Trailer Converts into Bridge

Deep in a NSW State forest, accessible only by a narrow track winding its way up and down the steep terrain, the problem was not so much constructing this bridge but transporting it to site.

Apart from a helicopter, a 6 wheel drive truck towing a trailer was the only feasible method. Maximum weight for any component was limited to the 4 tonne lifting capacity of the caterpillar tracked hydraulic excavator. Maximum length for the trailer, dictated by the sharp bends and steep changes of grade, was 9 metres.

Since the bridge was 21 metres long, the pair of galvanized steel girders each had to be made in three parts, 6, 9 & 6 metres long, with bolted joints. Special pads were added to the girder sections, enabling them to be bolted in pairs to a truck axle and also to a tow coupling at the front. This formed a trailer chassis, able to carry one of the 9 concrete deck slabs. With another deck slab on the 6 wheel drive truck the entire bridge, including gabion (steel mesh rock cage) abutments, was transported to site in five trips.