GB2306189A - Falsework - Google Patents

Abstract

A concrete deck spanning two primary support girders may be formed on a temporary platform (24) that comprises removable engagement and suspension members (27) each resting on the upper face of a girder (14). The engagement and suspension members (27) each have means (37) by which transverse supports (25) may be suspended. Upon the transverse supports (25) are located secondary beams (26) that support the decking panels (24). The engagement and suspension members (27) may include releasable securing means (35) to aid in gripping the face of the girder. They may also be provided with a release layer (47) to assist in removal after casting of the deck. The release layer (47) may remain after the removal of the engagement and suspension members (27) to protect the girder flange (14) against moisture and corrosion. An access walkway (not shown) may be suspended from the transverse supports (25).

Description

FALSEWORK The present invention relates generally to falsework and particularly to a falsework support for framework to support a deck, namely a temporary support defining a platform on which a deck composed of castable material may be laid prior to curing and hardening. After the cast material has hardened and become self supporting the falsework and the framework is removed to leave the finished structure in place.

Prior art falsework, because of its temporary nature, is usually formed from a plurality of individual elements which can be fitted together by clamps or screws to form the temporary structure.

In the building of bridges, particularly large bridges for roadways, the main load-bearing members are generally made from steel sections, such as I-beams or girders and H-beams or columns welded or bolted together to form the basic shape of the bridge, and the roadway itself is formed by casting concrete to form a deck or platform spanning two longitudinally-extending main girders which constitute the main bridge supports spanning adjacent columns or piers.

Bridge decks are, of course, internally reinforced by structural steel reinforcement elements which span transversely across the gap between the two main I-beam girders to provide a suitable combination of strength and resistance to bending or flexing without being too heavy.

It is known that concrete, whilst being extremely strong in compression is relatively less strong in shear and although adequate strength could be achieved simply by increasing the thickness of the cast concrete mass to provide several levels of redundancy, the weight of such a massive cast deck would be unacceptably high and would seriously compromise the structural integrity of the bridge and the load-bearing capability of the girders and columns.

Even when an appropriate balance between weight and strength is struck, the mass of concrete involved and its corresponding weight are, nevertheless, very considerable and require to be supported for some time, of the order of several days if not weeks, before being fully cured and sufficiently strong to be self supporting to allow the temporary support to be removed.

In forming such composite decks for bridges and the like it is known to provide a temporary platform in the interspace between the facing upper flanges of the I-beam girders constituting the main bridge supports by a subjacent structure of subsidiary lightweight beams carrying a plywood or like panel the upper surface of which is flush with the upper surface of the I-beam girder flanges to provide a substantially continuous upwardly facing "floor" onto which the concrete is then cast (after having fitted the reinforcing steel work) and allowed to cure and harden.

Because it has been considered necessary to locate the supporting framework platform flush with the upper surface of the I-beam girder flanges the subjacent falsework structure has been built up to be supported on the lower flanges of the I-beams as a lattice of transverse and longitudinal underlying beams. The transverse beams are located in place by clamping devices at each end which allow a clamping pad or foot to be pressed against the web of each I-beam, at opposite ends of the supporting cross beam and extended longitudinally of the cross beam to press against the I-beam flange.

This cross beam is reinforced by inclined legs extending from a point intermediate the length of the cross beam to the lower flange of the I-beam girders, and each inclined leg is provided with length-adjusting means so that its lower foot can be introduced closely into the corner at the junction between the lower flange and the web. In addition, some of the cross beam-inclined leg structures are provided with additional tie rods joining the lower ends of the legs to resist spreading.Nevertheless, the net effect of the lateral forces which are applied to the I-beams by the very large number of cross beams necessary to provide adequate support for the temporary platform, especially when transferring the weight of the cast concrete whilst it is still uncured, result in very considerable transverse forces being applied to the main I-beam girders and this has been known to result in a certain amount of distortion of these main girders which results in them being under stress; this, of course, is unacceptable in a major load-bearing structure such as a bridge.

The present invention seeks to provide a falsework structure which can bear the load of uncured material temporarily from the I-beam girders of a structure such as a bridge without applying thereto forces which might risk distortion of the girders during the curing process.

The present invention is based on the surprising realisation that it is not, in fact, essential for the temporary platform to lie exactly flush with the upper surfaces of the I-beam girders, and that, consequently, this makes it possible for the upper flanges of the Ibeam girders themselves to be used as load bearing members from which the weight of the falsework, and therefore also of the uncured concrete, can be borne.

This has a very considerable advantage in that, upon removal of the falsework, the cast concrete is already supported on the upper flanges rather than its weight being distributed over the upper and lower flanges of the I-beams as with the prior art falsework described above, so that there is no change in the route by which the weight of the deck is transferred to the girders as the falsework is dismantled and removed. This also means that the falsework is easier to remove.

The present invention offers additional economies in that the structure of the individual elements may be made much simpler than that of the prior art structure which necessitated each end of every cross beam to have adjustable clamps of sufficient robustness to engage the webs of the I-beams by friction, together with similar adjustable clamps of considerable robustness on the inclined legs. Nevertheless the individual elements in the falsework of the present invention are readily dismantable and reusable to form bridge decks of other dimensions on other occassions.

According to one aspect of the present invention, therefore, there is provided a system for the support, during casting, of a deck to be cast on primary supports such as girders offering two facing edges between which the deck is to span when cast, comprising one or a plurality of engagement and suspension members for engagement on an upper face of each of the said two facing edges respectively, the engagement and suspension members having means by which transverse supports may be suspended therefrom and thus, indirectly, from the said facing edges whereby to form a structure for supporting a platform on which the said deck may be cast.

In this way the weight of the entire falsework can be suspended from the said facing edges which, in the exemplary application of a girder bridge deck, would comprise the two upper facing flanges of the I-beam girders.

Embodiments of the invention may be made in which the engagement and suspension members are so formed as to be removable after the deck has been cast. Alternatively, however, it may be arranged that the falsework apart from the engagement and suspension members can be dismantled, leaving the engagement and suspension members in place.

Suitable cladding or covering would, o & edurseyena$naliXd , of be supplied.

Likewise, in embodiments in which the engagement and suspension members are removable, it is appreciated that such removal will leave a small space between the upper surface of the facing edges of the primary supports and the overlying cast deck. This, however, is of relatively small dimensions such as not to compromise the bearing face of the primary support, and may be left as a small void, or may be filled with a subsequently-applied filler material should this be considered appropriate in order to prevent the ingress of water during inclement weather.

In the case of removable engagement and suspension members it is preferable that there be provided releasable securing means for securing the engagement and suspension members in position on the said facing edges of the primary supports prior to casting of the deck.

Such releasable securing means may take a number of different forms as will be described below.

The engagement and suspension members are preferably elongate in the direction parallel to the said facing edges of the primary supports such that, by fitting a plurality of adjacent engagement and suspension members a substantially continuous suspended support can be formed from a plurality of engagement and suspension members located end to end.

In this way the overlap of the engagement and suspension members with the facing edges of the primary supports need not be very great in order to secure adequate bearing support, thereby minimising the void left upon removal.

The engagement and suspension members preferably comprise sheet metal elements of inverted asymmetric L-section the shorter limb of which lies in use on the upper face of a primary support and the longer limb of which is adapted for attachment to transverse support suspension means by which the transverse supports are suspended from the engagement and suspension members. In one embodiment the sheet metal L-section elements are made of hardened or spring steel although other materials such as aluminium or glass reinforced plastics may be employed.

In forming the structure of the present invention the transverse support suspension means may comprise one or a plurality of channel-section members releasably attachable to one or a plurality of the said engagement and suspension members whereby to provide interconnection between the latter and respective transverse support members.

In a preferred embodiment of the invention the releasable engagement and suspension members are adapted for engagement on the upper flanges of respective I-section bridge girders, and there are provided means for locating the transverse support members against the webs of the Ibeams. Such location, however, unlike the clamping engagement of prior art cross beams, is only of sufficient resistance adequately to locate the beam against displacement transversely of the main supports or I-beam girders and does not need to be sufficiently robust to clamp against the webs thereby minimising the transverse forces which are applied to the webs and therefore to the I-beam girders.

The said releasable securing means for the releasable engagement and suspension members may comprise resilient arms bent from the material of one limb of an inverted Lsection element to define a counteracting gripping member engagable on the face of a girder flange opposite the said upper face on which the other limb of the L-section element lies in use of the system.

Alternatively the said releasable securing means may comprise clamping bolts threadedly engaged in or in a member carried by the said transverse support suspension members whereby to engage against the face of the girder flange opposite that on which the engagement and suspension members lie in use of the system.

Other releasable securing means may be employed in applications in which the main support members are other than I-beam bridge girders in forming cast deck supports for other purposes, such as in buildings.

Preferably there are further provided means for suspending an access walk way from the said transverse support to facilitate access of personnel for erecting and dismantling the falsework. In the construction of large buildings or bridges the parallel primary supports, which in the case of bridges may be the I-beam girders referred to above, may be of very substantial dimensions, for example having a flange separation of between two and three metres such that the walk way may in fact be located in the underlying space beneath the deck platform but within the flanges of the two I-beam girders.

Naturally, in order to support the cast material before curing, there is required a deck platform comprising panels supported on longitudinal deck-support members or beams extending parallel to the main supports and carried on the transverse supports which are in turn suspended from the said transverse support suspension members.

In order to facilitate removal of the engagement and suspension members after the cast material has cured, there may be provided a release liner in the form of a coating or a cladding layer of low-friction material (such a PTFE) to assist removal thereof after casting.

Likwise, for the same purpose, the limb of the inverted L-shape member which lies on the upper face of the primary support may have a wedge-shape or tapering crosssection to facilitate removal thereof from the space occupied thereby between the upper face of the primary support and the cast deck after casting thereof.

The said transverse support suspension members are preferably composed of channel-section elements the channel of which is open towards the space to be spanned by the deck to be carried by the said two primary supports. Likewise, the transverse supports may be composed of composite beam or girder structures forming a lattice-like framework of elements.

The present invention also comprehends a method of producing a cast deck between two elongate permanent primary supports, such as bridge girders, comprising the steps of: fixing to an edge of each primary support facing the other at least one and preferably a plurality of removable engagement and suspension members, suspending from these latter, directly or indirectly, a plurality of transverse supports spanning the space between the said two primary supports, supporting on the transverse supports, directly or indirectly, one or a plurality of panels to form a temporary deck-support platform on which a castable deck may be formed by casting, the temporary support assembly being supported from the upper faces of the said permanent primary supports, onto which faces the cast deck will bear, casting the deck and allowing it to harden, subsequently removing the temporary deck-support platform and withdrawing the engagement and suspension members from the spaces between the upper surface of the primary supports and the lower face of the thus-cast deck.

The step of fixing the engagement and suspension member or members to the primary supports may include introducing a release layer or lining between the engagement and support members and at least the upper surfaces of the primary supports whereby to facilitate subsequent removal after casting the said deck.

The said release layer or lining may also be formed or laid over an upper surface of the said engagement and suspension members whereby to faciliate subsequent removal thereof after casting.

Embodiments of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a sectioned, partly cut away perspective view of a falsework support structure formed as a first embodiment of the present invention; Figure 2 is a view in the direciton of the arrow A of Figure 1; Figure 3 is an enlarged sectional view of a part of the embodiment of Figures 1 and 2; Figure 4 is an enlarged sectional view of a part, corresponding to that of Figure 3, of an alternative embodiment of the invention; Figure 5 is a partial perspective view of the alternative embodiment of the invention; and Figure 6 is a sectional view of a further embodiment of the invention.

Referring now to Figures 1 to 3, there is shown a partlyformed bridge structure comprising two parallel main supports in the form of I-section bridge girders identified with the reference numerals 11 and 12 each girder comprising upper and lower parallel flanges each having a medial part facing the other girder, and a lateral part facing outwardly, away from the other girder. The girder 11 has a web 21, upper and lower lateral flanges 13, 15 respectively and upper and lower medial flanges 14, 16 respectively whilst the other main I-beam girder 12 has a web 22, upper and lower lateral flanges 17, 19 respectively and upper and lower medial flanges 18, 20 respectively.

Suspended from the upper medial flanges 14, 18 of the two I-beams 11, 12 is a falsework support structure generally indicated 23 on which an upper decking panel 24 is carried. The falsework structure 23 comprises a plurality of transverse supports or primary falsework beams 25 each in the form of a lattice girder, and supporting a plurality of longitudinally extending secondary beams 26 lying parallel to the I-beam girders 11, 12 and on which the decking panel 24 itself lies.

As can be seen more particularly in Figures 2 and 3, the primary transverse falsework beams 25 are suspended at each end from the upper medial flanges 14, 18 of the Ibeams 11, 12 by means of a suspension structure comprising elongate engagement and suspension members 27, 28 secured to respective transverse support suspension members 29, 30 in turn respectively secured to the transverse supports or primary falsework beams 25.

The engagement and suspension members 27, 28 at opposite ends of the transverse supports 25 are identical, apart from the fact that they face in opposite directions, and hereinafter only the engagement and suspension member 27 engaged on the upper medial flange 14 of the I-beam 11 will be described in more detail it being understood that exactly the same description applies to the engagement and suspension member 28.

Each engagement and suspension member 27, there being a plurality of these formed as individual elements which can be placed end to end along the upper medial flange 14 of the I-beam 11, comprises an inverted L-section element having an upper horizontal limb 31 which lies on the upper face of the upper medial flange 14 of the I-beam 11, and a depending, longer limb 33 which extends below the medial flange 14. The engagement and suspension members 27 are made from a suitable sheet metal, such as hardened steel of a type which, it has been found, exhibits sufficient tensile strength and resistance to bending to bear the considerable load of a cast concrete deck without succumbing to the forces applied to allow bending of the upper limb 31 with respect to the lower limb 33 which might allow the entire falsework structure to fall between the girders 11, 12.This is further resisted by a number of embossed "ribs" (not visible in the drawings) at the fold line where the upper limb 31 joins the lower limb 33.

Pressed from the lower limb 33 are retaining limbs 35 which engage the under surface of the upper medial flange 14 to assist in locating the engagement and suspension member 27 in position after it has been fitted and before the remaining assembly of the falsework has been secured thereon, following which it is retained in position against removal by the presence of this structure.

The transverse support suspension member 29 fixed to the depending limb 33 of the engagement and suspension member 27 comprises a channel-section element having a web 37 and two parallel walls 39, 41 which, in the orientation shown in Figure 3, comprise an upper side wall 39 and a lower side wall 41. The web 37 of the channel-section transverse support suspension member is secured to the depending limb 33 of the engagement and suspension member 27 by a series of bolts 43, any one of which is visible in Figure 3. The length of the transverse support suspension member 29 may be sufficiently great to join together several of the engagement and suspension members 27. The lower side wall 41 of the transverse support suspension member 29 is secured to the primary cross beam 25 by a bolt 45.The bolts 43 and 45 may be provided with suitable locking washers, double lock nuts or other means to ensure their secure coupling between assembly and casting bearing in mind that the structure may be subject to a certain amount of vibration due to the applied load of the equipment delivering the concrete for casting, and any concrete vibratory equipment used to deaerate the concrete before it has cured.

A release liner 47 is placed over the upper medial flange 14 of the I-beam 11, and extends around the upper limb 31 of the L-section engagement and suspension member 27, and over the upper surface of the upper wall 39 of the transverse support suspension member 29 where it is trapped between this wall and the deck panel 24. It will be appreciated that the upper surface of the deck panel 24 lies substantially flush with the upper surface of the release liner on the upper limb 31 of the engagement and suspension member 27, and that this surface is slightly higher, by the combined thickness of the engagement and suspension member 31 and to thicknesses of the release liner 47 than the upper surface 49 of the upper medial flange 14 of the I-beam 11. When concrete is cast over the falsework structure, therefore, it will follow this shape but, as will be appreciaed from Figure 1, the amount by which the bearing area of the combined upper medial and lateral flanges 13, 14 is reduced by the presence of the upper limb 31 of the engagement and suspension member 27 is negligible and does not materially affect the ability of these combined flanges to bear the load of the cast deck.

As can be seen in Figures 1 and 2, the primary falsework cross beams 25 are provided at each end with respective locating legs 50, 51 in the form of threaded struts having suitable engagement feet 52, 53 by which the struts can be turned using a suitable tool, each threaded leg 51, 50 being threadedly engaged in a correspondingly threaded housing 54, 55 at respective ends of the primary beam 25. The function of these locating legs is simply to position the primary beam 25 laterally between the two I-beams 11, 12 in order to ensure that there is no motion longitudinally of the primary beam 25 which might allow disengagement of an engagement and suspension member 27 or 28 in view of the small bearing surface between these and the upper medial flanges 14, 18.

In addition, suspended from each primary cross beam 25 by pairs of suspension ties 56, 57 are respective lower struts 58 which form supports for a platform (not shown) to make an access walk way for personnel engaged in erecting and dismantling the falsework. Each subsidiary cross beam 58 has, like the primary cross beam 25, respective screw-adjustable locating feet 59, 60.

Referring now to Figure 4 the alternative embodiment shown comprises engagement and suspension members 127 again of generally inverted L-shape form having an upper limb 131 and a depending limb 133. A channel-section transverse support suspension member 129 is secured to the depending limb 133 by a bolt 143 in a similar manner to that of the embodiment of Figures 1 to 3. In this case, however, the assembly is retained to the upper medial flange 14 of the I-beam 11 by a clamp bolt 151 passing through a lower bracket 152 welded to the lower wall 141 of the channel section transverse support suspension member 129. The clamp bolt 151 has an enlarged foot 153 at one end and an adjustment hexagon head 154 at the other, is in threaded engagement with a hole in the bracket 152 and can be locked in its adjusted position by a lock nut 155.

The transverse support 25, instead of being suspended on a bolt 45 as in the embodiment of Figures 1 to 3, has a shaped end with a projecting lug 156 which rests on the upper face of the lower wall 141 of the transverse support suspension member 129 and is retained in place by a bolt 157 passing through the lug 156, the wall 141 and the bracket 152. Otherwise the transverse support 25 may be of the same structure, that is the lattice framework structure, as in the embodiment of Figures 1 to 3.

In this embodiment the bend between the upper limb 131 of the engagement and suspension member 127 is one or two degrees less than 90 degrees, and the corner 158 is a rounded bend for increased strength and simplicity of manufacture, which also facilitates removal of the engagement and suspension members after casting, since the slight inclination of the upper limb 131 is retained by the fact that the depending limb 133 is held perpendicular by its engagement with the transverse support suspension member 129. Once this is removed and the engagement and suspension member can adopt its natural, relaxed inclination, the limb 131 can be lowered to an inclination parallel to the upper face of the medial flange 14 and withdrawn through the void which, in this case, is slightly greater in width than the thickness of the limb 131.

Referring now to Figure 5 there is shown an alternative structure which may be used in circumstances where it is considered that a less robust structure will be sufficient to withstand the forces in play during use.

Tests conducted by the applicant have established that in fact this may be the case even on very substantial bridge structures in which the I-beam girders are of the order of 10 metres or more apart. In this embodiment there is shown an engagement and suspension member 227 having an upper limb 231 inclined, as described in relation to the embodiment of Figure 4, a few degrees less than 90C from a main depending limb 233 from which, in this case, projects a lower limb 234 at an angle very close to 90".

On this lower limb rests a transverse support suspension member 229 in the form of an angle-section element having an upright limb 237 and a substantially horizontal limb 243 on which the ends of the transverse support such as the support 25 of Figures 3 and 4 may be carried.

The upright limb 237 bears a number of holes 238 by which the transverse support suspension member 229 may be bolted to a plurality of engagement and suspension members 227. It is envisaged that each engagement and suspension member 227 may be of the order of 225 millimetres in length held at 250 millimetrescentres to a transverse support suspension member 229 which itself may be of the order of 1.5 metres in length. The engagement and suspension members 227 are shorter than the transverse support suspension means 229 both to facilitate the hardening process involved in their structure, and also to facilitate removal after casting since, in this case, only relatively short individual elements need to be drawn from the void created during casting between the upper face of the I-beam flange 14 and the overlying cast deck.

Reinforcing fillets 240 are welded to the upright limb 237 and the horizontal limb 243 of the transverse support suspension member 229 and the horizontal limb 243 itself has a reinforcing depending flange 241 to which are attached, for example by welding, a series of threaded elements, illustrated in Figure 5 as the nut 242 through which may be passed a bolt the purpose of which is to engage the web of the I-beam girder and assist in locating the assembly precisely in position prior to casting.

The embossed ribs at the bend between the upper limb 231 and the depending limb 233 of the engagement and suspension member 227. These have been identified with the reference numeral 250.

Referring now to Figure 6, in which components performing the same or similar functions have been identified with the same reference numerals raised by 200, the girder flange 214 supports an engagement and suspension member 227 of modified form, which will be described in more detail below, with the interposition of a modified member 247 taking the place of the release liner 47 of the embodiment of Figure 3.

In this embodiment the release liner 247 is formed as a relatively stiff or rigid plastics element which surrounds the upper limb of the suspension engagement member 231 leaving a surrounding air gap 250. In this case the suspension support member also has a lower horizontal limb 235 projecting from the vertical limb 233 which engages an L-section suspension support member 229 which is secured thereto by a bolt 243 passing through a vertical limb 237 and 247 having a horizontal limb 241 secured, in the same way as before, by a bolt 257 to a flange 256 of the primary cross member 25.

A removable filler member 251 occupies the space defined by the limbs 237, 241 of the suspension support member and on an upper face 252 of this filler member lies a horizontal limb 253 of the release liner 247. From this horizontal limb extends a substantially vertical limb 254 which, at its junction with the horizontal limb 247 has a horizontal enlargement 255 the purpose of which will be explained in more detail below. The junction line between the horizontal limb 253 and the vertical limb 254 may be provided with regions of reduced thickness, perforations or other weakening by which the horizontal limb 253 can be separated, by the application of suitable force, from the vertical limb 254.

In use of the embodiment of Figure 6 the system works in exactly the same way as previously described, with the exception that the rigidity of the release liner enables it to retain its shape against the imposed load by the concrete cast above it, thereby maintaining the air gap 258 between the upper limb of the engagement support member 231 and the release liner 247 itself. Upon dismantling of the falsework, when the primary beams 25 and the deck 24 have been stripped away the engagement support member 231 can be removed by sliding it horizontally (to the right as shown in Figure 6) which motion is permitted by the slight degree of flexibility of the vertical limb 254 of the release liner itself.

Should it be desired the horizontal limb 253 can be separated from the vertical limb 254 leaving this projecting downwardly from the superimposed cast concrete deck and defining the same air gap 258 between the concrete and the flange 214. It may be considered desirable to fill this air gap with a setting compound or it may be considered appropriate to leave this open, in which case the downwardly projecting limb 254 acts as a barrier against the ingress of condensation formed on the underside of the deck during weather conditions favouring such condensation thereby inhibiting the risk of corrosion of the metal flange 214.

Claims (22)

1. A system for the support, during casting, of a deck to be cast on primary supports such as girders offering two facing edges which the deck is to span when cast, comprising one or a plurality of engagement and suspension members for engagement on an upper face of each of the said two facing edges respectively, the engagement and suspension members having means by which transverse supports may be suspended therefrom and thus, indirectly from the said facing edges, whereby to form a structure for supporting a platform on which the said deck may be cast.

2. A support system as claimed in Claim 1, in which the engagement and suspension members are so formed as to be removable after the deck has been cast.

3. A support system as claimed in Claim 1 or Claim 2, in which there are provided releasable securing means for securing the engagement and suspension members in position on the said facing edges.

4. A support system as claimed in any of Claims 1 to 3, in which the engagement and suspension members are elongate in the direction parallel to the said facing edges such that a substantially continuous suspended support can be formed from a plurality of engagement and suspension members located end to end.

5. A support system as claimed in any preceding claim, in which the engagement and suspension members comprise sheet steel elements of inverted asymmetric-section the shorter limb of which lies in use on the upper face of a primary support and the longer limb of which is adapted for attachment to transverse support suspension means.

6. A support system as claimed in Claim 5, in which the transverse support suspension means comprise one or a plurality of channel-section members releasably attachable to one or a plurality of the said engagement and suspension members whereby to provide interconnection between the latter and respective transverse support members.

7. A support system as claimed in any preceding claim, in which the releasable engagement and suspension members are adapted for engagement on the upper flanges of respective I-section bridge girders, and there are provided means for locating the transverse supports against the webs of the I-beams.

8. A support system as claimed in Claim 3 or any of Claims 4 to 7 when dependent thereon, in which the said releasable securing means comprise resilient arms bent from the material of one limb of an inverted L-section element to define a counteracting gripping member engageable on the face of a girder flange opposite the said upper face on which the other limb of the L-section element lies in use of the system.

9. A support system as claimed in Claim 3 or any of Claims 4 to 7 when dependent thereon, in which the said releasable securing means comprise clamping bolts threadedly engaged in or in a member carried by the said transverse support suspension members whereby to engage against the face of the girder flange opposite that on which the engagement and suspension members lie in use of the system.

10. A support system as claimed in any preceding claim, in which there are provided means for suspending an access walkway from the said transverse supports.

11. A support system as claimed in any preceding claim, in which the deck platform comprises panels supported on deck-support members or beams in turn carried by the said transverse supports which are suspended from the said transverse support suspension members.

12. A support system as claimed in any preceding claim, in which the engagement and suspension members are provided with a release layer in the form of a coating or a cladding of low-friction material to assist removal thereof after casting.

13. A support system as claimed in any preceding claim, in which the limb of the inverted L-shape member which lies on the upper face of the primary support has a wedge-shape or tapering cross-section to facilitate removal thereof from the space occupied thereby between the upper face of the primary support and the cast deck, after casting thereof.

14. A support system as claimed in any preceding claim, in which the said transverse support suspension members are composed of channel-section elements the channel of which is open towards the space to be spanned by the deck to be carried by the said two primary supports.

15. A support system as claimed in any preceding claim, in which the transverse supports are composed of composite beam or girder structures forming a latticelike framework of elements.

16. A support system as claimed in any preceding claim, in which there is provided a release liner at least partly surrounding the engagement and suspension members, the release liner being sufficiently rigid to maintain an air gap between itself and at least part of the engagement and suspension member under the applied load of a superimposed cast deck whilst curing.

17. A support system as claimed in Claim 16, in which the release liner has a downwardly projecting limb or flange spaced from the corresponding part of the engagement and suspension member and capable of acting, after casting of the deck, as a barrier against moisture.

18. A method of producing a cast deck between two elongate permanent primary supports, such as bridge girders, comprising the steps of: fixing to an edge of each primary support facing the other at least one and preferably a plurality of removable engagement and suspension members, suspending from these latter directly or indirectly, a plurality of transverse supports spanning the space between the said two primary supports, supporting on the transverse supports, directly or indirectly, one or a plurality of panels to form a temporary deck support platform on which a castable deck may be formed by casting, the temporary support assembly being supported from the upper faces of the said permanent primary supports, onto which faces the cast deck will bear, casting the deck and allowing it to harden, subsequently removing the temporary deck-support platform and withdrawing the engagement and suspension members from the space between the upper surface of the primary supports and the lower face of the thus-cast deck.

19. A method as claimed in Claim 18, in which the step of fixing the engagement and suspension member or members to the primary supports includes introducing a release layer or lining between the engagement and support members and at least the upper surfaces of the primary supports whereby to facilitate subsequent removal after casting the said deck.

20. A method as claimed in Claim 18 or Claim 19, in which the said release layer or lining is also formed or laid over an upper surface of the said engagement and suspension members whereby to facilitate subsequent removal thereof after casting.

21. A support system substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

22. A method of producing a cast deck substantially as hereinbefore described with reference to and as shown in, the accompanying drawings.