Glentrool bridge

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What is it?

A 7m span x 1.5m wide steel and timber bridge which can be used in many path situations. Originally designed and developed by Forestry Commission's Forestry Civil Engineering as a replacement for the 'Galloway' timber and steel bridges, it is simple to build and install whilst being more durable.

glentrool bridge oatridge college

How does it work?

The Glentrool bridge is made from steel universal beams and bolted-on angle transoms, with a timber decking and parapet. In between the handrail support posts, vertical timber slats provide a more secure side to the bridge. Timber nailing strips are bolted on top of each universal beam for fixing the timber decking boards. The steel frame, made from universal beams and angle transoms, can be prefabricated off site, galvanised, and then delivered to site for installation. Good access is therefore essential. Where access is very good for lifting equipment, such as a large excavator or crane, the fixing of all timber components, like the decking to the frame, can be completed before lifting the bridge onto its concrete abutments or end seats. Where access is more difficult (like the site at Oatridge College), the steel frame would be lifted into place first, using the easiest and safest method of installation. Then the timber decking, parapet etc. would be fitted to the steel frame to complete the bridge.

Is it suitable?

The Glentrool bridge is suitable for all path users, and for a range of spans from 2m to 8m.

How much will it cost?

Depending on the bridge span and width, the height of the parapet and other factors like access, the Glentrool bridge with galvanised steel frame may cost £5,000 - £20,000.

How do you install it?

The construction sequence is different for off-site fabricated and on-site fabricated bridges.

Off site fabricated bridge:

The whole bridge is prefabricated and built off site and transported to site ready for lifting in place, using a large excavator or crane that can easily gain access to the bridge site.

  • Construct bank abutments and approaches on site ready for bridge installation.

  • Lift in and bolt down the bridge's steel frame on to the abutments.

  • Screw down anti-slip strips or flat sheets to the decking boards. Alternatively, install decking boards with pre-fitted anti-slip strips.

On site fabricated bridge:

The steel beam and angle transom frame is fabricated off site and transported to site ready for lifting in place using an excavator that can easily gain access to the bridge site, where a crane cannot. The decking boards and parapet components etc. are installed to the steel frame on site. The safest method is to install the decking boards, parapet components etc. together, working across the bridge from one side to the other.

  • Construct abutments and approaches on site ready for the bridge installation.

  • Lift in and bolt down the bridge's steel frame only on to the abutments.

  • Bolt on nailing strips. If the bridge spans an inaccessible crossing, such as a deep gorge, the nailing strips should be bolted to the steel frame before it is lifted in for safety.

  • Nail or screw down the decking boards onto the nailing strips.

  • Bolt on the handrail posts to the top and bottom angle transoms.

  • Screw on the handrails and kick boards.

  • Screw in vertical timber slats to the inner handrail and kick board between handrail support posts, and then attach outer rail.

  • Screw down anti-slip strips or flat sheets to the decking boards. Alternatively, install decking boards with pre-fitted anti-slip strips.

glentrool bridge end view oatridge college

What variations are available?

Timber nailing strips are prone to decay where decking board nails or screws are driven in. Instead of timber, consider using recycled plastic for nailing strips. It will last longer and will not rot.

Under trees, timber decking boards can become very slippery from algae growth caused by continuously wet timbers or decaying leaf litter. Again, instead of timber, consider using recycled plastic for a bridge deck that inhibits algae growth and has a rough surface texture, providing some grip. However, recycled plastic is heavier than timber, a little more expensive and more flexible – for wider bridge widths, recycled plastic decking boards would need extra strengthening.

Find out more...

For comprehensive information about all elements of bridge planning, design and construction check out the icon Path Bridges Guide. The guide also contains standard designs for other bridge types such as Log Bridge, Sawn Timber Bridge, Glentrool Bridge - Timber.

Detailed drawings - Glentrool bridge

If you like the look of the Glentrool bridge at Oatridge College as a potential bridge design for your project, download the various detailed drawings below:

icon Glentrool Bridge Steel - General Bridge Layout Plan & Elevation View

icon Glentrool Bridge Steel - Concrete Abutment Plan & Elevation View

icon Glentrool Bridge Steel - Optional Bolted Transom Detail

© 2014 Paths for All - Registered Scottish Charity No: SC025535, Company Limited by Guarantee No: 168554 inc. 19 Sept 1996 at Companies House, Edinburgh