WO1997008040A1

WO1997008040A1 - Extendible flatbed trailers

Info

Publication number: WO1997008040A1
Application number: PCT/GB1996/002053
Authority: WO
Inventors: Kevin William Raven; Paul Anthony Raven
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-08-26
Filing date: 1996-08-23
Publication date: 1997-03-06
Anticipated expiration: 1998-02-26
Also published as: AU6827196A

Abstract

The present invention relates to extendible flatbed trailers which may be connected to and towed by a truck, and in particular to extendible flatbed trailers having a substantially flat floor when extended. An extendible flatbed trailer (1) comprises a chassis section (2), and a wheeled bogie section (3) slidably connected to the chassis section and relatively movable between extended and retracted positions. The chassis section supports a first floor (4), which has a number of transversely hinged panels (39), and the bogie section supports a second floor (5), the first and second floors presenting an elongate load bearing surface which is hingedly extendible as the sections are moved from a retracted to an extended position. There is essentially no step in the load bearing surface between the first floor (4) and the second floor (5) when the sections are in an extended position.

Description

Extendible Flatbed Trailers

The present invention relates to extendible flatbed trailers which may be connected to and towed by a truck, and in particular to extendible flatbed trailers having a substantially flat floor when extended.

There are many variety of flatbed trailers which may be connected to and towed by a truck. Some consist mainly of a floored surface above the trailer frame,- others have additional structural elements, for example, fold-down sides, curtain sides or top, rigid sides or top, and vertical side pillars. Such trailers are often used to transport a wide variety of items such as palletised goods, concrete or steel beams and logs.

The front of a trailer, or alternatively the rear of a truck, may be provided with a hydraulic crane for loading and unloading the trailer, normally to and from the side of the trailer. The arm of the crane should ideally be able to reach to the back of the trailer, although there is normally a trade-off between the capacity of the crane and the reach of the arm. The cost of a crane increases rapidly with the required reach. For example, a 13 m crane may cost five times as much as a 6.5 m crane, which may amount to several times the cost of the trailer alone.

Flatbed trailers can also be adapted to carry 6.1 , 12.2 m or 13.7 m (20, 40 or 45 foot) containers by the provision of flip-up standard twist-lock container mounts in the flatbed floor. However, in practice, it may not be possible to carry a single heavily loaded 6.1 m container. This is because neither the front nor the rear half of the flatbed trailer will provide a suitable mounting location. For such a heavy short container, the problem with using the front half is that the weight of the container will not be over the trailer wheels, and the problem with using the rear half is that the load on the trailer is too distant from the truck.

Because a flatbed trailer may at times need to be only partially loaded, it may be desirable for the flatbed trailer to be extendible. One example of an extendible flatbed trailer is described in EP 0 551 159 Al which discloses a trailer with curtain sides and top with a flatbed floor in two box-frame sections. The floor sections are centrally supported on an extendible chassis, with the forwards floor section sliding over the rearwards floor section as the trailer is retracted. Whilst this arrangement provides a flat floor surface when the trailer is retracted, there is a substantial step between the floor section surfaces in the extended position. This may be inconvenient if a load such as a pallet has to span such a step. The step may also make it more difficult to use a fork lift truck on the flatbed, and the step may potentially become damaged if struck by the fork lif truck tines. Such a step may also present a tripping hazard to workers on the flatbed surface.

It is an object of the present invention to provide an extendible flatbed trailer with a reduced step or with no step between floor sections.

Accordingly, the invention provides an extendible flatbed trailer comprising a chassis section, a wheeled bogie section slidably connected to the chassis section and relatively movable between extended and retracted positions, the chassis section supporting a first floor and the bogie section supporting a second floor, the first and second floors presenting an elongate load bearing surface which is hingedly extendible as the sections are moved from a retracted to an extended position, there being essentially no step in the load bearing surface between the first floor and the second floor when the sections are in an extended position.

The term "essentially no step" as used herein means either no step, or a small step which is shallow enough to avoid a tripping hazard, or to allow the loading of a palletised load across the step, or to avoid a hazard with fork lift truck tines. ^' It has been found in most cases that this means a step of less than 20 mm height. A somewhat larger step, for example up to 50 mm, may be tolerated if the step has an oblique taper or ramp between the floor surfaces.

The floors may have a number of panels, each panel being transversely connected to an adjacent panel and being adapted to lay flat and comprise a part of the load bearing surface when the sections are in an extended position. The panel may be connected to just one adjacent panel or, if the panel is bounded by two adjacent panels, to both adjacent panels.

In a first embodiment, the panels will most generally be rectangular or square panels, with seams between adjacent panels lying transverse to the length of the trailer and the direction of movement in extension or retraction. The connection between panels may be a hinge, which is preferably recessed from the floor surface so as to protect the hinge from wear and tear as the flatbed trailer is loaded and unloaded.

The panels may then be adapted to concertina as the sections are moved to a retracted position. The concertina action will generally be a folding action above the level of the support surface as the trailer is retracted, with adjacent sections folding vertically parallel as the trailer reaches the retracted position. The folding action may be driven by the retraction of the underlying chassis or bogie section, with the ends of the endmost concertina'd panels being fixed. The concertina'd panels may then collapse flat under their own weight as the trailer is extended.

The number of concertina sections may be between two and about ten sections. The advantage of using a larger number of sections is that the height of the concertina above the level of the support surface is reduced.

It may be desirable, for the sake of safety, to include a side guard, and preferably a side guard at each side of the trailer, along the length of one of the floors in order to conceal the concertina'd panels as they fold up or collapse flat. This would prevent any potential entrapment or injury due to the motion of the panels.

In a second embodiment of the invention, the panels are adapted to roll up at one end of the supporting surface as the sections are moved to a retracted position. The panels may therefore have a narrow rectangular shape so that the panels may be rolled up into a cylinder, which may be above or below the level of the floor. Alternatively, the panels may roll underneath the floor. A larger number of panels may facilitate a tighter bend radius as the panels are rolled up.

In this embodiment, a container, for example a cylindrical container, may be provided at one end of the supporting surface to receive the rolled up panels. The panels may be guided at side edges into the container by a track.

In a third embodiment of the invention, each floor is composed of a set of parallel fingers, each set of fingers extending along the length of a load bearing surface and being slidably interleaved with the other set of fingers when the sections are moved from an extended to a retracted position. There may be of the order of ten such fingers in each set. In one variant of this embodiment, the fingers in a set may be about as wide as gaps between fingers. Increasing the number of fingers will then reduce the span of any such gap between fingers. The width of a typical flatbed trailer may be up to 2.55 m, in which case with a total of, say, 20 fingers, a gap may be about 128 mm wide, with each finger having a similar width. Such a floor will present a load bearing surface which may be walked over and which may readily be used to support goods such as pallets.

Preferably, the fingers of one set are retained between adjacent fingers of the other set. This retention may be by means of an interlocking feature, such as a tongue-in- groove, between adjacent fingers of each set. The fingers may then slide in an interlocking engagement with each other.

In general, rollers may be provided between each set of fingers.

In another variant of the third embodiment, in which there is a particular type of interlocking slidable engagement between the sets of fingers, each finger is an I-beam. The I-beams of one set can then be placed close to one another so that the gaps between the tops of the first set of I-beams is just wide enough to receive the stem of the second set of I-beams. The I-beams may be of steel or extruded aluminium.

In a further variant, either the top or the bottom of the I-beams may be joined together to form a structure referred to herein as "joined T-beams". If both floors are of this construction, then one section will have downwardly projecting joined T-beams which are slidably interlocked with upwardly projecting joined T-beams. One floor section will then have a continuous surface, with the other floor sections having narrow slots for the stems of the other joined T-beams.

In yet another variant of this embodiment, one floor section may have joined T-beams with downwardly projecting stems, and the other floor section may have a substantially flat surface with channels therein, the channels being arranged to receive the downwardly projecting stems of the T-beams. The stems may than slide along the channels as the sections are extended or retracted. In this variant, to minimise friction at least one section may have below its floor a set of rollers which are connected to that section and which run on a load carrying track on the other section. These rollers may, for example, be solid steel wheels.

In a fourth embodiment of the invention, a panel slides over an adjacent panel when the sections are moved from an extended to a retracted position to stack the panel over the adjacent panel. The panels therefore lie flat when the trailer is extended and are pushed one on top of another as the trailer is retracted. Preferably, just one panel stacks on top of another, in which case the length of the retracted section is halved. Whilst this embodiment of the extendible trailer may not therefore be extendible or retractable over as great a distance as the other embodiments described above, the stacked sections may be arranged to present a flat surface which may be used to carry a load. There will, of course, be a step between this retracted flat surface and the surface of the other trailer section.

In order to facilitate the stacking of one panel atop another, a pair of adjacent panels may have an oblique seam therebetween, with one of the panels riding up over the oblique seam as the panel is stacked over the other panel.

The extendible flatbed trailer may have additional structural elements above the floor of a section for containing a load. For example, the trailer may have any of: fold-down sides, curtain sides or top, rigid sides or top, and vertical side pillars.

The trailer may also be used for containerised transport, particularly for standard 6.1 m or 12.2 m containers, if the trailer has suitable mounts in the floor of a section.

According to another aspect of the invention, there is provided a truck with an extendible flatbed trailer as herein described, comprising a crane mounted on the truck with an arm for loading and unloading the extendible flatbed trailer.

According to a further aspect of the invention, a crane may be mounted on one of the sections and have an arm for loading and unloading the trailer. This crane is most commonly provided at the front of the trailer. Because the trailer may retract to shorten its length, a smaller crane may then be used to load the rear section of the trailer prior to extending the trailer to load the front section.

In some cases it may be advantageous to locate the crane at the rear of the trailer, since in this location the crane will be able to reach further from the trailer and the truck.

In any case, it is preferable to keep the size and hence the cost and weight of the crane to a minimum, so that the arm of the crane has a reach which is sufficient to load or unload the section of the trailer which is farthest from the crane when the trailer is extended, only when the trailer is in the retracted position.

Also according to the invention, there is provided a method of loading an extendible flatbed trailer attached to a truck, the truck or the trailer having a crane mounted thereon, and the trailer having a floored chassis section, a floored and wheeled bogie section slidably connected to the chassis section and relatively movable between extended and retracted positions, at which positions the sections may be secured into engagement with each other, there being essentially no step between the chassis section floor and the bogie section floor when the sections are in an extended position, the method comprising the steps of: moving the sections to a retracted position,- using the crane to load a first section; moving the sections to an extended position so that the first section moves away from the crane,- and using the crane to load a second section closer to the crane than the first section.

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

Figure 1 is a side view of the extendible flatbed trailer according to the first embodiment of the invention, showing a bogie section and a chassis section in an extended position,-

Figure 2 is a top view of the extendible flatbed trailer of Figure 1, showing a number of rectangular panels covering the chassis section;

Figure 3 is a view of the extendible flatbed trailer of Figure 1 , showing the chassis section being retracted and the rectangular panels being concertina' d into a retracted orientation,-

Figure 4 is a view of the extendible flatbed trailer of Figure 1, showing the chassis section fully retracted;

Figure 5 is a cross-section view of the extendible flatbed trailer of Figures 1 and 2, taken through the line V-V; Figure 6 is a side view of the extendible flatbed trailer of Figure 4, showing the trailer attached to the truck cab having a crane for loading and unloading the trailer;

Figure 7 is side view of the extendible flatbed trailer according to the first embodiment of the invention, showing the trailer in an extended position and with a crane unit fitted to the front of the trailer;

Figure 8 is a side view of the extendible flatbed trailer of Figure 8, showing the trailer in a retracted position;

Figure 9 is a side view of the extendible flatbed trailer according to the second embodiment of the invention, showing a bogie section and a chassis section in a retracted position,-

Figure 10 is a side view of the extendible flatbed trailer according to the third embodiment of the invention, showing a bogie section and a chassis section in an extended position,-

Figure 11 is a cross-section view of the extendible flatbed trailer of Figure 10, taken through the line XI-XI;

Figure 12 is a side view of the extendible flatbed trailer according to the fourth embodiment of the invention, showing a bogie section and a chassis section in an extended position,- and

Figure 13 is a side view of the extendible flatbed trailer of Figure 12, showing the trailer in a retracted position. Referring first to Figures 1 and 2, a first embodiment of an extendible flatbed trailer l has a forwards chassis section 2, and a rearwards bogie section 3, each of which has a floor 4,5 with a load bearing surface. The chassis section 2 has a standard mounting king pin 6 for a fifth-wheel connection to a truck (not shown) , and drop-down front support legs 7 shown in the dropped position.

The rear bogie section 3 has three axles 8 with six wheels 9. The trailer could have fewer sets of wheels, but for larger types of trailers it is preferable to have three axles in order to provide a greater potential load bearing capacity. For the sake of clarity in the drawings, the details of the axle suspension and connection to the rear bogie section 3 are not shown.

The rear half of the extendible trailer 3 has two fifth- wheel type automatic latching mechanisms 10,11 mounted beneath the rear floor 5 on the longitudinal centre line of the trailer. The front half of the trailer 2 has a fixed pin 12 which is vertically aligned and which engages with and automatically latches within either of the latching mechanisms 10,11 when the trailer has been extended or retracted into position. Since the trailer is shown fully extended, the pin 12 is shown engaged within the front latch 10.

The trailer 1 is suitable for carrying palletised loads and other solid or packaged goods which may be strapped down to the floors 4,5 of the flatbed sections. The trailer also has mounting points 13-16 for 6.1 m or 12.2 m containers

(not shown) . These mounts are standard twist-lock mounts, which rotate to pop up above the level of the floors 4,5 so that there is some small clearance between the container and the floor.

Both the front and rear sections 2,3 have a pair of parallel longitudinal chassis members 17,18 made from steel beams. As can be seen from Figure 5, each chassis member 17,18 is formed from parallel steel beams spaced equidistantly from a longitudinal centre line of the trailer. The front chassis member 17 is essentially an I-beam, and the rear chassis member 18 is essentially a C-beam. The C-beams are held together by transverse struts, one of which 32 is visible in Figure 5.

The front chassis members 17 have a set of upper steel rollers 37, and the rear chassis members have a set of lower steel rollers 38. The operation of the rollers can be^' appreciated from Figure 5. The lower rollers 38 roll on a flat bottom surface 41 of the I-beam 18 and the upper rollers 37 roll on a flat lip 42 of the C-beam.

As the sections 2,3 are moved between extended and retracted positions, the rollers 37,38 will roll along the lengths of the beams. The fifth-wheel type automatic latching mechanisms 10,11 stop the sections from moving beyond the extended and retracted positions, when the pin 12 enters the latch and is captured and secured in place by a bolt 43 which is thrust across the pin 12. Each automatic latching mechanism 10,11 may be unlocked by means of an air driven line (not shown) which pulls back the bolt 43 to release the pin 12.

Figures 3 and 4 illustrate how the extendible flatbed trailer 1 may be retracted to shorten its length. The front floor 4 comprises a set of six rectangular panels 39, each of which is hinged to adjacent panels by hinges 40. The hinges are provided upward facing and downward facing alternately along the upper and lower edges of adjacent panels, so that the panels 39 may fold together in a concertina fashion. The end panels are hinged to narrow rectangular fixed panels 66,67, into which are fitted two pairs 13,14 of the pop-up container mounting points . Underneath three panels near the three upward facing hinges are three air diaphragms 45. With a truck cab joined to the trailer, these may be remotely activated via air lines (not shown) and when inflated push upwards underneath the above panel to flex the upward facing hinge. With the trailer wheels 9 braked, the truck cab may then back down on the trailer, as indicated by arrows labelled with numerals 54 and 55.

With three pairs of panels upwardly flexed, this motion will cause the panels to fold together or concertina, until the trailer is engaged in the retracted position. The end-most pair of panels are some what narrower than the intervening panels so that the intervening panels may rest vertically on the front I-beam 17.

Returning to Figures 1 and 2, the load of each section is borne ultimately by the axles 8 or king pin mount 6. When the extendible flatbed trailer 1 is in the retracted position, the load on the rear bogie section 3 will be transmitted directly through the C-beams 18 to the suspension system and axles 8. Since in this position the I-beams 17 are retracted within the C-beams 18, the weight of the front chassis section 2 will be transmitted through the upper set of rollers 37 onto the flat lips 42 of the C-beams, and thence to the axles 8.

When the extendible flatbed trailer 1 is in the extended position, however, both the front and rear sections 2,3 may carry a load, and there will in general be a twisting moment about a horizontal axis perpendicular to the length of the trailer, which would tend to pull the sections apart towards the rear end of the front chassis section 2. In order to prevent this from happening, the rollers 37,38 are more closely spaced towards the rear of the chassis section 2 and front of the bogie section 3. In use, the steel rollers 37,38 would be lubricated with oil so that the sections could be retracted and extended smoothly.

Spaced transverse ribs are provided to brace the beams 17,18, and are indicated in the drawings by numerals 51 to 53. Struts may also provide reinforcement between the beams and the sections; one such pair of struts 56 may be seen in Figure 11, discussed in more detail below.

The extendible flatbed trailer 1 described above is 12.2 (40 feet) long when in the extended position, and 7.92 m (26 feet) long when retracted. The width of the trailer may be up to 2.55 m.

Figure 6 shows the extendible flatbed trailer 1 connected to a truck cab 61. The cab has a rearwardly disposed crane unit 62 which may be used to load and unload the extendible flatbed trailer 1 in the following manner. With the trailer empty and extended, the trailer wheels 9 are braked and the forward fifth-wheel type automatic latching mechanism 10 is released remotely. The truck 61 then reverses to retract the trailer 1 until the rear automatic latching mechanism 11 engages with the pin 12 to secure the trailer in the retracted position.

The crane 62 may then be used to load the flatbed trailer, for example with pallets of bricks 63, generally from the side, although a longer crane could load from the rear, until the load bearing floor 5 of the rear bogie section 3 has been loaded.

With the trailer wheels 9 still braked, the rear automatic latching mechanism ll is remotely released and the truck driven forwards until the trailer is secured in the fully extended position. The crane 62 may then load the front chassis section 2. The above described operation is the same when the crane 62 is incorporated with an extendible flatbed trailer 71, as illustrated in Figures 7 and 8. In these illustrations, the approximate location and size of the crane 62 when folded is shown schematically by a box outline. The construction and operation of this trailer 71 is similar to that of the previously described trailer 1, except that when the trailer is fully retracted, the front chassis section 72 does not retract fully towards the rear bogie section 73, so that a shelf 75 remains extended to support the crane unit 62. The shelf 75 is provided by the elimination of two of the six panels 39.

Figure 9 shows a second embodiment of an extendible flatbed trailer 91, which has a set of twenty-four narrow rectangular panels 99 which are fixedly hinged to each other and which are hinged at the end-most panels: at one end to a panel 97 fixed to the front I-beam 17,- and at the other end to a roller 98. The roller is held within a generally cylindrical enclosure 96. This enclosure would have closed ends, but has been illustrated for clarity with open ends so that the operation of the enclosure can be more easily seen.

The enclosure 96 is fixed to a forward end of a front chassis section 92, and the panels 99 retreat within the enclosure when the trailer 91 is retracted. To improve the packing of the panels 99 within the enclosure 96, the panels become progressively narrower from the fixed panel 97 to the roller 98.

The front and rear sections described in detail above may readily be made with floor levels that are level along the join between the front and rear sections to within 3 mm when the trailer is in the extended position. In practical terms, this is "no step".

A third embodiment of the invention is illustrated in Figures 10 and 11. An extendible flatbed trailer 101 differs from the embodiments described above in that forwards and rearwards floor sections 104,105 are in the form of strips or fingers 106,107. The rear floor 105 has four fingers 107 in the form of T-beams each welded along their length to adjacent T-beams. The forward floor 104 has five fingers^' 106 with four channels 108 therein which receive downwardly projecting stems 109 of the T's.

The channels and stems act to stiffen the floor sections so that the floor sections may carry peak loads of up to about 5000 kg/m² and a total load of up to 23,000 kg, without undue bowing.

The forwards floor 104 slides underneath the rearwards floor 105 when the sections are retracted. The two floor sections 104,105 are therefore not exactly coplanar, but are separated in level by about 25 mm. A small ramp section 110 is therefore provided at the forward edge of the rear floor section over a distance of about 100 mm to ease the transition between the floor levels.

The fingers 106 of the forwards floor 104 are all joined to a transverse beam 111 at the front of the forwards section 102. The outside pair of these fingers are each provided with sets of rollers 112 which roll on a shelf 113 which extends laterally from the rear C-beam 18. The shelf is braced at points by lateral struts 56.

The inner three of the forwards fingers 106 are folded underneath around the T-stems 109 and have two sets of rollers 114 which roll on the flat tops of the C-beams 18.

A fourth embodiment of the invention is shown in Figures 12 and 13, in which an extendible flatbed trailer 121 has a rearwards bogie section 122 similar to that of Figure 1, apart from a rear automatic latch mechanism ll set further forwards. A forwards chassis section 123 has a floor 124 with three floor panels 126,127,128, the end pair of which are fixed to the chassis section I-beam 17.

A tapered seam 138,139 is provided between the inner panel 127 and each adjacent panel 126,128, so that when the trailer is retracted, the inner panel rides up over each of the adjacent panels, as indicated by the arrows 130. Two pairs of hinge straps 131 are provided, one pair on each side, between the inner panel 127 and each of the pair of adjacent panels 126,128. The four hinge straps 131 are each pivotally attached to points on the inner panel 127, and slidably engaged with channels 132,133 which extend along sides of the outer panels 126,128. The inner panel is therefore retained with the adjacent panels as it rides up over these panels when the trailer is retracted.

Whilst this embodiment of the extendible flatbed trailer 121 is not retractable and extendible to the same extent as the embodiments described above, the retracted section still provides a useful flat load bearing surface 140 which may be loaded with goods.

The various panels described above in the chassis floor may be formed from light-weight materials such as wood or from aluminium alloy sheets.

Because all of the embodiments described above have hinges between panels in the front floor to allow the front floor to fold in on itself and so shorten the front floor, the embodiments of the present invention all avoid the need, as in the prior art document EP 0 551 159 Al, for one floor to retract underneath the other floor. This allows the chassis slider design to be simpler, because there is no need to accommodate the front floor under the rear floor in the retracted position. The extendible flatbed trailer may be provided with additional structural elements above the floor of the sections. For example, the rear half of the trailer may have drop-down sides, which would allow the trailer to haul a load which could not be fully secured by means of straps alone. The front half of the trailer could then be used for more securely packaged goods, for example pallets.

There are a wide number of other potential uses, where the flexible nature of the extendible trailer could be used to advantage. For example, the trailer could be adapted for road repair work, with the rear half of the trailer having a tip-up container, and the front half being used to transport equipment such as a road roller.

In one variant not shown in the drawings, the rear floored section, may be made to be removable, for example by having the rear floor removably attached at points by bolts to the C-beam. The rear floor could then be removed in order to reduce weight and increase the permissible payload of a container.

The extendible flatbed trailer could be fitted with curtain sides or top, or even with solid sides with a foldable top. In the latter example, the rear half of the sides could slot into a cavity in hollow-walled front sides when the trailer was retracted.

A particular advantage of the present invention is that it permits full sized trailers to be loaded and unloaded with the use of a smaller and much more economical crane unit. Because there is a trade-off between the reach of the crane arm and lifting capacity, it will also be possible to use a cheaper crane and still achieve greater lifting capacity.

The lack of any substantial step between the front and rear floor sections also means that the full extent of the extended floor may be loaded. Fork lift trucks and workers may traverse the extended floor without the risk that a foot or tine may catch with a step, thus avoiding a potential safety hazard.

The ability to alter the length of the trailer could also provide other economies. For example, when travelling by ferry, the trailer could be retracted when not fully loaded and so reduce the length-related charges for the ferry crossing.

Claims

1. An extendible flatbed trailer comprising a chassis section, a wheeled bogie section slidably connected to the chassis section and relatively movable between extended and retracted positions, the chassis section supporting a first floor and the bogie section supporting a second floor, the first and second floors presenting a elongate load bearing surface which is hingedly extendible as the sections are moved from a retracted to an extended position, there being essentially no step in the load bearing surface between the first floor and the second floor when the sections are in an extended position.

2. An extendible flatbed trailer as claimed in Claim 1, in which one of the floors has a number of panels, each panel being transversely connected to an adjacent panel and being adapted to lay flat and comprise a part of the load bearing surface when the sections are in an extended position.

3. An extendible flatbed trailer as claimed in Claim 2, in which the panels are adapted to concertina as the sections are moved to a retracted position.

4. An extendible flatbed trailer as claimed in Claim 3, in which a side guard is provided along the length of one of the floors to conceal the concertina'd panels.

5. An extendible flatbed trailer as claimed in Claim 2, in which the panels are adapted to roll up at one end of the supporting surface as the sections are moved to a retracted position.

6. An extendible flatbed trailer as claimed in Claim 5, in which the panels are adapted to roll up above the floor.

7. An extendible flatbed trailer as claimed in Claim 5, in which a container is provided at one end of the supporting surface to receive the rolled up panels.

8. An extendible flatbed trailer as claimed in Claim 1, in which each floor is composed of a set of parallel fingers, each set of fingers extending along the length of a load bearing surface and being slidably interleaved with the other set of fingers when the sections are moved from an extended to a retracted position.

9. An extendible flatbed trailer as claimed in Claim 8, in which fingers of one set of fingers are retained between adjacent fingers of the other set.

10. An extendible flatbed trailer as claimed in Claim 8 or Claim 9, in which each finger is an I-beam.

11. An extendible flatbed trailer as claimed in Claim 8 or 9, in which one set of fingers are joined T-beams.

12. An extendible flatbed trailer as claimed in any one of Claims 8 to 11, in which rollers are provided between each set of fingers.

13. An extendible flatbed trailer as claimed in Claim 1, in which a panel slides over an adjacent panel when the sections are moved from an extended to a retracted position to stack the panel over the adjacent panel.

14. An extendible flatbed trailer as claimed in Claim 13, in which a pair of adjacent panels have an oblique seam therebetween, one of the panels riding up over the oblique seam as the panel is stacked over the other panel.

15. An extendible flatbed trailer as claimed in any preceding claim, in which the trailer has additional structural elements above the floor of a section for containing a load.

16. An extendible flatbed trailer as claimed in any preceding claim, in which the trailer has mounts in the floor of a section for containerised transport.

17. An extendible flatbed trailer as claimed in any preceding claim, in which the sections have longitudinal chassis members extending below respective floors.

18. An extendible flatbed trailer as claimed in Claim 17, in which a first chassis member from one section is slidably retained within a second chassis member from another section.

19. An extendible flatbed trailer as claimed in Claim 18, in which the first chassis member is an I-beam and the second chassis member is a C-beam.

20. An extendible flatbed trailer as claimed in Claim 19, in which a first set of rollers is retained on the C-beam and a second set of rollers is retained on the I-beam, each set of rollers on each beam running along a support surface on the other beam.

21. An extendible flatbed trailer as claimed in any preceding claim, in which the trailer has a crane mounted on one of the sections with an arm for loading and unloading the trailer.

22. An extendible flatbed trailer as claimed in Claim 21, in which the arm of the crane has a reach which is sufficient to load or unload the bogie section only when the trailer is in the retracted position.

23. A truck with an extendible flatbed trailer comprising a crane mounted on the truck with an arm for loading and unloading the trailer, wherein the trailer is as claimed in any of claims 1 to 20.

24. A truck as claimed in Claim 23, in which the arm of the crane has a reach which is sufficient to load or unload the section of the trailer farthest from the crane only when the trailer is in the retracted position.

25. A method of loading an extendible flatbed trailer attached to a truck, the truck or the trailer having a crane mounted thereon, and the trailer having a floored chassis section, a floored and wheeled bogie section slidably connected to the chassis section and relatively movable between extended and retracted positions, at which positions the sections may be secured into engagement with each other, there being essentially no step between the chassis section floor and the bogie section floor when the sections are in an extended position, the method comprising the steps of: moving the sections to a retracted position,- using the crane to load a first section,- moving the sections to an extended position so that the first section moves away from the crane,- and using the crane to load a second section closer to the crane than the first section.

26. An extendible flatbed trailer substantially as described herein with reference to and as shown in the accompanying drawings.

27. A truck with an extendible flatbed trailer substantially as described herein with reference to and as shown in the accompanying drawings.

28. A method of loading an extendible flatbed trailer attached to a truck substantially as described herein with reference to and as shown in the accompanying drawings.