EP0351243A1

EP0351243A1 - An extendible structural beam

Info

Publication number: EP0351243A1
Application number: EP89307183A
Authority: EP
Inventors: Denis Leslie Mills
Original assignee: KENTEK Ltd
Current assignee: KENTEK Ltd
Priority date: 1988-07-14
Filing date: 1989-07-14
Publication date: 1990-01-17
Also published as: GB8816776D0

Abstract

An extendible structural beam 2 for use as a structural member especially in spaces where access is limited, and more particularly as a floor beam for use in loft conversions, comprises an elongate central member 4, and two elongate outer members 6, 8 which are slidably located within the end portions of, and project from, the central member 4. Each of the three members has a "C" shaped cross-section for ease of manufacture. The beam is tapered at 20 at each end to enable it to be fitted fully into the corner formed by a roof eave of a house, and wooden spacing pieces 22 are provided at each end for raising the level of the beam generally above the level of the wall plates. One or more capping strips 24 are provided on its upper surface. Warning bands 10 indicate excessive extension of the beam. The beam may also be used as a rafter, purlin or other structural support in a roof to replace or strengthen the existing roof structure.

Description

This invention relates to an extendible prefabricated structural beam for use as a structural member especially in spaces where access is limited, and more particularly as a floor beam in loft conversions or as a rafter, purlin or other structural support to replace or strengthen an existing roof structure.
Several types of floor beam are in use in industrial, commercial and residential premises. These range from those most commonly used, such as timber or steel beams of very simple cross-section, to beams such as "lattice beams" which comprise a lattice work of steel members usually capped top and bottom by a timber plate.
Known beams of the kind described above have the disadvantage that they are cumbersome to transport to, and utilise in, areas where access and space is limited, such as lofts. Further, they are usually supplied in standard lengths. Cutting such a beam to fit a non-standard dimension may be both difficult and awkward.
I have now designed an extendible, telescopic type, structural beam which can be extended, between defined minimum and maximum extensions, to any desired length. The beam has been designed to conform to the relevant British Standards whilst at the same time being comparatively light, easy and cheap to manufacture, and easy to use. It is intended that Do-It-Yourself enthusiasts and professional builders alike should be able to use the beam in loft conversion work. Use of this beam for this purpose requires no special access to be provided into the loft space, since the beam comprises portions which may easily be handled through even very small access hatches into the loft. The beam is designed so that it can be fitted in place above existing ceilings, thus obviating the necessity of removing the ceiling and ceiling joists prior to insertion of the beam.
According to the present invention I provide a structural beam comprising a plurality of members aligned along the same longitudinal axis which are slidable relative to each other in the direction of this longitudinal axis, and in which the outer end of each outermost member is tapered.
The angle, shape and nature of the taper may vary according to the shape of the spaces in which the beam is required to fit. For example, if the beam is a floor beam for use in loft conversions, the outer end of each outermost member is preferably tapered on an upper edge so as to fit in an eave of a loft. If the beam is a rafter for replacing or strengthening the existing roof structure, the two ends are preferably tapered such that one end can be mounted with its tapered edge substantially flush with a wall plate of a building, whilst the other end can be mounted with its tapered edge substantially flush with a roof ridge beam or with a tapered edge of a matching extendible beam employed for replacing or strengthening the opposing side of the roof. As used herein therefore, the term "tapered" connotes that less than preferably two thirds, more preferably less than one half and even more preferably less than one third of the depth of the end of the beam is untapered, and that the taper angle is preferably at least 30° with respect to the longitudinal axis of the beam, and typically in the range 40° to 50°.
Preferably, at least one of the members is of hollow box section. Preferably, at least one of the members is of substantially rectangular C-shaped cross-section. Preferably, each one of the members is removable from the member relative to which it is slidable.
Preferably, the structural beam comprises three slidable members, in which case it is preferred that it comprises an elongate central member and two elongate outer members, each respective outer member being slidably located within, and projecting from, an end of the central member.
Preferably, means is provided to indicate when the respective outer member has been extended beyond a safe limit. Said means may comprise a warning band on each outer member.
Preferably, a spacing piece is secured to the lower face of each outer member near its end, for raising the level of the beam generally above the level of its support points. Preferably, also, at least one capping strip is secured to the upper face of the beam.
A preferred embodiment of an extendible structural beam according to the invention is now described by way of example with reference to the accompanying drawings, in which:-

Figures 1a and 1b are side elevational views of the beam, without a capping strip, in its fully extended and fully closed states respectively.
Figure 2 is a cross-section to a larger scale through the central member of the beam, and
Figure 3 is a detailed perspective view of one end of the beam showing a timber spacing piece and capping strips fixed in place.

Referring to the drawings, Figures 1a and 1b show a general view of the extendible structural beam 2, which comprises a central member 4 from the ends of which project outer members 6, 8 respectively. The central member 4 and the outer members 6 and 8 are all manufactured by a cold forming process from galvanised steel sheet. A brightly coloured warning band 10 (any other warning mark could be provided) is permanently affixed to each of the outer members 6 and 8 and if either of these becomes visible, it is an indication to the installer that the respective outer member has been extended beyond its safe limit. This problem is solved by using a longer beam 4, 6 or 8. The warning band 10 may be marked on the members in alternative ways, such as painting. It is important for safety reasons that the marking is permanent.
For ease of transportation, the outer members 6 and 8 can be removed completely from the central member 4. This demountability feature makes the beam particularly amenable to being easily handled through even very small access hatches into, for example, a loft of a house.
As can be seen in Figure 2 the central member 4 is basically of rectangular C-shaped cross section, with arcuate corners. The outer members 6 and 8 are also of rectangular C-shaped cross section, but are so proportioned as to form a close-tolerance sliding fit within the central member 4. Both the central member 4 and the outer members 6 and 8 are designed so that they may be easily made from sheet metal by a cold forming process. As can be seen in Figure 3, the cut-out portion of the central member 4 is located at the bottom of the beam, whilst the cut-out portions of the outer members 6 and 8 are located at the top of the beam. Although this is the structurally optimal configuration, it will be appreciated that the cut-out portions could be located at the bottom of the beam instead of the top, or else at the sides of the beam.
Alternative materials, construction or manufacturing techniques and cross-sectional shapes are possible. For instance, a lightweight material such as aluminium would facilitate handling of the beam. Also, the members 4, 6 or 8 could be alternative cross-sectional shapes, such as a "G" shaped cross-section, or a box section. In the latter case, an alternative manufacturing technique such as an extrusion technique is preferred. However, the cross-sectional shape of Figure 2 in combination with the cold forming process of manufacture has significant advantages in terms of ease and cost of production.
The outer member 6 is a mirror image of the outer member 8, and hence only outer member 6 will now be described in detail. As shown in Figure 3, the outer end region 18 of the outer member 6 has its top corner removed so that the outer member 6 tapers as shown at 20, the taper angle being roughly 40° with respect to the upper face of the outer member 6, thus enabling the beam to be fitted fully into an eave of a loft. Although in this embodiment the taper angle is roughly 40°, alternative taper angles (for example, 30°, 45° or 60°) can be envisaged, dependent on, for instance, the pitch of the roof. A wooden spacing piece 22, such as a plate or wooden block, is releasably secured to the lower face of the outer member 6, near its end, to raise the beam above the level of the wall plate, on to which the wooden spacing piece 22 can be affixed. This lifts the beam clear of the ceiling below, which is important especially if it is of the "lath and plaster" construction, as this avoids the possibility of disturbing the ceiling. The ceiling, including the associated ceiling joists, may thus be left completely in tact.
The beam is completed for use by fitting wooden capping strips 24 to the upper faces of the various members, e.g. with self tapping screws. In this embodiment, the capping strips 24 are wooden, although many other materials (such as plastics materials) would also be suitable. The strip(s) 24 span virtually the entire length of the beam. The capping strip 24 on the outer member 6 is of slightly greater depth than that on the central member 4 to compensate for the slightly greater height of the central member 4, so that the upper faces of the capping strips 24 are substantially coplanar. The capping strips 24 enable floor boards or floor panels to be conveniently nailed in place.
Of course, a single capping strip 24 with a recessed central portion on its underside could be provided to span the entire length of the beam. Alternatively, if there is no requirement for perfect evenness in the floor boards or panels, these boards or panels could be attached directly to the beam without using a capping strip 24, or else all the capping strips 24 could be of the same depth.
It will be appreciated that the overall dimensions of the beam and thus its strength may be varied. For most practical purposes the required length of the beam is between 3 and 5 metres, whilst it is preferable to limit the length of individual members to no more than about 2 metres. With these restrictions, it may be necessary to provide a plurality of outer members 6 and 8 from which can be selected the most suitably sized member to fulfil a particular function. Capping strips 24 could be provided in standard lengths to be cut to the required length on site. A beam of the above dimensions is suitably 125 mm wide and 150 mm deep. Of course, a longer beam length, say 7 metres, can also be envisaged, the dimensions of the individual members being varied accordingly.
Although the beam has been described with particular reference to the problem of providing structural support for floors in lofts, it is envisaged that it could have more general usefulness wherever structural beams are required, especially in confined spaces. In particular, the beam could also be used as a rafter, purlin or other structural support in a roof to replace or strengthen the existing roof structure. For example, the beam could be mounted, using appropriate fixings and plates, with one end on the wall plate of a building and the other end against the roof ridge beam or else against one end of a matching extendible beam employed for replacing or strengthening the opposing side of the roof. Used in this way, the taper angle would be selected so as to provide a substantially flush fit with the surfaces against which the tapered edges are to be mounted.
It will thus of course be understood that the present invention has been described purely by way of example, and modifications of detail can be made within the scope of this invention. For example, the central member 4 could be sized to form a sliding fit within the outer members 6, 8, in which case two warning bands 10 would be affixed at appropriate places on the central member 4. As another example, instead of there being the warning band 10 to indicate when the beam has been extended beyond its safe limit, the extension of the beam could be limited by some form of limiting means, such as pegs affixed to each outer member 6 and 8 which would cooperate with a suitably dimensioned slot in the central member 4.

Claims

1. A structural beam comprising a plurality of members (4,6,8) aligned along the same longitudinal axis which are slidable relative to each other in the direction of this longitudinal axis, characterised in that the outer end of each outermost member (6,8) is tapered (at 20).

2. A structural beam according to claim 1 wherein at least one of the members is of hollow box section.

3. A structural beam according to claim 1 or 2 wherein at least one of the members is of substantially rectangular C-shaped cross-section (Fig.2).

4. A structural beam according to any one of claims 1-3 wherein each one of the members is removable from the member relative to which it is slidable.

5. A structural beam according to any one of claims 1-4 comprising three slidable members (4,6,8).

6. A structural beam according to claim 5 comprising an elongate central member (4) and two elongate outer members (6,8), wherein each respective outer member (6,8) is slidably located within, and projects from, an end of the central member (4).

7. A structural beam according to claim 6 wherein means (10) is provided to indicate when the respective outer member has been extended beyond a safe limit.

8. A structural beam according to claim 7 wherein said means (10) comprises a warning band on each outer member.

9. A structural beam according to any one of claims 6-8 wherein a spacing piece (22) is secured to the lower face of each outer member (6,8) near its end, for raising the level of the beam generally above the level of its support points.

10. A structural beam according to any one of the preceding claims wherein at least one capping strip (24) is secured to the upper face of the beam.