GLULAM BRIDGE CHOICE IN HIGH CORROSION ZONE
THE Dillman Bridge in Meaghers Grant, Nova Scotia, has been decommissioned for over two years, after a truck accident on the bridge deemed the bridge unusable. For nearly 100 years, the bridge crossed the Musquodoboit River, connecting many small communities. Without it, an estimated 1400 households in the region are forced to take lengthy detours.
Irrespective of the accident, the concrete and steel structure was unable to survive the harsh weather. The bridge is located in one of the highest exposed and embedded corrosion zones in Canada.
The province put out a tender for bridge replacement – supply, design and installation – which was won by Timber Restoration Services along with Wood Research and Development.
The timber structure is 35 m long by 7.6 m wide and is designed for a load rating of CL-625 (62.5 tonne). It has a TL-4 crash proof rail system and an Alaskan yellow cedar handrail. The substructure consists of driven timber piles with a glulam timber back wall specifically designed for timber bridges.
The superstructure comprises glulam laminated deck panels sitting on eight glulam girders which have two fixed end-moment connections that were assembled on-site. The use of High Strength Fibre and advanced techniques make this light-weight option not only a cheaper alternative to that of its competitors, but it also provides additional longevity. The beams are 1.56 m deep.
Prior to the timber arriving on site, it was manufactured and assembled in a state-of-the-art manufacturing facility in Jefferson, Oregon, prior to treatment. This allowed treatment uptake to take place in all bolt fastener holes, as well as pre-drilled lag holes.
All fasteners where possible are horizontal or vertical from underneath to help moisture penetration into the bright wood. The structure was then disassembled and sent away for pressure treatment with an oil-based product. This method not only expands longevity of the structure but it also allows for an accelerated schedule during installation on site.