Constructional element, structural element thereof, and method for the manufacture of such elements

The present invention concerns a construction-structural element suitable for assembly to a constructional element intended for cogging/notching as well as a method for the manufacture of such a structural element. The invention also concerns a constructional element assembled of such structural elements as well as a method for the manufacture thereof. According to another aspect the invention concerns use of such structural elements.

Background It is an old tradition to notch buildings with timber logs. In recent years this tradition has mainly been upheld with respect to building of cabins/ leisure buildings. Cabins with cogged joints are generally seen to be particularly beautiful. Building with this tradition is, however, not free of problems.

A disadvantage with notching of cabins/ buildings in real timber is the high requirement of premium quality timber. Such timber is today a scarce resource and the buildings therefore become expensive. Another disadvantage is the thermal insulation capability. Compared to well insulated buildings of modern construction, the thermal insulation is significantly poorer. In a Nordic climate, log houses (notched houses) that are not provided with an internal insulation is not suited for use all year, and is quite uneconomical also for cabin use.

A third disadvantage is related to the fact that buildings in timber logs sinks several centimetres per meter of height the first years, which leads to severe problems with respect to maintaining tight doors that do not get jammed and to maintain leakage free roof openings for pipes and ventilation. On this basis and on the basis of a need for a more extensive use of recycle material in building production, attempts have been made with respect to make a constructional element that looks like real timber but consists of an internal, insulated core and a surrounding wooden or wood-like "shell".

Norwegian patent No. 311 583 describes timber-like elements for notching where each side of the elements is comprised by several (e.g. 3) joined panel elements that are profiled in a manner so that their outer sides subsequent to the joining appear as substantially continuous, convex surfaces. Between these joined panel elements spacer elements are arranged that serve to hold the panels in a steady, unchanged mutual distance from each other. The same spacer elements serve to give the entire building its required strength. The void between the outer parts is intended to be filled with a thermally insulating material,

e.g. polyurethane. Near the ends the elements are provided with recesses for notching. The construction has the disadvantage that preparing and assembling of each timber-like element from individual panels and spacers is a comparatively complex process.

Swedish laid-open publication No. 457 456 describes a "timber-element" with outer tree panels provided with longitudinal groves, where the spacers are arranged in the groves. The void between the panels and the spacers are also in this construction intended to be filled with a thermally insulating material like foamed polyurethane. Holes are arranged in certain positions of the spacers so that rods 8 may be positioned (vertically) through the holes in each element of a completed wall, whereby said rods may constitute the weight carrying elements of the wall. Like for the construction discussed above, this construction comprises a lot of components that need to be adapted to each other and it is quite a "puzzle" work to put together one single timber element from its separate components.

US patent No. 4,433,519 describes a hollow, cylindrical prefabricated constructional element intended for the same use as the above mentioned publications. Here it is assumed that the convex outer surfaces are comprised either by glass fibre, metal, plastic or moulded wooden products with the required structural integrity. The outer panels are thus not made in a natural wooden material. Flanges at the upper and lower side of the constructional elements are arranged to overlap when the elements are placed on top of each other, and they are provided with holes so that bolts or the like may be inserted through the elements to lock the elements together. Like the previously discussed constructions this one also comprises spacer elements that are arranged at certain intervals along the elements, but here the prefabricated elements themselves are designed to carry most of the weight load. The void between the elements is preferably filled with a thermally insulating material. This construction has the advantage over the previous ones that it is assembled from fewer components but on the other hand the side panels are not in "whole wood".

Swedish laid-open publication No. 440 250 describes still another product intended for notching, and it constitutes outer wooden panels with inner spacers that are attached to the side panels by means of longitudinal grooves in the latter. The wooden panels according to this publication do not comprise a convex outer surface. It is mentioned, however, that the edges may be chamfered to give a visual impression of such a convex surface.

Swedish laid-open publication No. 303 580 describes a notching log in a sandwich construction comprising side walls of tree- or log-like design (panel boards) which are firmly attached to one another via an intermediate insulating layer of foam plastic and optionally a waterproof layer between the panel board constituting the inside wall and the foam plastic. During manufacture the foam plastic is moulded to the panel boards so that they obtain the required rigidity and strength to maintain their shape and carry the logs above in an entire

assembled wall.

Norwegian patent No. 318 394 describes a constructional element suitable for notching with outer, curved surfaces or walls made of whole three panels or the like and which on their inside are provided with a plastic layer that aided by internal ribs serves to stabilize the constructional element and which also serves as a moisture barrier for the constructional element. A method for the manufacture of such constructional elements is provided, comprising application of the mentioned plastic layer in an extruder. It is however a disadvantage with this constructional element that the plastic material is comparatively combustible and also quite expensive. Objectives

It is an object of the present invention to provide a structural element for a constructional element as well as a constructional element assembled from such structural elements as well as a method for the manufacture of such elements, which in a completed assembled condition looks like notched logs to a degree of confusion. It is thus an object to provide a structural element and constructional element respectively which have curved outer sides in "whole wood" or corresponding material, which can be manufactured in a quick and efficient process.

It is furthermore an object of the present invention to provide a constructional element as mentioned which have sufficient space to accommodate all required insulation in an internal void and which easily can be filled with a conventional insulating material before or after assembly.

It is furthermore an object to provide a structural element and constructional element respectively of said type which also are fire resistant or just slightly combustible.

It is furthermore an object to provide a structural element as mentioned which is useful for rehabilitation of existing buildings.

It is still further an object to provide a structural element and constructional element respectively as mentioned which may readily be disassembled to recycle components after use.

The invention The said objectives are fulfilled by a constructional element and its method of manufacture as described below.

According to a first aspect the present invention comprises a structural element according to claim 1 and a method for the manufacture thereof as defined by claim 13. According to another aspect the present invention concerns a constructional element comprised by two

connected structural elements of the first aspect of the present invention, as defined by claim 6 and a method for the manufacture thereof as defined by claim 14.

Preferred embodiments of the invention are disclosed by the dependent claims.

Below the term "construction-structural element" or "structural element of a constructional element" is generally used about the first aspect of the invention as defined by claim 1 , or the simplified form "structural element".

It is a central element of the present that the components making up the constructional element are assembled in a simple, efficient process which may largely be automatized. It is further a central element that this is achieved without sacrificing aesthetical aspects of the product which preferably has outer surfaces in whole wood.

The boards can optionally be provided with grooves on their surfaces facing inwards to thereby making them more flexible and to allowing them to be curved with no visible crack formation.

It is furthermore especially preferred that the side walls are based on solid (whole) wood but other materials can be used as well. It is also possible to use one type of material for an outer sidewall of a constructional element to be used in an outer wall and a different material for the inner side wall. In a corresponding manner different materials can be used for two sides of a constructional element intended for a partition wall, e.g. a wall between a living room and a kitchen. Normally, however, the same material is used for both sides of a constructional element according to the present invention, which is also the simplest with respect to production and logistics.

It is furthermore possible to use a simpler type of side wall, e.g. one without curved surface on the internal wall if the impression of timber logs is not an issue and one rather prefers to have a flat surface that may be covered with wall paper or the like. In such a case a construction-structural element according to claim 1 is used in combination with elements or plates that are not part of the present invention. It is thus a central part of the present invention that the construction-structural element according to claim 1 also is intended for applications other than being combined to a log-like constructional element according to the second aspect of the invention. As an example the construction-structural element according to the present invention can be used as internal or external panel, with or without use of insulating material, with attachment to a flat wall surface, to nailing strips or to vertical furring strips with per se known attachment means.

Specific embodiments of the invention

Below the invention is described in more detail with reference to the enclosed drawings, in which

Figure 1 is a cross-sectional view of a constructional element according to the present invention, comprising two structural elements according to the present invention.

Figure 2 is another cross-sectional view of the constructional element shown in Figure 1.

Figure 3 shows in perspective a part of a constructional element as shown in figures 1 and 5 2.

Figure 4 a-f shows in perspective several steps of manufacture of a structural element according to the invention by means of a rotary press adapted to the purpose.

Figure 5 shows use of the structural elements one-by-one as a panel for a flat wall surface.

Figure 1 shows a cross-section of a constructional element 2 according to the present 10 invention comprising two structural elements facing each other so that the cross-section of the constructional element has a generally convex shape, mainly corresponding to a log shaped for notching. The outer surface of each structural element comprises of a solid wooden board 3 in a single piece, curved to a desired shape in a manner as described more in detail below. To the inside of each board 3 a support plate 4, curved to the shape 15 of the board and covering substantially the entire inner surface of the board, is attached with glue. The plate 4 is in a material suitable for providing torsional support and load carrying capacity to the structural element and thereby to the constructional element while also fulfilling requirements to fire resistance.

To the inside of the support plate 4 stiffening ribs 5 are attached at certain intervals for

20. stabilizing the curvature of the board 3 and the support plate 4. By allowing the ribs 5 to have a vertical extension (height) corresponding to the width of the support plate 4 and the board 3 in the curved condition, the ribs may also carry loads vertically when the constructional element 2 or structural element 1 as such are assembled to a wall or in a wall. Figure 1 shows spacing tenons or plugs 7 being attached in holes in respective

25 oppositely arranged ribs 5 of two structural elements 1 , so that pairs of ribs are connected and a constructional element is formed. The constructional elements 2 can also be connected in other manners or additional manners in stead of or in addition to the shown spacer plugs 7 and can comprise insulation, recesses for electric cables or other types of cables or conduits as well as guiding sleeves for vertical tensioning rods as discussed in

30 Norwegian patent No. 318 394. Such tensioning rods can at their lower end be anchored in a foundation wall and will contribute to maintaining the integrity of a completed wall, i.a. so that the constructional elements are not permitted any mutual movement regardless of the wind to which the wall surface is exposed. The ribs may be made in various materials but it is preferred that they are made from wood which is inexpensive and stable even

35 under varying temperature conditions.

Figure 2 shows a cross-section of a constructional element as shown in Figure 1 but between two pairs of oppositely arranged ribs. The otherwise empty space between the two mutually connected structural elements is typically filled with an insulating material 9. It may be a discontinuous insulating material or a solid plate-shaped insulating material with a certain shape. Solid insulating material has the advantage that it is generally easier to recover/ recycle on disassembly of a constructional element. At the inside of the support plate 4 there may, dependent on the actual application, be arranged a particularly fire resistant plate 6. Such a plate may e.g. be made in gypsum and shaped (moulded) with the same curvature as the support plate 4. Such a plate will not bind easily to other materials with glue and is partly for this reason discontinuous in the length direction of the structural element where the ribs 5 are glued to the support plate 4. Such fire resistant plate 6 may be arranged to the inside of one or both structural elements 1 according to the invention when these are assembled in pairs to constructional elements 2. In Figure 2 a fire resistant plate 6 is shown only adjacent to the leftmost structural element 1. Figure 3 is a perspective view of a limited extension of a constructional element according to the invention as shown in cross-sectional view in Figures 1 and 2. The longitudinally extending lines at the side of the board are only intended to emphasize the curved shape of the board and do not represent any kind of joint or splice. A tape 10 or the like which will be hidden in an assembled state, closes the top of the constructional element 2. Figures 4a-f show in perspective, and in a number of procedural steps, segment of a rotating press 11 which is used to manufacture the structural element 1 according to the first aspect of the present invention. The press 11 comprises an extended pressing head 12 which can rotate around an axis 15 and is provided with two sets of pressing irons 13a and 13b at opposite sides of the pressing head 12. The pressing irons 13a and 13b have an outer shape which are convex with a curvature that corresponds to the desired curvature of the structural elements to be manufactured and which also corresponds to a concave curvature of a press mould 14 arranged beneath the press head 12 and constitutes another part of the rotating press 11. The pressing irons 13a, 13b are discontinuous in the length direction of the pressing head or provided with recesses at certain positions for reception of ribs 5 therein, cf. Fig. 4a. When ribs 5 are placed in such recesses, cf. Fig. 4b, the convex side of the ribs 5 are level with the convex side of the pressing irons 13a and 13b respectively.

Figures 4a and 4b illustrate how a set of ribs 5 (in practice much more than two) are arranged from above and down into the intervals between pressing irons 13a to be temporarily fixed therein. Ribs are moved downwards from above in a mainly straight movement. Figure 4c shows how the pressing head is thereafter rotated 180 degrees around the axis 15 so that the pressing irons 13a and the ribs 5 are facing the press mould

14. In the mean time a board 3 and a support plate 4 have been placed on the press mould 14 which also carries a certain flexible plate 16 with sturdy side flanges 17 along both side edges. The board 3 and/ or the support plate 4 are at this point in time also furnished with a film of glue at their relevant sides. Also the ribs 5 may be provided with a layer of glue at their convex side.

The flexible plate 16 is made in a material with a high tensional strength, such as spring steel. The distance between the side flanges 17 is accurately adapted to the width of the board 3 so that the flanges, when the board is bent, will absorb much of - or all of - the forces arising at the outside of the board being bent; such forces being tensional forces which in the absence of such a plate with side flanges would lead to uncontrolled crack formations in the board 3. The adaptation of the distance between the side flanges in relation to the width of the board 3 makes it possible to ensure just a limited crack formation or no crack formation at all in the board 3.

In Figure 4c a beginning rotation of the pressing head 12 is shown and in Figure 4d the pressing head has been rotated 180 degrees so that the pressing irons 13a and the ribs 5 in between these are facing the press mould 14 below. In Figure 4e the pressing is conducted by forcing the press mould with a high force up against the press head 12 so that the elements therein between, namely a board 3, a support plate 4 and a flexible plate 16, are all bent to the common curvature of the ribs 5, pressing irons 13 (a or b) and press mould 14. One might also, in addition to or in stead of raising the press mould, lower the pressing head 12. When a predetermined pressure is obtained, such pressure is maintained for a desired period of time so that glue between the layers intended to be glued together, is allowed to form a durable glue joint. The glue to be used can be any type of suitable industrial glue, such as but not limited to phenolic glue or melamine urea- formaldehyde glue.

Already prior to initiating the pressing or while it is conducted, a new set of ribs 5 can be placed between the pressing irons 13b facing upwards.

In Figure 4f the pressing head 12 is again separated from the press mould 14 while the structural element 1 comprising a board 3, support plate and ribs 5 is left on the press mould 14. The structural element 1 is resting on the flexible plate 16 which has the ability to reassume a plane shape when no longer exposed to pressure.

While a typical use of the structural element is that of connection in pairs to form constructional elements for notching, it is also highly relevant for use one by one in rehabilitation and/ or weatherising of houses. In the latter case the structural elements are typically used as horizontal panel and furnished with end elements having the shape of the external part of a cog joint, as shown in Figure 5. The structural elements can be attached

to a flat wall or to typically vertical attachment members in the form of furring strips or nailing strips mounted for the purpose. Additional insulation can desirably be placed in between such vertical attachment members. When the attachment is correctly made there is no visible difference between from the convex side of a wall surface where the structural elements 1 are used one by one and one that is notched by constructional elements 2 made from pairs of structural elements 1.

The use of the present invention in the form of structural elements connected in pairs to constructional elements has some obvious similarities with Norwegian patent No. 318 394 and a number of features mentioned in this previous patent, such as use of tensional rods to stabilize the walls, are also applicable with the elements of the present invention. The major differences between the present invention and said patent lies in the methods of manufacturing, which are completely different and the use of less expensive and more fire resistant materials in case of the present invention as well as improved recyclability.

When it is stated that a number of ribs are arranged at mutually defined intervals, this normally means that there is a fixed mutual distance between the ribs though there might in terms of production be possible to find other embodiments that function nearly as well.

With respect to the cogging joints, these are preferably not made as an integral part of the constructional elements of the present invention. Instead each constructional element is terminated with an open recess designed to cooperate with separate cogging elements of the type described in Norwegian patent No. 318 394.

In relation to use of separate cogging elements, each constructional element is with respect to its manufacture terminated as mentioned above, with an open end facing the cogging joint. To this open end a prefabricated transitional element may typically be attached, said transitional element not being part of the present invention and may be of many different types, such as e.g. the one described in Norwegian patent No. 320 956.

Terminations of walls against windows and doors are typically made with a sealed end- piece which is not part of the present invention. Such end-pieces are generally discussed in Norwegian patent No. 318 394 but other ways to terminate the constructional elements are also feasible. It is worth noticing that on delivery from factory to a construction site the constructional elements of the present invention will normally already be provided with end-pieces and/ or transition elements as described in Norwegian patent No. 318 394, alternatively separate cogging elements where such elements are intended. The constructional elements according to the present invention do not, however, comprise such further elements. The list of advantages with the present invention is long:

Firstly the production is simple and may easily be automatized and it is therefore inexpensive.

Secondly the constructional elements have excellent fire resistant properties when the support plate is chosen in a suitable material, such as e.g. plywood, which is confirmed by tests performed by the Norges Branntekniske laboratorium (Norwegian Fire Safety Laboratorium).

Thirdly the structural elements are as such immediately recyclable as woodwork. Also combined constructional elements may easily be split in two and be recycled. When insulation is used in the form of solid plates these also may be easily recycled. Fourthly the elements walls have - at least preferably - a curved shape that to the degree of confusion looks like log timber.

Fifthly the elements are lightweight, approximately one third of the weight of timber and still form a strong wall/ construction when assembled. Only one third of the wood is used compared to the building of log houses and the quality of the woodwork is less critical. Sixthly it is easy to achieve excellent insulation without any risk of cold bridges through the constructional element.

In addition the production can easily be adapted/ readjusted so that an architect designed cabin or the like can be included in the controlling program (CAD/CAM) which automatically calculated and effectuates production of the correct number of accurately dimensioned and numbered constructional elements. The constructional elements can then be delivered as a complete do-it-yourself kit with an accompanying instruction-CD explaining step by step how the kit is best assembled.