GB2055211A - Testing load carrying members - Google Patents

Abstract

A method for testing the strength of load carrying members, especially two pallets, in which the two load carrying members are placed opposite each other with their load carrying faces 3 inwards, and restrained from outward movement by securing steel or webbing banding 14 between their opposed ends. An outward pressure is then applied to the inward carrying faces 3, preferably by a hydraulic jack 11 or inflatable bag through two parallel, spaced apart bearers 4 in contact with the inward face of a load carrying member 3 and an H-shaped pressure frame 10 that rests transversely on the two bearers and is acted upon by the hydraulic jack 11. Normally a steadily increasing outward pressure is applied until a required maximum pressure is obtained which is then maintained for a defined time interval. <IMAGE>

Description

SPECIFICATION Improvements in or relating to testing load carrying members This invention relates to a method for testing the strength of load carrying members and to an apparatus for performing the same. In particular the invention relates to a method and apparatus for testing the strength of load carrying pallets, especially "winged" pallets having lateral extensions ("wings") for lifting with slings.

British Standard 2629 Pt. 3 defines a method for testing pallets wherein two parallel bearers are placed in a spaced-apart arrangement on the pallet top deck and a prescribed load is then placed evenly across the two bearers. The under surface of the top deck is supported on two horizontal support arms placed as far apart as possible (in the case of "winged" pallets this is under the wings) and kept aloft for the prescribed period.

Similar tests requiring wire rope or webbing slings are prescribed by other authorities.

Generally the prescribed load which is placed across the two bearers is made up from any readily available heavy objects, for example, railway track, boxes of nails, concrete blocks etc, and these objects are loaded onto the pallet either manually, a process which requires the time and effort of a number of workers, or mechanically, by for example, a fork lift truck. In order to lift the whole assembly further suitable mechanical means, for example an overhead gantry crane or a mobile crane, are required.

If the pallet passes this lifting test the load must be transferred, either manually or mechanically, to the next test pallet. However if the pallet fails the test, and since this is a proving test, the load being above the normal working limits of said pallet, such failures are to be expected, this could lead to the pallet breaking apart thereby shedding the load or violently releasing pieces of timber or metal. Therefore the safety risks associated with this method are evident.

Further disadvantages of the present method of testing are, a) If the load comprises long items these may bear directly on the pallet as it deforms. This means that a true test of the pallet strength, which would require the whole proving load to be placed on the bearers, is not obtained.

b) Although the test pallet is loaded with a standard proving weight, the haphazard methods of loading variously shaped objects onto the pallet means that the present method is not truly standardised.

c) If a manufacturer produces pallets on different sites in his factory, he must, in order to test a sample from each batch, either have suitable equipment, i.e. cranes, trucks, etc., at each site, or he must move samples from each site to a central testing area.

Therefore there are many problems associated with the present method of pallet testing, and indeed similar difficulties are also encountered when determining the load carrying capacity of other load carrying members. Thus there is a need for a method which will minimise the problems of cost, mobility, safety and standardisation. The aim of the present invention is to provide such a method, with which a truly standard test of the strength of load carrying members can be carried out simply and safely, with little expenditure of time or money.

Accordingly the present invention provides a method for testing the strength of load carrying members which comprises, placing two similar members in an opposed relationship with their load carrying faces inwards, restraining the outward movement of the members by securing means simulating the support given to said load carrying members when in normal use, and applying an outward pressure to the inward load carrying faces to simulate loading in normal use.

In practice the pressure is steadily increased until a required maximum pressure is obtained and thereafter said pressure is maintained for a defined time interval.

The pressure may be applied onto said two inward faces by any suitable means known to those skilled in the art. In a preferred embodiment of the invention said pressure is applied by means of a jack, preferably a hydraulic jack, positioned centrally between the two opposed load carrying members. Hydraulic pressure is preferred since this can readily be applied to the piston from a position remote from the test area, by a suitable pump means, and can be readily monitored by simple mechanical means. A further advantage of using hydraulic pressure is that, should there be a sudden structural failure of the load carrying member, this will be immediately preceded by a fall off in the indicated pressure, and hence some warning will be obtained.Moreover, by applying the pressure gradually, seriously defective members will fail below the full pressure and hence with less catastrophic results than if the pressure is suddenly applied by lifting.

In general a slight fall in pressure will be experienced after the test pressure is reached due to leakages and/or deformation of the pallet.

Where the test period is short this may be compensated by periodic checking and repumping. For long test periods, however, it may be necessary to provide an automatic pressure sensor controlling a mechanical pump or else to pressurise the jack from a constant pressure source such as a reservoir acted on by a deadweight piston, or a pressurised gas reservoir.

The pressure should be applied to the load carrying member in a standardised manner.

Although the jack may bear directly on the face of the load carrying member', the pressure is preferably transferred via suitable pressure transferring means, for example comprising at least two parallel, spaced-apart bearers, preferably timber bearers, that are in contact with the inward face of a load-carrying member, and a pressure frame, that rests on the at least two bearers and is acted upon by the applied outward pressure.

Suitable pressure frames are manufactured from materials capable of withstanding the pressures to be applied, for example steel. They may have, for example, square or X-shaped cross-sections, but it has now been found that a pressure frame with a H-shaped cross section is particularly efficient at applying a uniform pressure to the said bearers.

The H-shaped pressure frame may be in longitudinal arrangement with the at least two parallel bearers or, which is preferred, in transverse arrangement with said bearers. In order to place the bearers in substantially the same position on a series of substantially identical load carrying members, suitable locating template means can be employed. Suitable securing means, for restraining outward movement of the load carrying members include rigid frames. However, steel or webbing banding straps, which often support load carrying members in normal use, have been found to act as particularly efficient securing means. During a strength test according to this invention the securing means encircles the whole test rig and thereby constrains the opposed load carrying members against outward movement.For example, when testing winged pallets a strap is passed round the two wings on each side of the pair of pallets.

The invention further provides an apparatus for testing the strength of carrying members comprising a jack, preferably a hydraulic jack, loading distributing members, at least four bearers and at least two banding straps suitable for carrying out the process of the invention. The apparatus preferably also includes templates to assist the relative positioning of the other items.

A particular advantage of this invention is that, unless one of the load carrying members fails the proving test, two load carrying members can be tested simultaneously, leading to a considerable saving of time. Further, the time and manpower required to assemble the test rig of this invention are both considerably reduced compared to the methods of the prior art. Still further, this test can be performed without the assistance of a fork-lift truck, to load the load carrying member, or a crane, to lift said member once loaded. Indeed the equipment required to perform the test is small enough to be moved easily (in for example a car boot) from one site to. another.

Yet another advantage of this invention is that it provides a test of load carrying members that lends itself towards standardisation. For example, it would be very easy to regulate the position and size of the bearers, pressure frame and banding straps.

Although this method is particularly suited for testing the strengthnof pallets, most particularly winged pallets, it is by no means limited to this use. The strength of other load carrying members, for example paving stones, could also be tested readily by the method of this invention.

The method and apparatus of this invention will now be described by way of example only, with particular reference to the figures in which, Figure 1 is a front elevation of an embodiment of the assembled test rig of this invention, comprising two test "winged" pallets and the apparatus of this invention; and Figure 2 is a sectioned view (through A-A') of the embodiment of Figure 1. In each case the pallets are shown in simplified form in the interests of clarity.

In Figure 1, a lower 1 and upper 2 winged pallet are opposed, with their load carrying faces, 3 facing inwards. Two parallel timber bearers 4 lie on the load carrying face of each pallet. The bearers 4 are spaced apart and lie over fork entry spaces 5 between three parallel rows of support blocks 6. For standardisation purposes a hinged wooden template unit 7 comprising a backboard 8, which abuts the side of the pallet, and two side boards 9, extending at right angles from the back board 8, can be used to define the location of the timber bearers 4 and a pair of H-frames 10.

In transverse arrangement with the two pairs of bearers 4 are positioned the H-shaped pressure frames 10. The hydraulic jack 11 lies in central position on the cross-arm 12 of the lower pressure frame whilst the piston 13 of said jack 11 rests against a central position of the cross arm of the upper pressure frame.

The lower 1 and upper 2 pallets are restrained from moving outwards by webbing banding straps 14 that pass round the two opposed left hand wings 1 5 and the two opposed right hand wings 16.

The hydraulic pressure is applied to the piston l3ofthejack jack11.

When hydraulic pressure is applied to the piston 13 of the jack 11, said piston 13 extends out of said jack 11 and thereby applies outward pressure to the pressure frames 10. These frames bear in turn against the parallel bearers 4 which in turn apply outward pressure to the opposed pallets 1, 2. The hydraulic pressure is applied to the piston 13 by means of a hand pump 17, set away from the test rig, and connected to the jack 11 by means of a connecting pipe 18. A measure of the pressure applied to the piston 13 is given by the pressure gauge 1 9.

When the strength of the opposed pallets 1, 2 is to be tested, pressure is applied to them through the jack 11 until the proving pressure is registered on the gauge 1 9. The pressure applied to the pallets 1, 2 is then kept at this maximum value for the desired period. If the test period is short, a slight fall in pressure (registered on the gauge 19) may be compensated by periodic checking and repumping of the hand pump 1 7. If the test period is long the pump 1 7 may be replaced by, either an automatic pressure sensor controlling a mechanical pump or a constant pressure source, such as a large surface area reservoir acted on by a dead-weight piston, to obtain a constant applied pressure.

In an alternative embodiment the webbing band straps 14 pass round the two opposed left hand and right hand fork entry spaces 5. In this embodiment pressure is applied by the jack 11 through H frames onto timber bearers positioned adjacent to the opposed left hand 1 5 and right hand 16 wings of the pallets 1 and 2. In this way the strength test simulates the lifting of the pallets by a fork lift truck.

In a further alternative embodiment the hand pump 1 7 is replaced by an air driven pump connected to an airline through a regulating valve.

In use the vale is opened thereby allowing the air pump to operate the hydraulic jack 11 up to a desired test load, as registered on the gauge 1 9.

Since the air pump compensates for any falling off in the load applied to the pallets 1 and 2 this embodiment may be operated unattended for long test periods.

By attaching the air pump to a series of hydraulic jacks each through a non-return valve this embodiment may be adapted to undertake a series of tests simultaneously.

In a still further alternative embodiment the hydraulic jack 11 is replaced by an inflatable bag.

The inflatable bag applies pressure to the pallets by means of either air or fluid fed into said bag.

This embodiment further reduces the bulk of the test apparatus.

Claims (14)

1. A method for testing the strength of load carrying members which comprises placing two similar load carrying members in an opposed relationship with their load carrying faces inwards, restraining the outward movement of the members by securing means simulating the support given to said load carrying members when 'in normal use, and applying an outward pressure to the inward load carrying faces to simulate loading in normal use.

2. A method according to Claim 1 wherein the outward pressure applied to the inward load carrying faces is steadily increased until a required maximum pressure is obtained and thereafter said pressure is maintained for a defined time interval.

3. A method according to either Claim 1 or Claim 2 wherein the outward pressure is applied to the inward load carrying faces by means of a jack.

4. A method according to Claim 3 wherein the jack is a hydraulic jack.

5. A method according to any preceding Claim wherein the outward pressure is applied to the inward load carrying faces through a pressure transferring means.

6. A method according to Claim 5 wherein the pressure transferring means comprises at least two parallel, spaced-apart bearers that are in contact with the inward face of a load carrying member, and a pressure frame that rests on the at least two bearers and is acted upon by the applied outward pressure.

7. A method according to Claim 6 wherein the pressure frame has an H-shaped cross section.

8. A method according to Claim 7 wherein the H-shaped pressure frame is in transverse arrangement with the at least two parallel bearers.

9. A method according to any of Claims 6 to 8 wherein the at least two parallel bearers are placed in position on the inward face of a load carrying member by a locating template means.

10. A method according to any preceding Claim wherein the securing means comprises steel or webbing banding straps.

11. A method for testing the strength of load carrying members substantially as hereinbefore described with particular reference to the Figures.

12. An apparatus for testing the strength of load carrying members by the method of any preceding Claim which comprises a jack, at least four bearers, at least two pressure frames and at least two steel or webbing banding straps.

13. An apparatus according to Claim 1 2 which additionally comprises a locating template means for positioning the bearers on the inward faces of the load carrying members.

14. An apparatus for testing the strength of load carrying members substantially as hereinbefore described with particular reference to the Figures.