SLT Bridges

Stress Laminated Arch Footbridges are made from short lengths of plantation timber cut and drilled and then pressure treated before assembly. Laminates are generally 1500 – 2000mm long and depths up to 250mm and always 50mm wide. The laminates are threaded onto the stressing bars which are tension jacked to create what is effectively a single solid mass of timber. The exact analysis and design involves a number of factors dependant on arch shape, slip, friction, tension, end bearing etc. Economic spans are in the range of 10m to 25m.

Glue and Screw

Glue and Screw timber bridges are made in the form of flats or arches. Instead of tensioning the timbers using reinforcement bars they are vertically laminated using glue and screws between each row of laminates. The design is very much the same as for Stress Laminated bridges. They are economic from 3m to 16m span.

Aerial Mast

Aerial Mast bridges are made from steel triangular truss sections originally made for phone masts. Using the masts as bridges was patented mare than 20 years ago. Many hundreds of these bridges, with timber decks, have been built since. They are lightweight and every piece can be carried to a remote site. Because the manufacturer of the mast sections will only make those than can carry 5kN/m2 to suit Local Authority loading I have developed a new range of truss footbridge taking all the advantages of this system and designing out the disadvantages.

Glentrool

The Glentrool design is a Forestry Commission replacement for its Galloway design of the 1980’s. The original Galloway design was published by the Countryside Commission and amateur builders wrongly used the details to create dangerous structures. The bases of the design was to create a handrail system fixed to beams without puncturing the beams. I retained and improved that in the Glentrool design which is ‘idiot’ proof and was published in the book Path Bridges. Many hundreds have been built over the lst 20 years

Timber Beams

Timber beam bridges now use the Glentrool design to support the handrail system and create the lateral diaphragm restraint. These are only used up to a span of about 4m as there are more economic ways to support a deck and large timbers for beams are not readily available today.

Cable Supported Bridges

Cable supported bridges are for long spans over 25m. Many years ago suspension bridges were the choice for longs spans on Country Estates but today these cannot be built economically within the Health and Safety standards. Cable stayed support is viable and best used as part of a launch system for long spans. The high costs of these long span bridges mean that they are not often built.

Specialist

Specialist footbridges are general systems which use available beams. One example is the Hornbeam which is a World War truss used for loading tanks onto ships and some are still around for re-use in the countryside. There is the famous bucket bridge which is a cable structure not to be recommended for normal design so is not down as a standard. The bucket is suspended from the cable and the person pulls himself across the river.