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Highway Bridges Standard Steel Over-Truss Bridges

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

REIDSTEEL - DESIGN AND CONSTRUCTION OF STANDARD STEEL OVER-TRUSS BRIDGES FOR ROADS AND HIGHWAYS

The construction and design of REID steel over truss bridges mean that the effective span of the bridge is between 25m to 100m.

The Carriageways are supported by pairs of trusses at 1.7m centres. A carriage way may therefore be 5.1m overall wide, with 1.2m walkways both sides. The carriageways may be wider in increments of 3.4m; and may always be extended widthways in increments of 3.4m. There is an element of choice in the marked carriageway widths and the widths of the walkways. The minimum over truss bridge will be single lane with a 4m marked roadway.

They will have local Reinforced Concrete decks 0.275m thick, placed on our lost formwork decking with no propping needed. They can have 0.05m of surfacing. The concrete will become composite with the steel via shear connectors.

Our designs have steel crash barriers on both sides of the carriageways. The walkways will be outside the crash barriers and will have handrails on the outside.

The Bridge Decks are carried by 2 or more pairs of trusses below deck level. There is no steel above the deck other than barriers. Please note that the roadway will have to be at a height well above the flood level: as a guide the depth of the trusses is about 8% of the span, and the roadway is above this truss.

The truss bridge decks are 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. All spans are simply supported.

There are two walkways, both outside the main trusses, 1.2m wide, with handrails outside. The pedestrian, handcart and cycle traffic using them is protected from the vehicle traffic by the crash rails.

The decks of the walkways are local reinforced concrete 0.125m thick placed on our lost formwork decking.

The truss 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.

We design our 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. All the structural designs are done in house by Reidsteel.

All the steel work is hot dip galvanised 85microns, 610gm/m2, for long low maintenance life.

Construction of the bridges can take place 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 for 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 design of the truss bridges means that they 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.

If you choose to use Reid Steel for the design and construction of your bridge our work carries a ten year warranty.

UTILSATION:

An over truss bridge is economical for spans of 25 to 100m. It is essential if the bridge is to have widthways extension. If through-truss or stayed bridges are not wanted for architectural reasons, over-truss bridges may be selected. It is easy to run services under the carriageway. It is relatively easy to cantilever launch as long as there is a run up on the home bank of about 110% of the span. Because only one pair of trusses needs to be launched at one time, the launch process is simplified. The over-truss bridge is good for multiple spans. BUT note that the carriage way will be higher than the abutments by about 8% of the span, which may mean big embankment approaches.

photo of steel through truss bridge

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

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