AU708316B2

AU708316B2 - Laminated timber product and method

Info

Publication number: AU708316B2
Application number: AU39191/97A
Authority: AU
Inventors: Bruce Bell
Original assignee: LAMINATED TIMBER SUPPLIES Pty
Current assignee: LAMINATED TIMBER SUPPLIES Pty Ltd
Priority date: 1996-09-24
Filing date: 1997-09-24
Publication date: 1999-07-29
Anticipated expiration: 2017-09-24
Also published as: AU3919197A

Description

LAMINATED TIMBER PRODUCT AND METHOD The present invention relates to a laminated timber product and more particularly to a laminated timber product for use in exterior or outdoor structural applications. Accordingly, the laminated timber product of this invention is a structural member which is to be installed and have its service-life outdoors. The present invention also relates to a method of forming such a laminated timber product.

Timber products used in structural applications outdoors must not only be structurally sound and mechanically rated for their load bearing role, they must also be durable. That is, they must be resistant to attack from conditions such as decay fungi organisms which can cause the timber to rot as well as subterranean termites. Both of these adverse conditions may be present in the outdoor service environment for the product. If the timber is susceptible to attack from either one •the structural integrity of the timber can be compromised, particularly where the 0 15 structural member has a service life of several years.

Before many known timbers are used in outdoor applications, they are treated with chemical preservatives such as copper chromium arsenate (CCA) or light organic solvent petroleum (LOSP) to achieve a maximum "Class 1") durability rating required by law. Treatment of laminated timbers, such as radiata 4 pine, with CCA involves coating or immersing the individual elements of each lamination or layer prior to bonding the layers to form the final product. Treatment with LOSP typically involves coating the whole final product to provide a protective envelope around the timber. It would be advantageous if these forms of chemical treatment were unnecessary, not only because they entail additional processing of the timber but also because the chemicals involved are undesirable from an ecological viewpoint.

The callitris species of native Australian conifers produce very durable timber. Callitris glauca and callitris columellaris, both generally known as white cypress pine, are the main commercial species. The heartwood of white cypress pine is naturally resistant to attack by subterranean termites and decay fungi organisms. However, the sapwood of white cypress pine (hereinafter also simply "cypress") is not, although it is resistant to lyctus borer.

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3 The very durable nature of the natural cypress heartwood makes it suitable for outdoor use, for example as fence post poles. As the trunk of a mature cypress tree has a relatively small diameter however, the creation of larger timber products (eg. benchtops or beams) from this wood requires lamination of a collection of smaller elements. While it may be desirable to use only heartwood in laminated cypress products to be used outdoors, the typical trunk dimensions and the way the timber is cut would mean excessive waste and expense to create the product without any of the less durable sapwood. That is, it would be both wasteful and less economical to eliminate all sapwood from the product.

It is an object of the present invention to provide an improved laminated timber product which has a high durability making it suitable for outdoor use without the need for chemical preservative treatment of the timber. It is also an too object of this invention to provide an improved timber product which is engineered for load bearing in a structural application.

to: 15 According to one aspect, the present invention provides a laminated timber product for an outdoor service-life in a structural application comprising a plurality of timber elements arranged in adjacent and substantially parallel layers extending t longitudinally of the product and including two outermost layers and at least one inner layer between the two outermost layers, each of the layers being adhesively 20 bonded to an adjacent layer at abutting surfaces of the timber elements of the 9 adjacent layers, the plurality of timber elements being comprised of white cypress pine and including cypress heartwood and cypress sapwood, wherein the timber .I elements of the outermost layers comprise substantially only heartwood and the sapwood content of the timber elements of the at least one inner layer is such that, in any full cross-section of the product taken perpendicular to the longitudinal extent of the layers, the sapwood does not exceed 10 percent of the crosssectional area and does not extend across the full width of the product.

According to another aspect, this invention provides an elongate laminated timber structural member for outdoor installation and service-life including a plurality of timber elements arranged in adjacent layers, said layers extending longitudinally of the member and including two outermost layers at opposite sides of the member and at least one inner layer therebetween, and each of the layers

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being adhesively bonded to an adjacent layer at a face joint between abutting surfaces of the timber elements of the adjacent layers; wherein the timber elements are white cypress pine, the timber elements of the outermost layers comprising substantially only cypress heartwood and the timber elements of the at least one inner layer including cypress sapwood such that, in any full cross-section of the member taken perpendicular to the longitudinal extent of the layers the sapwood does not exceed 10 percent of the cross-sectional area and does not extend across the full width of any face joint.

One of the benefits of cypress timber is that, when cut, the sapwood is readily distinguishable from the heartwood by its distinctly lighter colour. When laying up the timber elements in their layers or laminations to create a new laminated timber product therefore, it is possible to visually discriminate where in the product and in what proportions the sapwood is to be included.

Each layer or lamination of the product may be formed from several timber e 15 elements joined end-to-end in end joints or side-by-side in side joints, or both, so as to extend the full width and length of the laminated timber product. End joints are preferably in the form of intermeshing wedges finger joints). End joints occurring in adjacent layers are desirably located out of alignment with each other.

That is, the end joints of adjacent layers preferably do not occur in a same cross- S 20 section taken perpendicular to the layers of the product.

In at least one preferred form of this invention each of the outermost layers of the product are mechanically proof graded to ensure satisfactory mechanical properties. For example, the timber elements of the outermost laminations may undergo non-destructive testing to satisfy a minimum allowable modulus of elasticity Young's Modulus).

Before being combined to form the laminated product, the timber elements are dried or cured to a moisture content in the range of 11 to 15 percent of dry timber mass. The moisture content is typically about 12% and this is preferably achieved by a slow air-drying process with timber elements of relatively small section size. Rapid drying of cypress timber tends to produce undesirable surface checking and splitting.

The glue formulation used to create the adhesive bond between the timber elements of the laminated timber product includes a resorcinol or phenol- C:WINWORD\KATE\PRO/\LAMTIM.

DOC

resorcinol type resin as a primary component providing for relatively "cold" curing at temperatures in the range of 20-45 degrees Celsius. The bonding achieved with the resorcinol based glue formulation is desirably enhanced by the addition of tannin. Tannin is a naturally occurring compound which can be obtained from the bark of wattle trees, such as the mimosa wattle. The tannin can be blended with some (though not all) resorcinols to produce more stable and longer lasting gluelines at the end joints and face joints of the product. Tannin is preferably included by an amount of at least 5 percent of the total mass of the glue formulation mixture used. The higher the quantity of tannin added, the higher the curing temperature required for the glue formulation. For example, with a percent tannin composition a desirable curing temperature is approximately 300C. However, for a tannin composition of around 40 percent the curing temperature will more desirably be about 45 0 C. Caustic soda solution is also :desirably added to glue formulation in an amount of 20-40 ml per 5 kg of the glue 15 mixture.

According to a further aspect, the present invention provides a method of forming an elongate laminated timber structural member for outdoor installation and service life, including the steps of: selecting a plurality of white cypress pine timber elements; arranging the plurality of timber elements in adjacent layers extending longitudinally of the structural member and including two outermost layers and at °•.least one inner layer therebetween such that the outermost layers include substantially no cypress sapwood and sapwood content of the at least one inner layer is such that in any full cross-section of the member taken perpendicular to the longitudinal extent of the layers the sapwood does not exceed 10 percent of the cross-sectional area and does not extend across the full width of the product; applying a glue formulation between the timber elements; and adhesively bonding the timber elements together by holding the elements firmly together and applying heat to the structural member over a period of time sufficient for the glue to properly cure.

Thus, this invention provides a white cypress pine laminated timber product, and a production sequence for manufacturing same, which is suitable for outdoor use in structural applications without the need for treatment with

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preservative chemicals. That is, the invention provides a predictable and uniquely durable timber product. The timber product of this invention has the further advantages that it is hardwearing, has the decorative and aesthetically appealing appearance of natural cypress colours, can be readily painted if desired, and has good nail-holding properties. The occurrence of large and small knots is also a characteristic of this cypress timber. Typically the knots are tight knots which do not readily fall out of the sawn wood.

The present invention is therefore concerned with providing laminated timber structural members such as beams, columns and posts which are adapted to endure the adverse conditions of the environment outdoors. The structural members of the invention will usually be elongate with a rectangular section and the timber elements which make up each member will also typically be elongate and of rectangular section. Accordingly the beams, columns, posts and other members formed in accordance with the invention will be suitable for use in oo: 15 outdoor structures such as bridges, buildings, gazebos and pergolas. In yet oo another aspect, therefore, the present invention provides a structural frame for outdoor service life which includes a laminated timber product or structural member as described above.

A preferred embodiment of this invention is hereafter described by way of 20 illustrative example with reference to the accompanying drawing figures wherein like reference characters designate like features and wherein: Figure 1 is a side view of a portion of a laminated timber product according to an embodiment of the invention; and Figure 2 is a view of a cross-section of the laminated timber product of Figure 1 taken in the direction of arrows X-X.

Referring to Figure 1 and Figure 2, the present invention provides a laminated timber product 1 in the form of an elongate structural member adapted for outdoor installation and service life. The product 1 comprises a plurality of white cypress pine timber elements 2 arranged in adjacent and substantially parallel layers or laminations 3 which extend longitudinally of the product 1. The layers 3 include two outermost layers 4 located at opposite top and bottom sides of the structural member and a plurality of inner layers 5 located between the two outermost layers 4. Each of the layers is adhesively bonded with a resorcinol C\WINWORD\KATE\PROV\AMTI1M

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based glue formulation to an adjacent layer at a face joint 6 between abutting surfaces of the timber elements 2 in the adjacent layers.

The white cypress pine timber elements 2 all include cypress heartwood while some also include cypress sapwood 7. The timber elements 2 of the outermost layers 4 include substantially no sapwood 7. That is, the outermost layers comprise only cypress heartwood. In addition, the timber elements 2 of these outermost layers 4 are mechanically proof-graded in a non-destructive test to ensure that they satisfy the mechanical properties required for the designated structural role of the product 1. The sapwood 7 is present in one of the inner layers 5 and is readily distinguishable from the heartwood by its lighter colour. As can been seen in Figure 2, the cypress sapwood 7 does not extend across the full width W of the face joint 6 and accounts for less than 10 percent of the cross-sectional area shown.

end joint 8 is clearly visible in Figure 1 where a pair of timber elements 2 15 within a layer 3 are joined in end-to-end relationship. The respective ends of the joined timber elements are formed with complimentary intermeshing wedges to form of a typical finger joint. Some larger and smaller knots 9 which are a characteristic of white cypress pine are also clearly visible in Figure 1.

The method of forming the laminated timber product 1 shown in Figure 1 S* 20 and Figure 2 comprises the steps of selecting a plurality of the white cypress pine timber elements 2 and arranging those elements in adjacent layers 3 which extend substantially longitudinally of the product such that the outermost layers 4 include substantially no cypress sapwood and such that sapwood content of the inner layers 5 does not exceed 10 percent of the cross sectional area in any crosssection of the product taken perpendicular to its longitudinal extent. The timber elements are also arranged so that the sapwood 7 does not extend across the full width of the product.

The method also includes preparing a resorcinol or phenol-resorcinol based glue formulation including at least 5 percent by mass of wattle tannin. The wattle tannin, such as mimosa wattle tannin, is usually supplied in a dry powder form.

The wattle tannin is dissolved in warm or hot water and the tannin solution obtained should then be allowed to cool before it is combined with the resorcinol type resin.

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The tannin solution and resorcinol are blended in the desired portions. To that basic resin formulation may also be added small amounts of soda ash or caustic soda solution to improve the curing process.

It is important to note that the tannin solution will not be compatible with all resorcinol glue formulations. The tannin solution will simply not blend smoothly with some resorcinols, so some trial and experiment may be required to select a compatible resorcinol. BordenTM RS240M resin is an example of a resorcinol resin that is compatible with wattle tannin.

The blended glue formulation is then applied between each of the timber elements 2 which are then held together under clamping pressure and adhesively bonded by curing the glue through the application of heat to the clamped timber ~elements over a period of hours. With glue formulations having a tannin .composition of about 5 percent by mass, the desirable curing temperature is about 300C with a curing time of 2 to 3 hours. A lower curing temperature of about will suffice, but a longer curing time of 4 to 5 hours will be required. Where the tannin composition is around 40 percent by mass, a higher curing temperature of about 450C is suitable.

The gluelines of the clamped product 1 are typically heated to their curing temperature by exposing the product to heated air in a heating chamber. With relatively low tannin levels the gluelines may also be heated by radio waves in an RF (radio frequency) curing process.

is to be understood that various modifications, alterations and/or additions S• "may be introduced into the method of performance or the construction and arrangement of the parts previously described without departing from the spirit or ambit of the present invention.

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THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A laminated timber product for an outdoor service-life in a structural application comprising a plurality of timber elements arranged in adjacent and substantially parallel layers extending longitudinally of the product and including two outermost layers and at least one inner layer between the two outermost layers, each of the layers being adhesively bonded to an adjacent layer at abutting surfaces of the timber elements of the adjacent layers, said plurality of timber elements being comprised of white cypress pine and including cypress heartwood and cypress sapwood, wherein the timber elements of the outermost layers comprise substantially only heartwood and sapwood content of the timber elements of the at least one inner layer is such that in any full cross-section of the product taken perpendicular to the longitudinal extent of the layers the sapwood does not exceed 10 percent of the cross-sectional area and does not extend 15 across the full width of the product.

2. A laminated timber product as claimed in claim 1, wherein at least one of said layers includes two or more of said plurality of timber elements joined end-toend in end joints so as to extend the full length of the laminated timber product.

3. A laminated timber product as claimed in claim 2, wherein each end joint is formed from a plurality of complementary intermeshing wedges cut at a joining end of the respective timber elements.

4. A laminated timber product as claimed in claim 2 or claim 3, including more than one end joint with at least one end joint located in adjacent layers, wherein the end joints of adjacent layers are located out of alignment such that they do not occur in a same cross-section of the product taken perpendicular to the longitudinal extent of the layers.

A laminated timber product as claimed in any one of the proceeding claims, wherein each layer includes timber elements joined side-by-side in side joints so as to extend the full width of the product.

6. A laminated timber product as claimed in any one of the proceeding claims, wherein the moisture content of the plurality of timber elements as a percentage of the dry mass of the timber is in the range of 11 to 15 percent.

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Claims

7. A laminated timber product as claimed in any one of the proceeding claims, wherein the plurality of timber elements are adhesively bonded together using an adhesive including a resorcinol or phenol-resorcinol type resin blended with tannin.
8. A laminated timber product as claimed in claim 7, wherein the adhesive includes tannin in an amount of at least 5 percent by mass of the total adhesive mixture.
9. A laminated timber product as claimed in claim 7 or claim 8, wherein the tannin is a wattle tannin.
10. An elongate laminated timber structural member for outdoor installation and service-life including a plurality of timber elements arranged in adjacent layers, said layers extending longitudinally of the member and including two outermost layers at opposite sides of the member and at least one inner layer therebetween, .*:and each of the layers being adhesively bonded to an adjacent layer at a face joint between abutting surfaces of the timber elements of the adjacent layers; wherein the timber elements are white cypress pine, the timber elements of the outermost layers comprising substantially only cypress heartwood and the timber elements of the at least one inner layer including cypress sapwood such that in any full cross-section of the member taken perpendicular to the longitudinal 20 extent of the layers the sapwood does not exceed 10 percent of the cross- sectional area and does not extend across the full width of any face joint. o .11. A structural member as claimed in claim 10 wherein the plurality of timber elements are adhesively bonded together using a resorcinol and tannin based glue formulation.
12. A structural member as claimed in claim 11 wherein the glue formulation includes tannin by an amount of at least 5 percent by mass of the total glue formulation.
13. An elongate laminated timber structural member substantially as hereindescribed with reference to the accompanying drawings.
14. A structural frame adapted for an outdoor service life including a laminated timber product as claimed in any one of claims 1 to 9 or a structural member as claimed in any one of claims 10 to 13. C:\WINWORDWVIOLET\PHILJODELETE\AMTIMNDOC 11 A method of forming a laminated timber structural member for outdoor installation and service life, including the steps of: selecting a plurality of white cypress pine timber elements; arranging the plurality of timber elements in adjacent layers which extend longitudinally of the structural member and include two outermost layers and at least one inner layer therebetween such that the outermost layers include substantially no cypress sapwood and sapwood content of the at least one inner layer is such that in any full cross-section of the member taken perpendicular to the longitudinal extent of the layers the sapwood does not exceed 10 percent of the cross-sectional area and does not extend across the full width of the member; applying a glue formulation between the timber elements; and adhesively bonding the timber elements together by holding the timber elements firmly together and applying heat to the member over a period of time sufficient for the glue formulation to properly cure. DATED: 9 April, 1999 PHILLIPS ORMONDE FITZPATRICK Attorneys for: LAMINATED TIMBER SUPPLIES PTY LTD C:\WNWORD\VIOLET\PHIL\NODELETEAMTIMN.DOC ABSTRACT An elongate laminated timber structural member for outdoor installation and service-life including a plurality of timber elements arranged in adjacent layers The said layers extend longitudinally of the member and include two outermost layers at opposite sides of the member and at least one inner layer therebetween. Each of the layers is adhesively bonded to an adjacent layer at a face joint between abutting surfaces of the timber elements of the adjacent layers. The timber elements are of white cypress pine and in the outermost layers comprise substantially only cypress heartwood. The timber elements of the at least one inner layer include cypress sapwood such that in any full cross-section of the member taken perpendicular to the longitudinal extent of the layers the sapwood does not exceed 10 percent of the cross- sectional area and does not extend across the full width of any face joint. o o a.* a. a a. C:\WINWORD\KATE\PROV\LAMTIM.DOC