The invention relates to a connecting element for joining of building elements, such as boards, plates or the like together on both sides of the connecting element for forming a double-sided construction, such as a sandwich-construction.

Double-sided constructions, such as double-walls and the like have previously been mounted by a method, in which the building elements, such as boards or plates are mounted on both sides of the connecting elements acting as the supporting structure by securing the elements on the connecting elements from outside with fixing means such as spikes or screws. Building up the constructions by this method is time consuming, and it is difficult to perform the task in a mechanically operated manner. Demounting the constructions is cumbersome as well, and the fact that the spikes or screws remain fastened to the support structure or the building elements causes difficulties .

ith the aid of the connecting element in accordance with the invention, the double sided structure can be mounted quickly and, when desired, also in a mechanized manner. For achieving this purpose, the connecting element comprises holding surfaces on its opposite sides, the holding surfaces being interconnected by a connecting portion, which maintains the holding surfaces in spaced relationship. The holding surfaces are provided with

spikes, nails, prongs or the like projecting from the surface and acting as means for attaching the building elements to the opposite sides of the connecting element. These features give the connecting element the advantageous properties, that a separate securing stage is no more needed, when the construction is mounted. The building elements can be simply compressed onto the connecting elements after they have been properly placed with respect to the connecting elements. After the possible demounting of construction, the spikes or the like remain in the connecting elements, which is one advantageous feature of the invention.

According to a preferred embodiment, the connecting element is constituted of plate-like portions, so that on the opposite sides of the element there are plate like portions, which are interconnected by a plate-like connecting portion, the outer surfaces of the plate like portions acting as a holding surface for attachment of the building elements. This kind of connecting element can be easily manufactured to a profile element by bending plate like material into a suitable shape.

Further, according to a preferred embodiment, the opposite sides of the connecting element are each constituted of a separate element, which is joined to the opposite element by means of fixing members for forming the said connecting portion between the holding surfaces. In this case the both sides of the double-sided structure can be built up as separate part, which are joined together with fixing members

of the separate elements of the connecting element to constitute a combined construction with the combined connecting element therein. The separate elements can be for example profile elements comprising one or several adjacent portions having a substantially U-shaped cross section, the portions comprising planar portions 4 comprising the holding surface and adjoining to the edge of the U-shaped profile. The said profile elements can be directly connectable to each other with fixing means incorporated therein or via a separate joining piece, in which case the joining piece and/or the profile element can be provided with means for locking them to each other.

The invention will be described in more detail hereinafter by reference to the accompanying drawings, wherein

Fig 1 is a perspective view of the connecting element in accordance with the invention,

Fig 2 is a cross-sectional view of the connecting element of fig 1,

Fig 3 shows various shapes of the connecting element according to the invention as cross-sectional views and

Fig 4 is a perspective view of the structure of a double wall built up by means of the connecting element according to the invention.

Figs 1 and 2 show one preferred embodiment of the connecting element in accordance with the invention. The connecting element is constituted of two parallel elongate profile elements 1, which are interconnected by means of a joining piece 2 . The profile element comprises a portion 3 having a U-shaped cross-section. To the both edges in the opening direction of U, planar portions 4 are joined, one to each edge. The surfaces of these planar portions facing the opening direction of U form holding surfaces 5, which are provided with spikes 6 projecting substantially perpendicularly out of the planar surface. The function of these spikes 6 is to become embedded in the building elements for fastening of the building elements onto the holding surfaces 5. Both holding surfaces 5 of the profile element 1 lie substantially in the same plane, and the plane extends substantially parallelly with the plane defined by the similar holding surfaces 5 of the profile element 1 on the opposite side of the connecting element. The bottom portion of the U-shaped portion of the profile element is planar and extends parallelly with the aforementioned planes.

The profile elements 1 are combined to a complete connecting element by means of joining pieces 2 . The joining piece 2 is constituted of plate like portions comprising two portions 7 having each a similar U-shaped cross-section and opening at opposite directions, i.e. the inner surfaces of the U shapes are turned away from each ^' other facing towards opposite directions. The U-shaped portions are fixedly joined together at their bottom parts through

a web portion 8. Each profile element 1 is connected to the joining piece 2 so that the inner surface of each U-shaped portion 7 faces the correspondingly shaped outer surface of the U-shaped portion 3 of the profile element 1. The securing between the joining piece and the profile elements is brought about by fixing means formed therein. On the outsides of the U-shaped portion 3 of the element there are openings 9 and in the U-shaped portion 7 of the joining piece there are portions 10 elevating from its inner surface and positioned to coincide with the positions of the openings 9 in the profile element. When the U-shaped portions 3 and 7 of the profile element and the joining piece respectively are pressed against each other, the elevated portions 10 coincide with the openings 9 and click into said openings due to the resiliency of the U-shaped portion 7 of the joining piece and interlock the joining piece and the profile element to each other.

At the end of the connecting element there are arranged flanges 11 folded outwards from the U-shaped portions 3 of the profile elements 1 and extending perpendicularly to the longitudinal axis of the connecting element. The purpose of these flanges is to receive the pressure directed on the connecting element by the building structures perpendicular to the connecting element, such as the pressure caused by roofing constructions.

The profile elements and the joining pieces constituting the connecting element can be manufactured easily of steel plates, for example of

zinc-coated steel. The manufacture can be carried out for example by bending with the conventional working methods. The spikes 6 of the holding surfaces 5 can be formed by punching up in a known manner. The spikes can be disposed in a regular pattern, for example in groups depending on the properties and the structure of the building elements and the required strenght of the construction. The elevated portions 10 projecting out of the inner surface of the U-shaped portion 7 of the joining piece can be formed in a simple manner by punching a slit to the plate material and bending the portion of the plate material adjacent to the slit so that the other edge of the slit together with a small portion is elevated and projects out of the rest of the plate material.

The joining piece can be formed easily out of two metal plates bent into a suitable shape and being symmetrical to each other in a mirror-image manner. The plates are fixedly joined to each other so, that the planar portions facing each other in the connecting area of the plates together form the web portion 8 interconnecting the U-shaped portions 7 of the joining piece. For improving the thermal insulation the joining piece can be manufactured of a suitable material having good insulating properties, such as wood or plastics. In this manner, the cold bridges in the double-sided structure contributing to heat losses are avoided. For this purpose, for example a intermediate board element can also act as a joining piece, the profile elements being joined each on one side thereof.

The length of the joining piece in the longitudinal direction of the connecting element can constitute only a small portion of the total lenght of the connecting elements. In this case several joining pieces can be arranged along the lenght of the element at equal intervals.

The profile elements 1 and the joining pieces 2 can be combined to a connecting element by pressing the U-shaped portions 3 of the profile elements against the correspondingly dimensioned portions of the connecting pieces 2. The joining can be thus made in a simple and a quick manner. The combined connecting element can also be demounted without causing damages to its structure and the re-use of the parts of the connecting element is thus possible.

By means of the spikes 6 projecting out of holding surfaces 5, a firm securing of the building elements to the connecting element is obtained, because the spikes can be shaped in such a manner, that they penetrate to the element and become firmly embedded therein. If there is a need to contemporarily demount the constructions during the building operation or later, this can be done in a simple manner for example by wedging a suitable tool into the space between the U-shaped portion of the profile element and the building element. When demounting the construction, no separate nails remain in the building elements, and the connecting elements are not damaged, which improves the re-usability of the various elements of the demounted construction.

Fig 3 shows cross-sectional views of connecting elements according to the invention having various shapes. The elements are elongated profile elements manufactured of metal plate by bending and comprising at their opposite sides holding surfaces 5 disposed in spaced parallel relationship and having spikes 6 projecting therefrom. The holding surfaces are interconnected by a straight, plate-like connecting portion 12. The connecting element can have a Z-shaped (fig 3a), C-shaped (fig 3b) or I-shaped (fig 3c) cross-section or its cross-section can also have a shape of the separate profile element 1 shown in fig 2 in which the holding surfaces 5 on the same side of the element are formed of parallel surfaces of planar portions folded from the edges of the U-shape portion and the holding surface on the opposite side is constitued of the bottom surface of the U-shaped portion facing a direction opposite to the opening direction of U (fig 3d). The aforementioned connecting element can have also two or several adjacent U-shaped portions with the aforementioned planar portions interconnecting the U-shaped portions (fig 3e) . In all aforementioned embodiments, a good bending stiffnes of the connecting element acting as the supporting structure is obtained against all directions .

Fig 4 shows a double-sided wall construction built up with the aid of the connecting elements according to the invention. The elongate boards 13 are assembled transversely relative to the connecting element to a wall on opposite sides of the connecting element 14. Several connecting elements can be disposed at equal

intervals along the horizontal direction of the wall. The boards can be secured to the connecting element by pressing with a suitable press machine. In the case, where the connecting element is constituted of separate elements, which can be joined to each other, the both sides of the double wall can be assemblied separately and attached together for example at the building site.

The invention is described hereinabove only referring to some advantageous embodiments thereof. It will be understood, that the invention can be applied in various ways within the scope of the claims. The shape of the cross-section of the connecting element can be also different to those represented by the Figures. The elongated connecting element can be straight along its longitudinal axis or it can also be curved for obtaining a suitable construction with curved surfaces.

The invention is well suited for assembling constructions of all kinds of building elements, such as boards and plates and also of various raw-materials, such as wood or other suitable material, such as gypsum. A construction having an appearance similar to that of a conventional wall made of logs can also be built up with the aid of connecting elements by assembling suitably shaped planks on both sides of the connecting elements. The connecting element is suited also for assemblying other doubl-a-sided constructions in addition to the constructions forming parts cf buildings. " ese include for example similar structures used in fences and bridges.