There are many ways in which the formation of bridges can be completed on site, and which usually require the laying of metal or reinforced concrete support beams to span the gaps between vertical supports (e. g. reinforced concrete columns and end abutments) and followed by laying or forming a bridge deck on the support beams. A bridge deck can be assembled from a number of pre-formed cast slabs of reinforced concrete, or alternatively the slabs can be cast in situ on temporary shuttering supported by the support beams.

It is also known to form the support beams, and the deck, entirely from metal fabrications, and which are assembled on site e. g. by bolts, rivets etc to complete the formation of the bridge on site.

Alternatively, it is known to pre-form metal deck modules which are transported to site and then simply assembled end to end on suitable vertical supports to complete the formation of a required bridge structure. Deck modules of this type are particularly suitable for military use e. g. the well known Bailey bridges, in which it is very important to complete the formation of a bridge in a short period of time, although such modules can have widespread civilian use also.

The present invention is concerned primarily with a pre-formed bridge deck module which can be manufactured remotely, be transported to site, and then readily assembled on site to complete the formation of a bridge deck span between two supports.

Remote manufacture of a deck module in a factory or compound allows careful quality control to be exercised (and without exposure to the weather), and then simple assembly on site completes the formation of the deck, usually involving more than one module.

According to the invention there is provided a pre-formed deck module which comprises: a pair of longitudinal support beams which are laterally spaced from each other; and, a deck slab of reinforced concrete, said slab being united with the support beams to form a transportable module which can subsequently be laid on two or more supports on site to form a bridge span between the supports.

The invention therefore provides a pre-formed deck module in which the deck slab acts compositely with the support beams so as to resist all loads applied in service, which will include the dead load of the module and any design live loads.

Preferably, the support beams are metal beams, though other materials used in construction work may be employed including reinforced concrete beams, and pre and post stressed concrete beams.

When metal support beams are used, they will preferably be steel beams with a web and at least one flange e. g. a T-beam, or an I-beam. Any suitable means may be used in order to unite the deck slab with the support beams, although one preferred arrangement comprises shear connectors secured to the beams e. g. to the top flanges and embedded in the cast concrete of the deck slab. The shear connectors are arranged so as to prevent relative longitudinal movement between the beams and the concrete slab under load (permanent and live). The shear connectors may be in the form of studs, steel sections, hoops, or any other suitable shear connection.

The minimum size of bridge deck which can be constructed, using the invention, will involve use of a single pre-formed bridge deck module according to the invention.

However, in practice, usually more than one module will be assembled on site to provide a required length and width of bridge span e. g. modules assembled side by side and end to end.

To form a composite bridge deck span composed of a plurality of deck modules, it will be desirable to extend the internal reinforcement of each cast deck slab laterally and /or longitudinally of the slab, so that adjacent modules can be united or integrated with each other by casting concrete on site into marginal connecting regions defined between the modules.

A preferred embodiment of a bridge using pre-formed bridge deck modules according to the invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a plan view of a bridge deck span assembled on site from a plurality of pre-formed bridge deck modules according to the invention; Figure 2 is a view from one side of the bridge deck span; Figure 3 is a sectional view of the bridge deck span, along the line of the abutment; and Figure 4 is a cross section taken on the section line A-A in Figure 1.

Referring now to the drawings, there is shown a bridge construction which has been assembled from a plurality of pre-formed bridge deck modules, in which the modules have been manufactured remotely in a factory or compound and without exposure to the weather, and in which each module is capable of being transported to site, and then assembled to form the required length and width of bridge deck span.

The preformed bridge deck modules are assembled side by side, and end to end, to form the required bridge span. However, in a minimum application of the invention to the formation of a bridge span, a single preformed bridge deck module may be utilised.

Referring now to the drawings in detail, Figure 1 is a plan view of a bridge structure designated generally by reference 10 and which comprises a bridge deck 11 which forms a single span between end supports 12 and 13, as shown in Figure 2. A typical preformed bridge deck module according to the invention is shown by reference 14, as shown in Figures 3 and 4, and comprises a pair of longitudinal beams 15 which extend parallel to each other, but are laterally spaced apart as shown. A deck slab 16 of cast concrete with metal reinforcement is united with the support beams 15 to form a transportable module which can subsequently be laid on two vertical supports on site (e. g. the end abutments 12 and 13) to form a bridge span between the permanent supports. The support beams are preferably made of metal, though other materials used in civil engineering may be employed, including reinforced concrete, and pre and post stressed concrete.

The deck slab 16 comprises concrete cast around metal reinforcement in a remote location, and at the same time being united with the support beams 15 to form a composite structure. Thus, the deck slab 16 acts compositely with the support beams 15 so as to resist all loads applied in service, which will include the dead load of the module (the beams plus the reinforced concrete slab), and any design permanent and live loads.

The metal support beams 15, as shown in the drawings, are steel beams with a web and at least one flange, and in the illustrated arrangement comprise steel I-beams having a narrow top flange 17 and a wider bottom flange 18.

Any suitable means is used in order to unite the deck slab with the support beams, although one preferred arrangement comprises shear connectors secured to the beams e. g. to the top flanges 17 and embedded in the cast concrete of the deck slab. The shear connectors are arranged so as to prevent relative longitudinal movement between the beams 15 and the concrete slab under load (permanent and live).

The shear connectors can be in the form of studs, steel sections, hoops or any other suitable shear connections.

The beams 15, if steel, can be standard rolled sections, or fabricated sections, comprising at least a single flange and a single web.

Prior to casting of the concrete slabs 16 to be united with the support beams 15, each beam is supported, and may be pre-cambered or straight. If pre-camber is required, this may be achieved either by pre-stressing the beam eccentrically, heat treatment, rolling, fabricating or any other method which does not result in adverse stresses being introduced into either the steel beam or the cast concrete.

In order to ensure distribution of loads between adjacent modules, transverse and longitudinal reinforcement in each deck slab may project a short distance horizontally, in the form of a hoop or other shape which ensures sufficient bond between the reinforcement and a subsequently formed in situ strip of concrete, as shown by reference 19 in Figures 3 and 4.

After casting of each slab 16, the modules are moved either to storage, to site or to their final position, but only after the cast concrete has achieved sufficient strength to ensure composite action between the beam and concrete slab components of the module.

If bearings are to be used the deck modules are placed onto these bearings which are located on permanent or temporary supports, or alternatively the bearings are attached to the beams prior to placing the modules onto the supports.

The bearings may be located under the longitudinal beams (15), or under transverse beams located between the main longitudinal beams.

After the modules have been positioned (side by side and/or end to end), the strip between each adjacent module can be made integral with the pre-cast deck slabs 16 by filling with concrete, if required.

Prior to infilling with concrete reinforcement is threaded through the projecting reinforcement between modules to prevent differential shrinkage cracking and ensure that differential movement does not occur between adjacent units.

A pre-formed bridge deck module according to the invention can be used for a short span bridge deck, requiring only a single module to link each end of the structure, in a minimum application of the invention. However, a plurality of preformed deck modules according to the invention may be joined both transversely and/or longitudinally on site, to form long multi-span bridge decks on site.

In order to reduce the stresses in the steel, leading to economies in steel usage, and to reduce the mid-span deflections due to dead load, the ends of the beams 15 may be set on temporary packs prior to pouring a transverse joint concrete strip and making a splice in the steel beams. When the splice in the steel is complete and the concrete has achieved sufficient strength, the temporary pack can be removed and the deck set to its finished level, resulting in a"hogging"bending moment being induced in the deck over the intermediate support. This is a preferred option, but is not mandatory. The amount of induced moment can be varied to suit the prevailing conditions for each bridge.

The span configurations, beam sizes, module lengths and widths can be determined to suit specific bridge requirement and on site variables.

The shear connectors used to connect the concrete slab to the beams are all chosen to suit the required loading and, a site contractors preferred method of working.

The splicing of steel beams in long bridge decks, where it is not possible to transport a module in one long section, may be by welded, bolted, or other connection, again to suit the site contractors method of working.

Pre-camber in the beams, if required, may be induced by any method including those described above, although again final choice will be made to suit contractors\' preferred method of work.

In order to reduce the total construction time, many of the finishings may be applied to the modules prior to installation onto the supports, including bridge deck waterproofing and parapets.