Abstract:
A decking panel is provided having first and second ends and fasteners at each end for releasably clipping the panel to a pair of support or catenary wires. The fasteners comprise hooks for supporting the panel on the wires and at least one finger for resisting lift of the panel from the wires, wherein the hooks and finger or fingers at one end are offset from the hooks and finger or fingers at the other end. In embodiments a cross-member at each end of the panel pivotally supports a lever carrying the finger or fingers, the lever being rotatable between a vertical position where the fingers are clear of the hooks and a lowered position wherein the fingers underlie the hooks for clamping a catenary cable between them, gravity biasing the levers towards the lowered position. At either end of the panel treadplates may be hinged to the panel at pivot axes spaced from the ends of the panel with free ends at least partially overlying the levers, the treadplates being liftable form a normal lowered position in which the fingers are covered to a vertical position where the levers are user-accessible. The invention also provides a load platform comprising catenary wires and panels as aforesaid clipped to the catenary wires for providing the platform. In an embodiment adjustable support chains are connected to the catenary wires at intervals between their ends for supporting vertical load, and the adjustable support chains are connected to catenary wires by friction clips that surround the catenary wires and frictionally engage therewith to inhibit the catenary wires from being pulled through them in the event of wire failure. In a further embodiment tensioners in the catenary wires are fitted with in-line load cells permitting the tension in the wires to be set to a desired value.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention provides a deck panel supportable on a pair of spaced parallel support (catenary) wires and a platform of a plurality of the catenary wires carrying a multiplicity of the deck panels. It also provides a T-clamp useful e.g. in platforms of the above kind for attaching tension members e.g. slings to the wires. It further provides an in-line tensioning device for catenary cables and its use in platforms supported by catenary cables. 
       BACKGROUND TO THE INVENTION 
       [0002]    U.S. Pat. No. 5,299,655 (Margaritis) discloses suspended structures providing a workplace beneath bridges and other like structures. Cables are each fixedly connected at opposite ends to said underlying bridge supports and lie parallel to one another in a substantially common horizontal plane spaced a predetermined distance below the substructure, tension in the cables being adjustable by means of turnbuckles. The two outermost cables are spaced from one another by a distance at least substantially as great as the width of said bridge. Load-bearing flooring is supported by the cables and extends the full width between the outermost cables and the full length between the bridge supports. The floor is constructed of chain-link fence which is unrolled so as to lay on the cables, and is wrapped around the cables and secured thereto with clips, after which the chain-link fence floor is covered with nylon tarpaulin or other fluid-impermeable material. 
         [0003]    U.S. Pat. No. 5,730,248 (Apostolopoulos) aims to provide an improvement on such platforms by reducing the time needed to erect and dismantle them, and to provide rigid support for workmen standing or walking thereon. Flooring sections or panels of sheet material of elongated rectangular shape corrugated for strength at right angles to the cables together form a platform, are supported by the under-bridge longitudinal cables in side-by-side relationship and are removably connected thereto. Each connection is formed by a plate which engages the upper surface of a panel and a generally U-shaped member which is attached to the plate to extend downwardly therefrom to be received in a panel opening and to receive the cable. The free end of the member is threadedly attached to another plate wherein the two plates generally cover the opening with the cable securely received between the legs of the U-shaped member. U.S. Pat. No. 6,138,793 (Apostolopoulos) provides a connector assembly which has a manually operated lever for selectively placing the connector assembly in clamped or un-clamped positions relative to the cable and flooring section. However, these connector arrangements have been criticised as unduly complex. The first described arrangement it requires two parts to be assembled as well as a nut which must be screwed onto the free end of the member, i.e., a total of three separate parts as well as an electric or other wrench for applying the nut sufficiently tight. The second lever-based arrangement requires two parts to be assembled as well as a pin (or nut and bolt) for added safety. 
         [0004]    A rope clamp having a pair of jaws for clamping about a rope or cable and having an eye for attachment of a second rope is shown in U.S. Pat. No. 0,779,019 (Agobian). The disclosed utility is for uniting ends of ropes. Forming an attachment at an intermediate position along a rope or cable for a second rope, wire, chain or the like in tension in a direction out of alignment with the first rope about which clamping is effected is neither disclosed nor suggested. A clamp having a pair of jaws for fastening about a wire rope and having a hook attached to one of the jaws for attachment of a second wire rope, e.g. a guy rope is disclosed in U.S. Pat. No. 0,928,367 (De Witt). However, it is apparent that load on the hook from the guy rope in a direction out of alignment with the main rope tends to pull the jaws apart rather than tighten them about the rope. By way of background, a further clamp for gripping a cable or rope based on a pair of jaws is shown in U.S. Pat. No. 4,143,446 (Down). The jaws are screw clamped together and can accommodate in-line an accessory permitting attachment of a hook, eye, shackle, swivel or the like. However, it will be apparent from the drawings that the Down attachment only enables this to be achieved at an end of the rope. 
         [0005]    Some embodiments of the invention provide panels which can be fitted easily and rapidly to catenary wires with minimal gaps, or with gaps of predetermined relatively small dimensions, between their ends to form a load platform. 
         [0006]    Other embodiments of the invention provide panels that can be fitted to at least three support wires in rows and columns with at least two adjacent panels having a common support wire, the panels being configured so that they may be fitted either in aligned rows or in a staggered arrangement. 
         [0007]    It is a further object of the invention to provide a platform comprising panels clipped between catenary wires, wherein the effects of failure of a catenary wire are relatively localised, support along the length of the platform being at least partly retained. 
         [0008]    It is a further object of the invention to provide platforms supported by catenary wires in which the cables are optimally adjusted. 
         [0009]    A yet further object of the invention is to provide friction clamps e.g. for use in association with load-carrying members e.g. straps, wires, chains or slings that are of improved structure and properties. 
         [0010]    It will be appreciated that the invention has a number of diverse aspects, and individual embodiments may not achieve ann or indeed any of the above objects. 
       SUMMARY OF THE INVENTION 
       [0011]    In one aspect the invention provides a decking panel having first and second ends and fasteners at each end for releasably clipping the panel to a pair of wires by which it is to be supported, said fasteners comprising hooks for supporting the panel on the wires and catch assemblies each including at least one finger for resisting lift of the panel from the wires, the catch assemblies being covered by treadplates hinged to the panel with free ends facing outwardly and at least partly overlying the hooks, raising the treadplates from the panel providing access to the catch assemblies. Clipping can be achieved without the use of tools, which is an advantage in such areas as an underdeck of jetties, rigs, bridges and pipe racks. The underdeck can provide a solid and stable work platform that feels like scaffolding and users may be able to carry out a variety of heavy work tasks off the deck as if it were scaffolding. 
         [0012]    In a further aspect the invention provides a decking panel having: first and second ends; and fasteners at each end for releasably clipping the panel to a pair of wires by which it is to be supported, said fasteners comprising hooks for supporting the panel on the wires and at least one catch for resisting lift of the panel from the wires; wherein the hooks and a catch or catches at one end are offset from the hooks and a catch or catches at the other end. 
         [0013]    In a further aspect the invention provides a decking panel having: first and second ends and fasteners at each end for releasably clipping the panel to a pair of wires by which it is to be supported; said fasteners comprising hooks for supporting the panel on the wires and catch assemblies at each end of the panel for resisting lift of the panel from the wires, each catch assembly comprising a cross-member pivotally supporting one or more levers each carrying a catch finger, the or each lever being rotatable between a raised position where the finger or fingers are clear of the hooks and a lowered position where the finger or fingers register with the hooks from underneath for clamping a support cable between the hooks and the fingers; and treadplates at each end of the panel, hinged thereto at pivot axes spaced from the ends of the panel and with free ends facing towards the ends of the panel, the treadplates being liftable from a normal lowered position in which the or each catch assembly is concealed by the treadplate to a raised position in which the or each catch assembly is user-accessible. 
         [0014]    For use in an inter-tidal zone there may be provided a decking panel for forming a load platform, said panel having first and second ends and fasteners at each end for releasably clipping the panel to a pair of wires by which it is to be supported, the panel comprising a pair of longitudinal styles, cross-members between the styles and decking in the form of a grating or expanded metal. 
         [0015]    In a further embodiment the invention provides a load platform comprising spaced parallel wires supporting a plurality of panels as defined above. 
         [0016]    In a further aspect the invention provides a T-clamp for fitting to a rope in tension and for attachment of a member which in use is loaded in a direction transversely of the rope, said clamp comprising: first and second elongate members; hinge formations at one end of said members forming parts of a hinge that connects the members together for movement between an open position in which the rope is insertable into and removable from the clamp and a closed position in which the first and second members contact one another and the rope is retained in the clamp; first and second clamping jaws in said members for closing about and frictionally engaging the rope, one side of each clamping jaw being adjacent the hinge; first and second stem regions of each of said members arising from sides of the clamping jaws opposite to the hinge and extending away from the hinge in a direction transversely of the clamping jaw; and first and second hook or eye regions extending from ends of the first and second stem regions opposite to the hinge and together defining an a hook or eye for receiving an eye or hook of the member, load on said first and second eye regions urging the clamp towards its closed position. 
         [0017]    The invention also provides in combination a clamp as aforesaid and a wire or chain sling, the first and second members having eyes and the sling having a hook. 
         [0018]    A load platform according to the invention comprises support wires, decking clipped to the support wires for providing the platform, and one or more slings or straps attached at their upper ends to a structure beneath which the load platform is slung and attached at their lower ends to the wires at one or more intermediate positions along their length, the attachment being by T-clamps as aforesaid and lower ends of the slings being said members, the clamps being configured to frictionally engage the wires for impeding the wires from travelling through them. 
         [0019]    In another embodiment the invention provides a load platform comprising support wires and panels clipped to the support wires for providing the platform, wherein adjustable support chains are connected to the support wires at intervals between their ends for supporting vertical load, and the adjustable support chains are connected to support wires by friction clips that surround the support wires and frictionally engage therewith to inhibit the support wires from being pulled through them in the event of wire failure. 
         [0020]    A further aspect of the invention provides a platform comprising: decking panels each having first and second ends and each comprising (a) fasteners at each end for releasably clipping the panel to a pair of wires by which it is to be supported, said fasteners comprising hooks for supporting the panel on the wires and catch assemblies for resisting lift of the panel from the wires, and (b) treadplates at each end of the panel, hinged thereto at pivot axes spaced from the ends of the panel and with free ends facing towards the ends of the panel, the treadplates being liftable from a normal lowered position in which the or each catch assembly is concealed by a treadplate to a raised position in which the or each catch assembly is user-accessible; at least three spaced parallel wires supporting a plurality of decking panels arranged in at least two columns, adjacent decking panels of different columns having a common support wire; one or more slings or straps attached at their upper ends to a structure beneath which the platform is slung and attached at their lower ends to the support wires at intermediate positions along their length; and clamps providing attachment of the lower ends of the slings or straps or legs thereof to the support wires, the clamps being configured to frictionally engage the wires for impeding the wires from travelling through them, the clamps being located on the support wires within the widths of individual panels and free edges of treadplates of adjacent panels at a common support wire being spaced apart to permit portions of the clamps attached to the support wire to pass upwardly between the treadplates. 
         [0021]    It will be appreciated that in this embodiment by locating the clamps on the support wires within the widths of adjacent panels it is not necessary to space apart decking panels of the rows at the sling or strap positions. In embodiments upper ends of the clamps are formed with eyes for receiving hooks at the lower ends of the slings or straps or legs thereof. In further embodiments the clamps may comprise first and second members hinged together below the support wires, said members having concave clamping regions for fitting about the support wires and stems extending from the clamping regions to above the treadplate, portions of the stems defining eyes that coincide for receiving hooks of the slings or strap or legs thereof. 
         [0022]    A further embodiment of the panel comprises a decking panel having first and second ends and fasteners at each end for releasably clipping the panel to a pair of wires by which it is to be supported, the panel comprising decking and a support framework including a pair of longitudinal styles, wherein the upper regions of the styles have upstanding formations and lower regions of the styles having matching recesses or sockets in which at least uppermost regions of the upstanding formations can be received, whereby when one panel is stacked on another, displacement of the upper panel laterally is resisted. 
         [0023]    Another aspect of the invention provides a load platform comprising support wires and panels clipped to the support wires for providing the platform, wherein the support wires are secured to tensioners configured for sensing tension and setting tension in the wires to a desired value. Although turnbuckle tensioners are known, the applicants have not found a turnbuckle tensioner with a built-in load cell or other tension-measuring device. In applications involving load-carrying generally horizontal wires in tension, as in the present load platforms, it is desirable to be able to set a determined tension in the wires without over-tensioning. 
         [0024]    A yet further embodiment of the invention comprises a tensioner for a support wire, rope or the like comprising a body and oppositely acting screw jacks together extensible from and retractable into the body on rotation thereof, attachments at the ends of the screw jacks for wire eyes or the like, and a measuring device for measuring tension applied to the wire. 
         [0025]    It will be appreciated that the features set out above may be used in combination with one another and in sub-combinations. Thus any of the preferred decking panels, support chain and clamp arrangements, tensioners and load platform arrangements may be used in association with one another and, for example the support chain and clamp arrangements and the tensioners may be used with other types of decking panels. 
         [0026]    Thus the invention further provides a load platform comprising support or catenary wires and panels clipped to the catenary wires for providing the platform, wherein adjustable support chains and clamps are connected to the catenary wires at intervals between their ends for supporting vertical load, and the adjustable support chains are connected to catenary wires by friction clips that surround the catenary wires and frictionally engage therewith to inhibit the catenary wires from being pulled through them in the event of wire failure, the catenary wires being secured to tensioners configured for sensing tension and setting tension in the wires to a desired value. 
       BRIEF DESCRIPTION OF PREFERRED FEATURES 
       [0027]    The above decking panel in embodiments is generally rectangular and comprises a pair of longitudinal styles and cross-members between the styles. The cross-members may include ladder-like cross-members and/or diagonal cross-members defining a truss-type structure. 
         [0028]    Embodiments of the styles are extrusions in aluminium. Such extrusions may in embodiments each comprise a region of box section into which the hooks fit, portions of the region of box section defining outer and inner webs spaced apart transversely of the panel, one hook at each end of the panel being fastened to the outer web of one of the styles and the other hook at each end being fastened to the inner web of the other of the styles. Such extrusions may further comprise portions of the region of box section that define an upper generally horizontal web from which an upstanding wall arises and portions that define a lower generally horizontal web formed with a recess into which at least uppermost regions of the upstanding walls can be received, whereby when one panel is stacked on another lateral displacement of the upper panel is resisted. Each style may be formed adjacent each end at its inner vertical web with fixing formations for attachment of fastening plates of a catch assembly and/or for attachment of hooks, and may be formed adjacent one end at its outer vertical web with fixing formations for attachment of a hook. 
         [0029]    In alternative embodiments the styles are of rolled steel, e.g. in channel, I or Z-section. In this case, the styles may each comprise a portion defining a web to which hooks are attached, one hook at each end of the panel being fastened to the web of one of the styles directly or at a relatively small spacing, and the other hook at each end of the panel being fastened to the web of the other of the styles with a spacing that is larger than the spacing for said one style, the styles and hooks being configured so that the hooks at one end of the panel are offset transversely of the panel relative to the hooks at the other end of the panel. The styles may further comprise portions that define an upper generally horizontally-directed web from which upstanding pins, ribs or other formations arise and portions that define a lower generally horizontally-directed web formed with recesses or sockets into which at least uppermost regions of the upstanding pins, ribs or other formations can be received whereby when one panel is stacked on another lateral displacement of the upper panel is resisted. 
         [0030]    In embodiments of the above panel, the cross-member carries a pair of levers spaced apart transversely of the panel and interconnected at or adjacent their ends facing away from the support cable by a handle. For ease of fitting to support wires in both aligned and staggered arrangements, the pair of levers is conveniently spaced apart by about one third of the width of the panel. Each finger may be formed with a recess defining an upwardly-facing hook for engagement with the underside of the support cable or it may have a plate-like surface engageable with the support wire, friction between the fingers and the support wire inhibiting lateral displacement of the panel. 
         [0031]    Decking may be wooden e.g. of plywood, may be of metal or may be of expanded metal especially where the decking is to be used in tidal conditions and may be submerged at some states of the tide. 
         [0032]    For support at intermediate longitudinal positions the above load or work platform may further comprise one or more slings or straps attached at their upper ends to a structure beneath which the load platform is slung and attached at their lower ends to the support wires at one or more intermediate positions along their length. Lower ends of the slings or straps or legs thereof may be attached to the support wires between adjacent pairs of panels or may be attached to the support wires at locations within the widths of individual panels. In either case, the lower ends of the slings or straps or legs thereof may be attached to the support wires by clamps (e.g. two-part hinged T-clamps) configured to frictionally engage the wires for impeding the wires from travelling through them. Free edges of treadplates of adjacent panels at a support wire may spaced apart for access of the support wire and upwardly-facing portions of clamps attached to the support wire may extend between the treadplates. 
         [0033]    For tensioning the support wires the tensioners may comprise a body and oppositely acting screw jacks together extensible from and retractable into the body on rotation thereof. They may further comprise a ratchet for controlling rotation of the body and a handle for effecting rotation, and their opposed ends may incorporate bifurcated shackles and pins for attachment to wire eyes or the like, the in-line sensor being between one of the screw jacks and a shackle. 
         [0034]    With reference to the above clamp, there may be further comprised apertures in the first and second stem regions adjacent said first and second hook or eye regions for receiving a retaining bolt. In some embodiments the first and second stem regions and the first and second hook or eye regions together define planar surfaces that are in contact in the closed position. To reduce point loads and permit the member to be at an angle relative to the clamp, in some embodiments internal faces of the first and second hook or eye regions at least adjacent ends of the first and second members opposite to the hinge are internally profiled to define a continuous curved surface for receiving an eye or hook of the member. 
         [0035]    In general in relation to load platforms, the decking may comprise panels clipped or otherwise releasably fastened to the wires, in which case embodiments of the panels comprise a pair of longitudinal styles and cross-members between the styles. Lower ends of the slings or straps or legs thereof in some embodiments are attached to the support wires between adjacent pairs of panels and in other embodiments are attached to the support wires within the widths of individual panels. Alternatively in some embodiments the decking comprises tensioned netting clipped to the support wires, e.g. polyester netting. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    How the invention may be put into effect will now be described by way of example only with reference to the accompanying drawings, in which like parts are so far as practical represented by the same reference numerals, and in which: 
           [0037]      FIG. 1  is an isometric view of a short section of a first embodiment of a suspended load platform and associated support or catenary wires with treadplates of deck panels together providing the load platform shown in their raised position to reveal the catenary wires and parts of opening mechanisms of the deck panels; 
           [0038]      FIG. 2  is a plan view of a first embodiment of a deck panel forming part of the load platform of  FIG. 1  and  FIG. 3  is plan of one end of the panel on a larger scale; 
           [0039]      FIG. 4  is a side view of a casting forming part of an opening mechanism for the deck panel of  FIGS. 2 and 3 ; 
           [0040]      FIG. 5  is an end view of the deck panel with its treadplates in their closed flat position; 
           [0041]      FIG. 6  is a partial section of the deck panel on the line A of  FIG. 3  showing part of a style and of the opening mechanism; 
           [0042]      FIG. 7  is a section of a style forming part of the deck panel of  FIG. 2 ; 
           [0043]      FIG. 8  is an oblique view of an end of the load panel with its treadplate raised showing the release mechanism and a short length of support or catenary wire; 
           [0044]      FIG. 9  is a perspective view of a first embodiment of a clamp forming part of a support strap for supporting a catenary wire at an intermediate position along its length; 
           [0045]      FIG. 10  is a plan of a tensioning device useful in tensioning catenary cables of load platforms of the general kind illustrated in  FIG. 1 , the device being in its fully retracted state; 
           [0046]      FIG. 11  is an oblique view of the tensioning device of  FIG. 10  in its fully extended state; 
           [0047]      FIG. 12  is a view on an enlarged scale of an in-line load cell forming part of the tensioning device of  FIGS. 10 and 11 . 
           [0048]      FIG. 13  is a perspective view of a pair of styles forming part of a second embodiment of the deck panel; 
           [0049]      FIG. 14  is a side view of a hook and a lever forming part of the deck panel of  FIG. 12 , said lever incorporating an underhook; 
           [0050]      FIG. 15  is a partly exploded perspective view of one end of a deck panel according to the second embodiment, and  FIG. 16  is an underneath view of said end in in an assembled state; 
           [0051]      FIG. 17  is an underneath perspective view of the panel of  FIG. 12  with one treadplate in a partly raised state and the other treadplate in a lowered state and showing solid decking; 
           [0052]      FIG. 18  is an underneath perspective view of a third embodiment of the panel employing expanded metal decking and  FIG. 19  is an enlarged top perspective view of the panel of  FIG. 18  showing a treadplate and an adjacent region of decking; 
           [0053]      FIG. 20  is an underneath view showing six decking panels in position on support wires; 
           [0054]      FIG. 21  is a view showing five decking panels in position on support wires, with two of the decking panels staggered relative to the other three; 
           [0055]      FIG. 22  is an exploded perspective view of part of a style of a further embodiment of the panel together with a spacer, hook and cross-member fixing plate, the style being in rolled steel; 
           [0056]      FIG. 23  is a side view of portions of adjacent deck panels adjacent a common support wire, styles and hooks being removed to reveal the support wire, overlapping underhooks and a second embodiment of a T-clamp fitted to the support wire; 
           [0057]      FIG. 24  is a front view of the T-clamp shown in  FIG. 23 ; 
           [0058]      FIG. 25  is an enlarged perspective view of part of the support wire, the T-clamp shown in  FIG. 23 , and a hook and part of a chain forming part of a chain sling for supporting a load platform; and 
           [0059]      FIGS. 26 and 27  are perspective views of first and second members together forming a clamp as illustrated in  FIG. 23 , the views showing the inner faces of the members. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0060]      FIG. 1  shows a short section of work platform erected for demonstration purposes. Catenary wires (also referred to herein as support wires)  10   a ,  10   b ,  10   c  are supported under tension in spaced parallel relationship from a fixed structure, in this instance posts  17  and rails  16 , the ends of the catenary wires being attached to the rails  16  by attachment fittings  18   a - 18   c . The catenary wires in an embodiment may be 16 mm diameter wire rope, 6×36 lay with an internal wire rope core, the internal core imparting resistance to stretching. For demonstration purposes in the illustrated embodiment an upper set of catenary wires  12   a ,  12   b ,  12   c  is provided. Adjustable support chains  14  or slings with attachments  15  at each of their ends are provided at intermediate longitudinal positions for supporting the catenary wires  10   a ,  10   b ,  10   c  from an overlying structure, in this instance the catenary wires  12   a ,  12   b ,  12   c . In this embodiment the attachments  15  at each end of the chains take the form of friction clamps e.g. as described below. Deck panels  20   a - 20   l  e.g. of length 2-4 metres (e.g. 2 metres, 3 metres or 4 metres) fit onto and are supported by the catenary wires  10   a - 10   c  in abutting relationship side-to-side and end to end in a column and row arrangement as shown. UK working at height regulations require that the deck should have a minimum of gaps or spaces through which tools or other items could be inadvertently dropped, and similar requirements exist in other countries. Further, there is a risk of lateral displacement of the panels e.g. during the course of erection of the platform and it is desirable to provide means for increasing the resistance of the load platform to such displacement. 
         [0061]    The arrangement of  FIG. 1  is only diagrammatic, and the support for the load platform will vary widely depending on the structure to which the load platform is fitted and the task to be performed. The structure may be e.g. a steel bridge, a concrete bridge, a jetty, a marine platform or any other large structure where an underneath temporary work platform needs to be provided e.g. for inspection or maintenance purposes. In many instances the overlying structure may incorporate or be fitted with eyes which provide convenient attachment points for an under-slung work platform. For example in the case of a concrete bridge structure, eye-bolts can be fitted to the sides and underside of the bridge. Slings may be fastened between the eyes and the load platform catenary wires and may e.g. be single leg or two leg slings e.g. in chain or wire rope. An oblong master link at the upper end of each sling may be connected to a respective eye by a hook, e.g. a latched or locking hook, or by a shackle or by other fastening means. The or each sling leg may have a hook at its lower end that fits under and supports the catenary wire, but preferably is fitted at its lower end with a friction clamp that surrounds and frictionally engages the catenary wire to both provide local support for that wire and resist it sliding through the clamp as described below. In the case of a jetty having one or more large steel pipelines passing along it, adjustable support chains may be passed over the pipelines from one side to another and the ends of the adjustable support chains may act as the adjustable support chains  14  of  FIG. 1  carrying clamps  15 . The number of catenary wires and of rows of deck panels will depend on the size of the structure that it is needed to inspect or maintain and in some embodiments the platform will extend the whole length and width of the overlying structure or it may extend over or along a region of that structure where inspection or repairs are to be carried out. 
         [0062]    As is apparent from  FIG. 2 , the deck panels  20  may conveniently take the form of ladder-type structures with styles  22 ,  24  and cross-members or rungs  26 . Such structures are more convenient and may carry greater loads than corrugated metal sheet panels. 
         [0063]    Styles  24  which are conveniently aluminium extrusions are shown in enlarged section in  FIG. 7  and are of box-section with at their upper outer edges upstanding stepped walls  60  and at their lower outer edges matching recesses  62 . Panels can be stacked one on top of another for storage or transport with the upper step regions of the walls  60  fitting into the recesses  62  to avoid lateral displacement of one panel relative to another and to hold the upper panels at a predetermined spacing just above the lower panels. In the embodiment shown the height of the box-section is 50 mm and its width is 35 mm, its side webs are 2 mm thick and its top and bottom walls are 4 mm thick. The wall  60  has a total height of 12 mm or 15 mm, a width at its base of 6 mm and a width at its stepped top region of 3 mm. The relatively thick base region of the wall  60  and the top wall of the box portion together define a step into which wooden decking or metal sheet or mesh can fit and be retained. The 3 mm thick top region of the wall  60  fits into the recess  62  of an overlying style which is 3 mm wide and 3 mm high. The dimensions given above can be varied without departing from the invention, but are intended to provide a general teaching as to preferred dimensions and proportions for some, but not all, embodiments of the invention. The cross-members or rungs  26  may be square, oval or any convenient section and are attached to the styles to form a rigid structure. Further, parallel ladder-type cross-members as illustrated are only one possible form of construction and other forms of framework e.g. planar truss frameworks e.g. with a single diagonal pair of cross-braces, two or more pairs of cross-braces or Allan or Howe-type truss configurations could equally be used, the over-riding requirement being for a lightweight open framework with sufficient strength for the intended load and giving sufficient support for the intended decking. 
         [0064]    Decking  40  is laid on the ladder-type or other framework structures and is attached thereto, the decking being of timber, metal sheet or metal mesh or grating, aluminium or steel being preferred. Where the platform is of mesh or grating, it may conveniently be used to erect a platform in tidal conditions where it will be covered with water at some states of the tide. In the present embodiment the decking may be of plywood. 
         [0065]    Opposed ends of the deck panels are formed with hooks  28   a ,  28   b ,  30   a ,  30   b  attached to the styles  22 ,  24  for fitting opposed ends of the deck panels onto respective pairs of catenary wires  10   a ,  10   b  or  10   b ,  10   c  as shown in  FIG. 1 . As can be seen in  FIG. 3 , hooks  30   a ,  30   b  are attached asymmetrically to styles  22 ,  24  within the box section of each style. Hook  30   a  is attached to the outer vertical web of style  22  and hook  30   b  is attached to the inner vertical web of style  24 , the corresponding hooks at the opposite end of the panel having the reverse fixing arrangement. The hooks have a thickness in this embodiment of 6 mm and resist bending. The staggered arrangement of the hooks at each end when a pair of panels  20   a ,  20   g  has adjacent ends supported by a common catenary wire  10   b  allows the panels to be in alignment without interference between the adjacent hooks of the two panels. 
         [0066]    Each deck panel is provided at each end with a catch sub-assembly or operating mechanism  32 ,  34  for retaining the panel in position on its catenary wires against lifting or other displacement forces e.g. from wind or in the case of a load platform that may be submerged at some states of the tide from estuarine or tidal currents. The catch sub-assemblies are normally covered by hinged treadplates  52  which normally lie flat but which can be rotated upwards to give access to the underlying catch sub-assembly  32  or  34 . Retaining fingers  36   a ,  36   b ,  38   a ,  38   b  are movable into contact with the catenary wires from below to prevent the deck panels being inadvertently lifted off the catenary wires e.g. in high winds. Again as seen in  FIGS. 3 and 5  the fingers  38   a ,  38   b  are laterally offset in one direction and the corresponding fingers at the opposite end are laterally offset in the opposite direction so that fingers of adjacent panels do not clash when a pair of panels  20   a ,  20   g  has adjacent ends supported by a common catenary wire  10   b.    
         [0067]    As apparent from  FIG. 3  a catch sub-assembly for an end of a treadplate comprises a tubular cross-member  54  which provides a pivot axis for a pair of operating levers  42   a ,  42   b  and generically indicated as  42  in  FIG. 4 . Each operating lever which can be made as a casting comprises a base  46 , an upstanding web  48  formed with apertures into which handle  44  fits, an aperture  50  for forming a bearing with cross-member  54  which fits into that aperture, and a finger or under-hook generically indicated as  38  which projects forwardly and is movable into and from engagement with the underside of catenary cable  10  as shown in  FIG. 8 . The fingers  38  in this embodiment are bar-shaped and have width greater than their depth, this aspect ratio being selected so that they present relatively wide friction surfaces to the catenary cable. The width of the fingers in an embodiment may be about 35 mm. When the deck panel is in position on a pair of cables, gravity maintains the fingers  38   a ,  38   b  in engagement with the undersides of the cables and the weight of the base  46  and web  48  acting about the pivot provided by cross-member  54  urges the fingers upwardly. The resulting frictional force at each end of the panel provides resistance to the panel becoming displaced laterally on the cables e.g. because of slight slope the cable as when workers are standing on the platform created by the deck panels or heavy objects are placed on it, or as previously mentioned by wind and/or tide. An advantage of the present mechanism is that it can operate purely by gravity, no additional clip or fastening mechanism being needed, although the use of such additional mechanisms is not excluded if additional reassurance is required. As is apparent from  FIG. 5 , the cross-member  54  is located a short spacing inboard of the ends of the styles  52 ,  54  and at a vertical position below the top of the styles. Compared to a front-hinged treadplate carrying locking fingers, the pivot axis can be moved further away from the wire. The position of the cross-members longitudinally and vertically relative to the ends of the styles can be adjusted for specific tasks so that e.g. if a deck panel is required to clip onto something other than a cable e.g. a support of steel angle, then only minor adjustment of the position of the cross-member  54  is needed. 
         [0068]    A first cross-member  64  extends between styles  22 ,  24  immediately behind the operating levers  42  and carries hinges  66 . A second side of the hinges attaches to a second cross-member  68  of angle section fitted to the treadplate  52 . Thereby the treadplate  52  is hinged to the panel for rotation about an axis spaced inboard and slightly above the pivot axis for the release mechanism provided by cross-member  54 . As previously explained, it will normally lie flat as shown supported by the horizontal top walls of the styles  22 ,  24  as in  FIG. 5  (where a slight gap is shown for clarity) or by support pads on the upper surfaces of the styles but can be lifted by raising its forwardly-facing free edge as in  FIG. 8 . In the illustrated embodiment the cross-member  54  is located 40 mm inboard of the ends of the styles  22 ,  25 , whereas the treadplate hinge is located about 201 mm inboard. It will be noted that the ends of the operating levers  42  are located almost immediately underneath the inner hinged ends of treadplate  52 . If the panel is subject to lift e.g. by wind the fingers  38   a ,  38   b  will tend to be rotated away from register with the brackets  30   a ,  30   b , tending to release catenary wire  10 . As most clearly apparent in  FIG. 6  the levers  42  then contact the treadplates  52 , but are unlikely to lift the treadplates  52 . The reason is that the line through the points of contact of the levers  42  with the treadplate  52  is close to the axes of hinges  66  and although upward load may be applied to treadplate, that load exerts little rotational power on the treadplate. Magnetic catches (not shown) adjacent the free end of the treadplate provide additional resistance to unintended lifting of the treadplate and since the catches can be spaced along the styles  22 ,  24  from the axis of hinge  66  they can offer significant resistance to inadvertent rotation. The free edge of the treadplate extends beyond the styles  22 ,  24  and overlaps the hooks  30   a ,  30   b , almost overlying the centre of the hooks with the shortfall in this embodiment being about 3 mm. Accordingly when two panels are assembled end-to-end on a common cable, the gap between the support surfaces that they provide can be as little as 6 mm and the treadplates almost meet one another with no downwardly curved region between them where articles can lodge. However, the position of the free edges of the treadplates is arbitrary and a wider gap can be adopted e.g to permit the stem of a T-clamp on the wire rope to pass upwardly between them as described below. 
         [0069]    Laying a deck panel on its catenary wires is a two-person operation. A person at each end of the panel lifts the treadplates  52  to a vertical position, grips handle  44  and lifts that handle to a vertical position, rotating the fingers  38   a ,  38   b  clear of hooks  40   a ,  40   b . The handles  44  are then conveniently positioned for carrying the panel. At the start of laying, the panel is positioned over the catenary wires e.g.  10   a ,  10   b  and lowered into place. Release of the handles  44  permits the opening mechanisms to rotate by gravity until the fingers  36  engage the catenary wire, after which a small force on the treadplates  52  allows them to fall under gravity into their fully lowered position. The mechanism is therefore robust and simple to operate, and it is resistant to inactivation as a result of paint or other materials which are likely to become deposited on it during service and which in other designs of deck panel jam the release mechanism and may prevent operation. 
         [0070]      FIG. 8  shows the treadplates  52  partially raised to reveal the release mechanism. Spacer tubes  70   a ,  70   b  on cross-member  54  between the styles  22 ,  24  and the operating levers  42   a ,  42   b  define asymmetric locations for the levers and fingers  38   a ,  38   b . In this way the fingers of adjacent deck panels at ends facing one another on the same catenary wire do not interfere. 
         [0071]      FIG. 9  shows a generally T-shaped strap clamp  15  used in particular to fasten a strap  14  to a catenary wire  10   a , the strap providing support to the catenary wire at a position partway along its length. Up to now attachment between the adjustable support chains and the catenary wire has been via hooks as are conventional for rope or chain slings, but although these provide lift they offer no resistance to pulling the catenary wire through them. There is no reason to expect a catenary wire to break or be cut through, but provision for very rare events with serious consequences is desirable. Strap clamps  15  are formed in halves  80 ,  81  pivoted together at  82  and together define a cavity  84  which surrounds and frictionally engages the catenary wire. Through holes  86  receive a captive bolt and integral threaded fitting to receive the threaded end of the bolt. (not shown) to hold the parts firmly together about the wire and exert a frictional load on the wire preventing it being pulled through the clamp even if the wire should break or be cut. The upper end  88  of the clamp in this embodiment is bifurcated to receive an eye of a support wire or chain which can be attached to the clamp by a pin inserted into through-holes  90 . In consequence, should the catenary wire be cut or break, vertical support is maintained and the damage to the load platform is localised. In this embodiment owing to the close spacing between treadplates of adjacent decking panels the strap clamps  15  are fitted to the support wires between adjacent deck panels and fitting within the width of a deck panel is not possible. As apparent in  FIG. 1 , therefore, small gaps are present between adjacent panels  20   c ,  20   d ,  20   i ,  20   j  to permit stems of the strap clamps to pass upwardly above the level of the deck panels and provide attachment for wire or chain slings or the like. 
         [0072]    Deck panels in aluminium according to the embodiments described above may be lightweight e.g. about 14 kg/m 2  and may for example have a loading capacity of 0.5 kN to 5.5 kN UDL/m 2  depending upon the requirements of a particular job. They are easily maneuverable and easy to rig, and installation time may be reduced compared to scaffolding. 
         [0073]    The combination of catenary wires, support straps and clamps is also useful where polyester tension netting is provided between catenary wires in place of the panels described in the previous Figures. 
         [0074]    It has been found that the catenary wires of load platforms of the present kind give optimum performance and stability when the catenary wires that provide support are tensioned at or adjacent a best value which will, of course, vary depending on the particular structure under which the load platform is to be slung, and that excessively high or low tensions are better avoided. For that purpose the catenary wires may incorporate in-line load cells of the kind illustrated in  FIGS. 10-12 . Thus such a tensioning device may have body  100  fitted with oppositely acting jack screws  102 ,  104  shown fully retracted in  FIG. 10  and fully extended in  FIG. 11 . A reversible ratchet mechanism  116  and handle  118  enables body  100  to be rotated in either direction, so as to extend or retract the screw jacks and hence increase or decrease the tension of a catenary wire into which the tensioner is incorporated In an embodiment the handle and ratchet mechanism enable a person to develop approximately 50 N (50 kg) force to wind the tensioner in or out. The pre-tension on the catenary wire is important as if the tension is too high it is necessary to reduce the load capacity of the decks. So in some embodiments applicants pretension between 5 and 10 kN, using the handle. The screw jacks terminate at a first end fitting  106  and a second end fitting  108  each connected to a shackle  112 ,  114  for receiving an eye of a catenary cable or the like which is securable in place by pin  120 ,  122 . The pins are inserted into holes in the shackle and are held in place by smaller retaining pins  126 . 
         [0075]    Between the end of jack screw  104  and shackle  114  the end fitting  108  is an in-line load cell incorporating a pre-calibrated spring-operated load measuring arrangement providing an output by movement of indicator member  128  through a calibrated window, the member indicating by its position the load which e.g. may be between 0 and 30 kN. It will be appreciated that other types of load cell may be employed, e.g. based on strain gauges and electronic devices including a display, but a simple spring-loaded device may be more convenient especially where the platform is to be in place for extended periods and is subject to adverse weather. However a transducer could be incorporated to provide an overload indicator alarm. 
         [0076]      FIG. 13  is perspective and partly inverted view of styles  22 ,  24  forming part of a load platform according to a second embodiment of the invention, the styles being aluminium extrusions having the same cross-section as in  FIG. 7  and provided with hooks  28   a ,  28   b  at one end and hooks  30   a ,  30   b  at the other end. Each style is formed with a region defining a box section formed in an inner face or web  212  adjacent the ends thereof with patterns of fixing holes  218 ,  218   a , in this case four, for attachment of a catch sub-assembly and/or for attachment of hooks  28   a ,  28   b ;  30   a ,  30   b . Apertures  218  also adjacent the ends and coinciding with the patterns of fixing holes correspond to tubular cross-members  54 . The region of box section also has an outer face or web  210  formed adjacent one end with fixing holes  214  for a hook  28   a ,  28   b ;  30   a ,  30   b . With this arrangement the hooks may be fitted to the outer or inner webs or faces of the box section as appropriate, using fixing holes in the same spatial arrangement, and fixing plates for the catch sub-assemblies may use the same spatial arrangement of fixing holes on the inner webs  212 . However on each style only a single hook can be attached to the outer face or web. The inner webs  212  are also formed adjacent their ends with fixing holes  222 ,  222   a  for hinge plate pivots and fixing holes  220 ,  220   a  for decking cross-members. 
         [0077]      FIG. 14  shows a hook plate  28  and a lever  36   a ′ forming part of a catch sub-assembly  32  or  34 . The hook plate has a downwardly-facing hook region  224  having at its forward end a linear lead-in region  232  leading to a quarter-round upper forward region  234 , an upper linear central region  236  which in the case of 16 mm wire rope may be about 5 cm in length (i.e. about a third of the diameter of the rope) and leading to a curved rear region  238 . With this hook profile, the panel may be fitted onto a support wire  10   a ,  10   b  or  10   c  with a certain amount of misalignment or twisting being accommodated without damage to the rope. The hook plate is formed with a pattern of fixing holes  230  corresponding to those in the styles and also at its lower edge with a recess bounded by faces  226  and  228  to permit the plate to slide into the hollow box region of a style without interference from recess  62 . Catch lever or underhook  36   a ′ is formed with aperture  244  so that it can fit rotatably onto cross-member  54  and adjacent its rear or inner end with fixing hole  246  for attachment of handle  44 . It has an outwardly or forwardly facing finger  240  formed at its upper edge with an arcuate recess  242  for receiving a support wire, the centre of the hook and the centre of the recess  242  coinciding at line  248 . 
         [0078]    In  FIG. 15  which is a view of an end of a deck panel in partly exploded view, there appears one of the two decking cross-members  250  which is of inwardly-facing angle-section so as to underlie and support the ends of decking  40  with side plates of said cross-members fastened to the styles  22 ,  24  at fixing holes  220 . Treadplate  52  has attached to its rear end on the underside thereof an attachment member  252  also of angle-section formed with side plates  254   a ,  254   b  with through holes for hinged attachment at fixing holes  22  of the styles, the position of the hinge axis for each treadplate being defined by the location of the fixing holes  222 . Also appearing in  FIG. 15  is catch sub-assembly  32  comprising cross-member  54  which has forwardly and rearward-facing curved regions and upper and lower planar regions that non-rotatably fit into apertures  278  ( FIG. 22 ) of mounting plates  256   a ,  256   b . The levers or underhooks  36   a ″,  36   b ″ fit rotatably onto the cross-member  54  and are positioned transversely of the cross-member by friction collars  36   a ″. As may be seen, their spacing is about one third of the width of a deck panel to facilitate positioning of adjacent panels on different support wires both in alignment and in staggered relationship as described below. Handle  44  is connected between the levers or underhooks adjacent inner ends thereof. The mounting plates  256   a ,  256   b  are each formed with fixing holes  258  disposed in a pattern corresponding to those in the styles.  FIG. 16  shows an end of the deck panel with both the treadplate  52  and the catch sub-assembly  32  attached between the styles. The underside of a deck panel with one of its treadplates raised appears in  FIG. 17 , the decking  40  being of plywood or other sheet material.  FIG. 18  is an underneath view of another embodiment of the decking panel with decking  260  of expanded aluminium mesh or honeycomb or aluminium grating. Since this form of decking is more flexible than plywood, a longitudinal stiffening bar  262  is fitted. In the above deck panels, catches may be provided, e.g. magnetic catches, for holding the treadplates in their lowered position when installed as part of a load platform in a work area against inadvertent lifting through the action of wind or water currents e.g. in an intertidal zone. 
         [0079]      FIG. 19  is an underneath view of panels  20   a - 20   c  of one column and  20   g - 20   i  of an adjacent column, the panels being in alignment and alignment being facilitated by the offset relationship in the hooks and the catch sub-assemblies  32 ,  34 .  FIG. 21  is an underneath view on an enlarged scale showing ends of panels  20   a - 20   c  of one column and panels  20   h ,  20   i  of another column, this staggered relationship within rows being facilitated by the relatively close spacing of the underhooks of the catch sub-assemblies  32  and  34 . 
         [0080]    Although aluminium is a preferred material, generally square sections in steel may be rolled for some markets where steel is more practical and the rolled sections may have complementary protuberances and recesses on their upper and lower faces which interfit to allow stable stacking as described above although the precise shapes for aluminium cannot be duplicated in rolled steel and rolled steel styles will differ from those shown Rolled steel sections may be of any conventional shape provided that a vertical web portion is provided, and they may, for example be of channel, I or Z-section, channel section being convenient in some embodiments. Further sections are C- or channel section with their flanges formed at their ends with return (in-turned) regions or flanges which in some embodiments can significantly increase strength and stiffness. In  FIG. 22  a style  274  of channel section is formed adjacent its ends with a pattern of fixing holes  276  corresponding to the pattern of fixing holes  230  in hook member  28 . A spacer block  270  is provided and has fixing holes  272  in a pattern corresponding to that in the style  274 . Also shown is fixing plate  256   a  of a catch sub-assembly. It will be appreciated that a spacer block  270  may be provided at each end of the resulting decking panel in the style  274  on one side but not the other, and in this way the hooks  28  may be attached in a similar staggered arrangement to those in the previously described embodiments. As regards stacking the panels, the styles may further comprise portions that define an upper web from which upstanding pins, ribs or other formations arise and portions that define a lower web formed with recesses or sockets into which at least uppermost regions of the upstanding pins, ribs or other formations can be received whereby when one panel is stacked on another lateral displacement of the upper panel is resisted, these pins, ribs, etc. are not shown but can easily be implemented. 
         [0081]    In  FIGS. 23-25  there is shown end regions of a pair of adjacent load platforms having a common support wire  10   b  to which the load platforms are clipped inter alia by brackets  28   a ,  30   b  and underhooks  36   a ′ and  36   b ′. Above support wire  10   b  the free ends of treadplates  52  are spaced apart to define a gap of e.g. about 25 mm. The wire  10   b  carries a T-clamp generally indicated by the reference numeral  280  having a clamping region that fits tightly around and friction grips the wire  10   b  and a stem that arises from the support wire and passes between the support plates so that its upper regions are accessible above the support plates. The T-clamp comprises clamping members  282 ,  284  interfitting at their base with a pair of spaced barrel hinge formations  310 ,  312  on the first member  282  between which fits barrel hinge formation  314  on the second member  284 , the hinge being completed by hinge pin  286 . Above the barrel hinge the members  282 ,  284  are formed with generally semi-cylindrical clamping regions  281 ,  283  which fit around and grip the cable  10   b , their axes being parallel to and spaced from the hinge axis. Inner faces of the clamping regions  281 ,  283  are formed with inclined gripping teeth  315  matching the lay of the wire rope  10   b , the inner diameter of the clamping regions being slightly smaller than the wire rope, e.g. 15.75 mm for a wire rope of diameter 16 mm so that they can firmly grip the rope but not crush it. Each member  282 ,  284  has a stem region  316 ,  318  arising from the clamping region, the stem region having a width greater than its depth and the two stem regions together having a depth of e.g. about 17 mm so that the stem can pass between the plates  52 . Adjacent the upper end of the stem region the member  284  is formed with a socketed through-hole  288  for receiving the head and threaded region of clamping bolt  301  and member  282  is formed with a corresponding threaded through-hole  290  for receiving the threaded region of bolt  301  to permit the halves of the clamp to be fastened firmly together about the support wire. Each of the clamping members  282 ,  284  is formed at its head with a formation defining an eye region  294 ,  296 , the eye regions together defining eye  292 . As can be seen in  FIGS. 23 ,  26  and  27  the inner faces of the stems  316 ,  218  are planar and continue without change of attitude into planar faces of eye regions  294 ,  296  so that in the closed position the two members  282  and  285  touch one another as apparent in  FIG. 23 . It will be appreciated that other profiles are possible provided that the two members can close and touch one another, but the illustrated profile is convenient and easy to manufacture. The inner profiles of eye-regions  294 ,  296  are generally quarter-round or otherwise form a generally continuous smooth curve as best seen in  FIG. 23  so that when engaged by a clamping hook, rope other member to be tensioned, load on the member to be tensioned is transferred equally to both eye regions and the load can be applied in directions up to 45° in any direction whilst applying pulling force but not unacceptable twisting force to the clamp. Without a smooth curved surface of this kind, there would be an increased risk of a hook of a sling or the line applying point loads which would limit the rated tensional load that the T-clamp can accept. The members  282 ,  284  are conveniently drop forgings in alloy steel e.g. Grade 100 alloy steel and may be zinc passivized so that they can withstand harsh external environments. 
         [0082]    A hook  302 , e.g. a safety hook, of a chain sling is insertable into the eye  292  and provides a lower connection for the chain sling. The eye region  292  is generally oval or otherwise has extended height to allow the T-clamp to sit generally vertically on support wire  10   b , and the hook  302  is configured to be rotatable in any direction at an angle of up to about 45° to the vertical, thereby permitting the loading on the individual eye-regions  294 ,  296  of the clamping members to be equlised. It will be appreciated that if a T-clamp as shown here is fitted about a support wire  10   b , hook  302  is engaged therewith and the cable  304  is tensioned, then the clamp will be held tightly about the wire irrespective of whether bolt  301  has been inserted and a substantial clamping force is exerted by simple tension applied to the eye regions  294 ,  296 , so that at least a temporary fixing to the wire  10   b  can be made with a minimum of labour. The retaining bolt and the sockets  288 - 290  are configured so that for an intended support cable the clamp cannot be over-tightened, and one of the major purposes of bolt  301  is to prevent a clamp once fitted to support wire  10   b  from being inadvertently dropped before attachment of a hook or other tensioning device. 
         [0083]    It will be appreciated that various modifications may be made to the embodiment described herein without departing from the invention, the scope of which is defined by the accompanying claims.