Box-shaped structural beam

Abstract

 The box-shaped structural beam, consists of two parallel hardwood beams positioned at a distance from one another constituting the top and bottom flange beams (1-2) of the structural beam, a wooden web plate (3-4) attached along each side of said flange beams so that a box-shaped structural beam is formed, a steel section (5) fastened parallel to the inside surface of at least one of the wooden flange beams (1-2) which is fully enclosed in the box-shaped structural beam, and stays (6-7) which serve to reinforce the whole fastened between the wooden flange beams and the steel section.

Description

[0001] The invention is for a reinforced box-shaped structural beam with a fairly long resistance to fire in the event of fire the construction of which is such that the height of the structural beam can be reduced to a minimum and the greatest possible span obtained.

[0002] Structural beams are known that consist of a single steel section and which are intended for the bearing structures of flat roofs in particular which are painted with fire-resisting paint in order to give the beams greater fire resistance and thus to prevent the rapid deformation and collapse of same as a result of the generated heat. A disadvantage of these is that the paint directly applied to the steel section does not remain fire resistant, making regular repainting necessary.

[0003] Also known is the enclosure of the steel section on the building site in a casing of fire-resisting panels, so that steel section is protected by said panels in the event of fire. The disadvantage of this implementation is that the installation on site of the fire resisting panels around the structural beams makes the structure as a whole rather expensive.

[0004] Another known implementation of structural beams consists of building these beams up from wooden strips which are glued together and are treated by a fire-resisting product. One disadvantage is that the beams must have relatively large dimensions for limited loads and large spans.

[0005] Structural beams are also known which are composed of two parallel beams positioned at a distance from one another and which are joined on each side and covered by a wooden web plate to form a closed box. This embodiment nonetheless has the disadvantage that the beam dimensions become too large for greater spans.

[0006] In order to counteract all the disadvantages of the various embodiments summarized above, a box-shaped structural beam has been realized in accordance with the leading characteristic of the invention consisting of two parallel hardwood beams positioned at a distance from one another which form the upper and lower flange beams of the structural beam, a wooden web plate attached along each side of said flange beams, so that a box-shaped structural beam is formed which is closed on the sides, a steel section fastened parallel to the inside surface of at least one of the wooden flange beams so that it is fully enclosed in the box-shaped structural beam, and stays inserted between the wooden flange beams and the steel section to strengthen the whole.

[0007] The combined effect of the material properties of the steel, hardwood and panel material make it possible to realize structural beams of a lower height than known box beams bearing an equal span and load. For relatively large spans of 20 meters and more the overall height of the structural beam may even be less than 1/25th of the span. Another advantage is that the steel components, such as the steel section and fastenings, which have little strength at higher temperatures in the event of fire, remain protected by the heat-insulating box enclosure. Another advantage is that the fire-resisting box-shaped structural beams can be entirely assembled in the workshop in advance thus enabling their cost to be reduced.

[0008] In the following a more detailed description of a possible embodiment of a box-shaped structural beam in accordance with the invention is given but without in any way being exhaustive. This description refers to the attached drawing where:

fig. 1 shows an installed box-shaped structural beam in accordance with the invention;

fig. 2 shows a plan view of same;

fig. 3 shows a cross-section of the structural beam along line III-III in figure 1, where the stays installed at an angle have been left out;

fig. 4 shows a vertical cross-section of the structural beam along line IV-IV of fig. 3.

[0009] From these figures it will be noted that the box-shaped structural beam designed for relatively large spans of 15 to 30 metres and with a fire resistance of a good 30 minutes is ideal for use as a structural beam for flat roofs. The structural beam comprises two parallel hardwood flange beams 1-2 positioned at a distance from one another and which form the upper and lower flange of the structural beam. Both flange beams should by preference be made from tropical hardwood and have high allowable stresses and moduli of elasticity. Both beams are joined on both sides by web panels 3-4 with fire-resisting properties and which are fastened by wire nails and/or screws and perhaps with glue to the beams in order to absorb longitudinal shear forces, to form a closed box-shaped structural beam. These web panels may consist for example of plywood panels, chipboard panels or other suitable panels. All the said fastening elements are installed so that they are recessed and then covered with fire-resisting compound. The selected embodiment of the structural beam makes use of a single steel section 5 which is firmly attached to the lower side of the upper flange beam 1 by means of wood screws. To strengthen the whole vertical and inclined wooden stays 6-7 are installed between both flange beams 1-2 and the steel section 5 to absorb transverse forces. These vertical and inclined stays 6-7 are fastened by means of zinc-coated steel corner elements 8, wire nails, bolts and/or glue to the flange beams 1-2 and the steel section 5, where the corner pieces can also be welded to the steel section. In this way all the steel components such as the steel section 5, the corner elements 8 and the fastening elements, which have little strength when exposed to the high temperatures of a fire, are encased and protected in the heat-insulating structural beam. In order to obtain a fire resistance of 30 minutes or more, an additional thickness of material 9 is provided on the lower and upper flange 1-2 and on both web panels 3-4. The dimensions of said thickness are determined in relation to the ignition speed of the selected material. For example if "Azobe" wood (red iron wood) is the material selected for flange beams 1-2 and "Class 1" fire-resisting panels are used as the web panels, the upper surface of the top flange beam 1, the lower surface of the bottom flange beam 2 and the web panels 3-4 are made 15 mm thicker so that a fire resistance of 30 minutes is obtained. After thirty minutes of burning the structural beam will after being reduced by 15 mm still offer sufficient strength to bear the loads for which it was designed. Openings can also be allowed between stays 6-7 for the passage of cables and pipes. From the foregoing it is clear that the combination of the enclosed steel section 5 attached to a hardwood flange beam results in a strong and more fire-resistant box-shaped structural beam whereof the height can be made less than that of existing structural beams, so that their price can be reduced.

[0010] It goes without saying that the nature, dimensions and shape of the constituent parts described and of the box-shaped structural beam thus formed may differ depending on the desired objective.

Claims

1. Box-shaped structural beam, characterized by the fact that it consists of two parallel hardwood beams positioned at a distance from one another constituting the top and bottom flange beams (1-2) of the structural beam, a wooden web plate (3-4) attached along each side of said flange beams so that a box-shaped structural beam is formed, a steel section (5) fastened parallel to the inside surface of at least one of the wooden flange beams (1-2) which is fully enclosed in the box-shaped structural beam, and stays (6-7) which serve to reinforce the whole fastened between the wooden flange beams and the steel section.

2. Box-shaped structural beam in accordance with claim 1, characterized by the fact that the steel section is fastened to the flange beam (1) by wood screws.

3. Box-shaped structural beam in accordance with claim 1, characterized by the fact that the flange beams (1-2) are made of tropical hardwood provided with additional material (9) in order to acquire fire resistance.

4. Box-shaped structural beam in accordance with claim 1, characterized by the fact that the web panels (3-4) consist of panel material with fire-resisting properties and are provided with additional material (9) in order to acquire fire resistance.

5. Box-shaped structural beam in accordance with claim 1, characterized by the fact that the stays (6-7) are made of wood and are fastened by means of metal corner pieces (8), fastenings, and welds between the flange beams (1-2) and the steel section (5).

6. Box-shaped structural beam in accordance with claims 2 and 5, characterized by the fact that all the fastenings employed such as screws and wire nails are recessed and covered with a fire-resisting compound.

7. Box-shaped structural beam in accordance with claim 1, characterized by the fact that openings are provided between the stays (6-7) for the passage of pipes and cables.

Drawing