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Highway Bridges Bespoke Steel Through Truss Bridges

steel through truss diagram side view steel through truss diagram end view


Effective spans 15m to 100m

Carriageways can be defined by you, using the width between crash barriers.

They will usually have local Reinforced Concrete decks 0.25m thick, placed on our lost formwork decking with no propping needed. They can have 0.05m of surfacing, or for a temporary or re-locatable road bridge you can have anti-skid steel decking.

They usually have three levels of steel crash barrier on both sides of the carriageways so that neither trucks nor their payloads can hit or damage the steel trusses.

The Bridge Decks are carried by 2 trusses at, and above, deck level. These two trusses are stabilised with a bracing system: on bridges above 40m span, this is usually above the deck (closed top through-truss) on smaller spans the bracing is with rakers from the transoms.

The bridge decks are usually cambered from side to side using pre-cambered steel transoms; and slightly cambered from end to end using the built in camber of the trusses.

There can be two walkways, both outside the main trusses, as wide as you like, with handrails outside. The pedestrian, handcart and cycle traffic using them is protected from the vehicle traffic by the crash rails and main trusses.

The decks of the walkways are local reinforced concrete 0.125m thick placed on our lost formwork decking; or can be in anti-skid steel deck.

The bridge steel is entirely bolted together using regular high strength tension and shear bolts. There are no friction grip bolts. Most of the main connections are end-plated. Adjustment is by means of steel packs which can be inserted between end plates.

The bridge steel is all in pieces which can easily be transported in 20ft or 40ft containers, or on regular road vehicles.

The bridges are designed to British Standard BS 5400 for any number of lanes of full highway loading, and for 30 units of HB loading, equivalent to an occasional 120 tonne truck; or you can specify your loading system. All the structural design is in house by Reidsteel.

All the steel work is hot dip galvanised 85microns, 610gm/m2, for long low maintenance life, or you can specify your coating system.

The bridges can be erected in-situ on a temporary causeway or on temporary jackable props; or may be built on the 'home bank' and Cantilever Launched across the gap. For the cantilever launch, a 'Launch Kit' is needed, consisting of sets of rollers, a steel 'launching nose' fitted to the leading edge of the bridge (and removed fro re-use after launch), and come-along cable jacks.

The bridges will sit on our elastomeric bearings on your abutments. Expansion joints for the roadway are provided at both ends.

The bridges may be combined with other bridges to make multi-span crossings. Again the bridges can be built in-situ; or they can be cantilever launched. For multi-span bridges which are to be cantilever launched it is necessary to use a 'Link Kit' which consists of further sets of rollers, and further jacks, and a set of link steelwork which joins adjacent bridges during the launch and roll-out. As with the Launch Kits, the Link Kits can be used again and again. You will need one Link Kit for a 2-span bridge and 2 Link Kits for a 3-span bridge and so on.

Our work carries a ten year warranty.


A through-truss is probably the most economic bridge for spans 15m to 100m. The carriageway is only about 1.2m above the abutment. A cantilever launch is relatively simple as long as there is a run up equal to 110% of the span is available on the 'home' bank. Or the bridge can easily be built on a causeway in-situ during a dry season. The bridge is good for multiple spans. But a through-truss bridge cannot be extended widthways, except by building another parallel bridge.

photo of steel through truss bridge

To find out more about your Through Truss Bridge specific requirements, please complete our Highway Bridge Enquiry Form.

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