EP0051445B1

EP0051445B1 - A floor grating

Info

Publication number: EP0051445B1
Application number: EP81305104A
Authority: EP
Inventors: Owen Lyell Livingston
Original assignee: OWEN LYELL LIVINGSTON
Current assignee: OWEN LYELL LIVINGSTON
Priority date: 1980-10-28
Filing date: 1981-10-28
Publication date: 1985-09-11
Also published as: AU550546B2; EP0051445A2; JPH0149864B2; JPS57108358A; EP0051445A3; NZ198765A; AU7685981A; ATE15456T1; DE3172255D1

Abstract

The invention discloses a method of forming gratings suitable for use as walkways etc. The method includes the steps of forming transverse bearer bars (1) from strips of flat plate by punching a series of transverse slots across the central axis of each plate, then folding the plates to form U-sections with the slots located in the apices of the U-sections. Longitudinal bars, which are lengths of flat bar, are then inserted as tight press-fits into the slots, and the undersides of the longitudinal bars are deformed laterally between the legs of each U-section to prevent their removal from the slots. A strong lightweight grating results.

Description

Field of the Invention

This invention relates to floor gratings which are suitable for supporting substantial loads off the ground, and to gratings formed by the method. In particular, the invention relates to gratings of the type having two sets of parallel bars extending at right angles to one another to form a load supporting grid arrangement. Such gratings are commonly used in elevated walkways etc.
In this specification, the two sets of bars will be referred to as longitudinal and transverse bars respectively, but this is not to be taken in any way as limiting the direction in which either set may extend in an assembled grating.

Background to the Invention

It has already been proposed to use inverted U-shaped members for the transverse bars (see US-A-1,620,8461, with slots being cut in the apices of these members to receive portions of the longitudinal bars. In United States Patent No. 1,620,846, the preferred shape of the longitudinal bars is a square section. According to that patent, once a series of transverse bars have been arranged in parallel with their slots aligned, the longitudinal bars are dropped loosely into the slots to form a grid. The slots are made deep enough to receive the full height of the longitudinal bars.
Once in position in the slots, the longitudinal bars are deformed outwardly in those regions lying between the legs of the U-shaped transverse bars to prevent their removal from the slots. The transverse bars are also deformed above the longitudinal bars to provide further insurance against withdrawal from the slots.
There are a number of problems associated with the manufacture of a grating of the type disclosed in USP 1,620,846. In this patent, the inverted U-shaped members are formed by forcing the legs of an angle section member toward one another. In view of the substantial strength of most standard angle sections available, this operation is not easily achieved. The difficulty is increased in that standard angle sections have a finite radius in the fillet of the section which provides some resistance to bending the legs of the section towards one another.
Another problem is encountered in the provision of the slots in the apices of the transverse members. It is suggested in US-A-1,620,846 that this be achieved by a lateral punching operation, or by cutting. It will be appreciated that the fillet of the angle section will provide resistance to this operation as well. The very nature of the angle section renders the punching operation at the apex a difficult one.
Deformation of the longitudinal bars is achieved by means of a pressing operation. The bed plate of the press used is shaped to deform the transverse bars in the region of the edges of the slots to cause these edges to overlap the longitudinal bars which have been received in the slots. Such deformation has the effect of reducing the compressive strength of the upper edges of the transverse bars. Furthermore, the fact that the whole depth of the longitudinal bars is received within the slots formed in the transverse bars means that the uppermost edges of the steel of the transverse bars are unable to take any compressive loading at all, since there is no continuity of material above the level of the longitudinal bars.
A further disadvantage of the grating described in US-A-1,620,846 lies in the protection of the grating against corrosion once it has been fabricated. Sharp bends etc. should be avoided if galvanising or painting operations are contemplated, to ensure that a uniform coating is achieved. The deformation employed in the grating shown in the US specification will give rise to sharp edges at the sides of the slots, and consequently to difficulty in applying the necessary coating to these critical areas of steel to protect it.
Nevertheless, the use of U-shaped transverse members has been shown to have certain advantages as regards weight savings. It is accordingly an object of the present invention to provide a method of manufacture for a grating employing such members, which method does not suffer from the disadvantages set out above in respect of the known gratings.
The invention provides a floor grating which has a plurality of inverted, U-shaped transverse bars and a plurality of longitudinal bars, the longitudinal bars locating in slots formed in the apices of the transverse bars and being deformed in those regions lying within the U-shapes, characterised in that the longitudinal bars are flat bars which are press-fits in the slots, in that the transverse bars are formed by folding them from flat plate, in that the longitudinal bars are deformed without cutting into the material of the longitudinal bars so that their depth is substantially the same in those regions lying within the U-shapes as in those regions lying outside the U-shapes, and in that pairs of adjacent longitudinal bars have oppositely directed bulges formed by a single pressing operation.
This aspect of the invention preferably is further characterised in that the longitudinal bars protrude above the level of the transverse bars, the protruding portions of the longitudinal bars being castellated.

Brief Description of the Drawings

The invention will now be further described, by way of example, with reference to the accompanying drawings in which

Figure 1 is a perspective view of a grating according to the invention;
Figure 2 is an underneath view of the grating shown in Figure 1;
Figure 3 is a side view of the grating shown in Figure 1;
Figure 4 shows a plan view of a plate after a punching operation to form slots across the central axis; and
Figure 5 shows an end view of a transverse bar after punching and folding along the central axis, and a longitudinal bar castellated along its upper edge prior to insertion in a slot in the transverse bar.

Description of a Preferred Embodiment

The section of finished grating shown in Figure 1 is made up of transverse bearer bars 1 and longitudinal bars 2. Each transverse bearer bar has a U-shaped cross-section, as can be most clearly seen in Figures 3 and 5. The U-shape in fact approximates to a V-shape, but in practice there will always be some radius at the apex of the section, and the section is accordingly described as U-shape. Furthermore, it is preferred to have a slightly rounded apex, for it will be appreciated that it could be uncomfortable on the feet of a person walking over the grating if the apices of the transverse bearer bars are too sharply pointed.
It will also be seen in the drawings that the longitudinal bearer bars 2 have castelled upper edges. This serves as an aid in the prevention of slippage on the grating. It will be appreciated that the gratings of the type under consideration are often used at substantial elevations, and that slippage of a person walking over the grating could have disasterous consequences.
The transverse bearer bars 1 are formed in the following manner: Strips of flat plate are passed beneath a punch, which is operated to punch a series of transverse slots 5 from the plates across their central axes. One such plate is illustrated in Figure 4 after the punching operation.
The plates are then folded to the shape shown in Figure 5 about the central axis. The resulting U-section then has a series of spaced slots 5 located along its apex.
The transverse bearer bars 1 are then arranged in a special parallel relationship with the corresponding slots in each bar directed upwardly and in alignment with one another, ready to receive longitudinal bars 2 to form the grating.
The longitudinal bars 2 are lengths of flat bar. The bars 2, prior to their insertion into the slots, are castellated along their upper edges to provide a better foothold for persons using the grating.
Each longitudinal bar 2 is then forced as a tight press-fit at a point 3 into one row of aligned slots. It should be noted that the dimensions of the slots are such that when the plate has been folded to produce the transverse bearer bars, the depth of the slots is not sufficient to receive the full depth of the longitudinal bars. The castellated portion of each longitudinal bar protrudes above the level of the apices of the transverse bars, as can clearly be seen in Figure 3. As the longitudinal bars are forced into the slots in the transverse bars, the tightness of the fit may result in the upper edge of the steel of the transverse bars being subjected to compression, i.e. a "prestressing" of these upper edges takes place. A slight bowing of the transverse bars may even take place. It will be appreciated that this acts to increase the overall strength of the assembled grating. It will be seen that the continuity of material at the level of the apices of the transverse bars in the present invention makes for greater strength in compression along the upper edges of the transverse bars than does the lack of continuity of material in the earlier disclosure.
Once all the longitudinal bars have been forced into their slots, the undersides of these bars are deformed to prevent their withdrawal from the slots. Referring to Figure 2, it will be seen that the longitudinal bars are derformed by causing them to bulge sideways as shown at 4 in Figure 2. In practice, a single pressing head having an operative thickness greater than the spacing of the longitudinal bars is caused to act between the two adjacent longitudinal bars of a pair in the space between the legs of each U-section to cause the bars to bulge in opposite directions. In view of the rapidity and simplicity of the deforming operation, it is desirable to deform the longitudinal bars in the region between the legs of each transverse bearer bar, so as to provide greater rigidity to the whole structure.
It has been found that gratings according to the present invention have a weight some 30% less than comparable gratings which exhibit similar strength. This is mainly due to the method of formation of the transverse bearer bars. It has been found that a suitable thickness of plate for use in preparing the transverse bearer bars is 3 mm for most applications. Such plate is not excessive in weight, and is easily punched and handled.
In practice, it has been found necessary in some applications to fold the legs of the transverse bars into almost parallel alignment with one another. This configuration allows lumps of coal etc. to fall freely between the transverse bars without becoming jammed. It will be appreciated that this would be difficult to achieve if the transverse bearer bars were formed from angle section steel in view of the difficulty in bending the legs of the angle towards one another.
The grating described also allows for a better protective coating to be applied to the finished grating. The fact that no complex crimping operations take place along the apices of the transverse bars, with no resulting sharp edges, allows for greater uniformity of coating of, say zinc, in a galvanising process. The tightness of the fit in the slots also acts to lessen the likelihood of relative movement between the two sets of bars, with less resulting abrasion between bars and destruction of a coating which has been applied.
A further, readily ascertainable advantage of the present invention lies in the punching operation to form the slots in the apices of the transverse bars. It will be appreciated that it is easier to punch slots from a flat plate than it is to punch or cut the slots laterally from the apex of a steel angle section.
Furthermore, the present invention is applicable to gratings intended for almost any span. With steel sections, the designer is limited by the angle sections available. With increasing angle size, there will be increasing fabrication difficulties. Gratings formed according to the present invention can be designed to suit a wide range of spans, by, for example, increasing or decreasing the length of the legs of the transverse bars, as the case may be.

Claims

1. A floor grating which has a plurality of inverted, U-shaped transverse bars (1) and a plurality of rectangular longitudinal bars (2), the longitudinal bars (2) locating in slots (5) formed in the apices of the transverse bars (1) and being deformed in those regions lying within the U-shapes, characterised in that the longitudinal bars (2) are flat bars which are press-fits in the slots (5), in that the transverse bars (1) are formed by folding them from flat plate, in that the longitudinal bars (2) are deformed without cutting into the material of the longitudinal bars (2) so that their depth is substantially the same in those regions lying within the U-shapes as in those regions lying outside the U-shapes, and in that pairs of longitudinal bars (2) have oppositely directed bulges (4) formed by a single pressing operation.

2. A floor grating according to claim 1, characterised in that the longitudinal bars (2) protrude above the level of the transverse bars (1), the protruding portions of the longitudinal bars (2) being castellated.