate stiffness of 20f-E grade adequate adequate *development of drying stresses "normal" "better than Douglas fir"
cost per volume "unit" "lower than unit"
availability of raw material moderate & widespread &
decreasing & abundant localized * drying stresses result from the tendency of the interior of the piece to dry at a slower rate than the surfaces.
It can be seen from Table 4 that the poplar glulam provides a structural product having desirable properties.
Coupled with the reduced cost of Poplar in contrast with Douglas fir, the attributes of poplar glulam are attractive.
`:
,
Claims (19)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Structural glued-laminated timber wherein the laminates are derived from Populus sp.
2. The structural timber according to claim 1 wherein the laminates are finger-jointed or scarf-jointed.
3. The structural timber according to claim 1 wherein the laminates are all scarf-jointed.
4. The structural timber according to claim 2 wherein the laminates are bonded by waterproof adhesive.
5. The structural timber according to any one of claims 2, 3 or 4 wherein the laminates are derived from Populus species is selected from tremuloides, balsamifera and grandidentata or mixtures thereof.
6. A method of manufacturing structural glued-laminated timber which comprises selecting a plurality of pieces of lumber of laminate grade derived from Populus sp, each of said pieces defining a planar upper face and a planar lower face and laminating said pieces by bonding at the interface of respective lower and upper faces of adjacent pieces.
7. The method according to claim 6 wherein said bonding is achieved with a waterproof adhesive.
8. The method according to claim 7 wherein the bonding is conducted under pressure of about 150 pounds per square inch.
9. The method to any one of claims 6, 7 or 8 wherein the Populus species is selected from tremuloides, balsamifera and grandidentata or mixtures thereof.
10. A method of manufacturing structural glued-laminated timber which comprises selecting a plurality of pieces of lumber of laminate grade derived from Populus sp each of said pieces defining a planar upper face and a planar lower face and laminating said pieces by bonding at the interface of respective lower and upper faces of adjacent pieces, wherein one or more of said pieces of lumber are constituted by individual lumber members joined longitudinally at their adjacent ends by finger-joint or scarf-joint.
11. The method according to claim 10 wherein said bonding is achieved with a waterproof adhesive.
12. The method according to claim 10 wherein the bonding is conducted under pressure of about 150 pounds per square inch.
13. The method according to claim 10 wherein the lowermost piece of lumber is scarf-jointed.
14. The method to any one of claims 11, 12 or 13 wherein the Populus species is selected from tremuloides, balsamifera and grandidentata or mixtures thereof.
15. A method of manufacturing structural glued-laminated timber which comprises drying a plurality of Populus sp lumber members to achieve a moisture range therein of between 7% and 15%, joining two or more of said members longitudinally at their adjacent ends by either finger-joint or scarf-joint to form a plurality of pieces of lumber, each of said pieces defining a planar upper face and a planar lower face, selecting from said plurality of pieces of lumber a plurality of laminate grade such pieces and laminating said pieces by bonding at the interface of respective lower and upper faces of adjacent pieces.
16. The method according to claim 15 wherein the lowermost piece of lumber is scarf-jointed.
17. The method according to claim 16 wherein said bonding is achieved with a waterproof adhesive.
18. The method according to claim 17 wherein the bonding is conducted under pressure of about 150 pounds per square inch.
19. The method to any one of claims 16, 17 or 18 wherein the Populus species is selected from tremuloides, balsamifera and grandidentata or mixtures thereof.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000487806A CA1265031A (en) | 1985-07-30 | 1985-07-30 | Structural glued-laminated timber |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000487806A CA1265031A (en) | 1985-07-30 | 1985-07-30 | Structural glued-laminated timber |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1265031A true CA1265031A (en) | 1990-01-30 |
Family
ID=4131093
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000487806A Expired - Lifetime CA1265031A (en) | 1985-07-30 | 1985-07-30 | Structural glued-laminated timber |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1265031A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102009031639A1 (en) * | 2009-07-03 | 2011-01-05 | Herbert Hagensieker Sägewerk GmbH | Glulam |
| US8245741B2 (en) | 2008-04-09 | 2012-08-21 | Les Chantiers Chibougamau Ltee | Method and system for glulam beams |
| WO2020252519A1 (en) * | 2019-06-18 | 2020-12-24 | Timberworks Industrial Group Pty Ltd | Engineered timber panel for structural use and method of formation thereof |
-
1985
- 1985-07-30 CA CA000487806A patent/CA1265031A/en not_active Expired - Lifetime
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8245741B2 (en) | 2008-04-09 | 2012-08-21 | Les Chantiers Chibougamau Ltee | Method and system for glulam beams |
| US8245742B2 (en) | 2008-04-09 | 2012-08-21 | Les Chantiers Chibougamau Ltee | Systems for glulam beams |
| DE102009031639A1 (en) * | 2009-07-03 | 2011-01-05 | Herbert Hagensieker Sägewerk GmbH | Glulam |
| WO2020252519A1 (en) * | 2019-06-18 | 2020-12-24 | Timberworks Industrial Group Pty Ltd | Engineered timber panel for structural use and method of formation thereof |
| CN114206568A (en) * | 2019-06-18 | 2022-03-18 | 木结构工业集团私人有限公司 | Engineered wood panels for structural use and methods of forming the same |
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