Corus Fast-track Steel Framing- Stranraer Academy - Central Circulation Boulevard

Topics Covered

Project Team

Client: Stranraer Academy
Engineer: Rennie & Kirkwood
Architect: Dumfires & Galloway Council
Area Architect: Peter Nelson
Steelwork Contractor: T A Kirkpatrick

Project Overview

They call the 400m long covered route from one end of Stranraer Academy to the other a 'boulevard'. In truth, it's a bit more like a very long grove of leaning trunks and overhanging branches with the sky filtering down between. Despite the great arboreal imagery the prosaic reality is that it's all in steel plus the asymmetrical glass vault protecting pedestrians below from the elements.

The Stranraer Boulevard is actually the circulation backbone of the school and the spine for its phased rebuilding. Running east west are large spaces such as the gym, swimming pool, auditorium on the north side, with classrooms and offices on the south. The vault is thus canted to the south allowing light through into south-facing windows and balconies in the larger spaces.

As one section of the post-war school is demolished another is built (using fast-track steel framing) along the boulevard so that by the Millennium Stranraer will have a more or less new 5000m2 school. And a wonderful tree-like spine. Dumfries and Galloway area architect, Peter Nelson, explains: "A tree-lined street seemed the most suitable metaphor. I saw the need for people in the school to meet and integrate - on this site that could only happen in the corridor. So why not make the corridor bigger and better, turn a street into a boulevard which could also be an architectural statement, a landmark to remind people that school is a very important part of the community"

Steelwork

Altogether there are 15 steel trees each with a main trunk and two main branches. Each of these in turn has four sub-branches forming the edges of an inverted pyramid interlinking on the lower side of the vault with struts attached to the buildings in the formation of pyramids on their sides. Together with the glazing bars overhead this forms an intricate, forest-like array whose appearance of informality is enhanced by the way the trees are slightly out of true. They lean 8 degrees into the middle of the boulevard and are arranged in pairs, each pair leaning 8 degrees into each other - or away from each other depending where you start. According to the architects this two-way leaning of the trees contributes to the feeling of 'naturalness' of the whole structure.

Architect’s Inspiration

Inspiration for the precise shapes included Calatrava's Lyon station and Stuttgart airport, with tubular steel, according to Nelson, "really the only suitable material for the trees" Sam Henderson of Corus Tubes (formerly British Steel's Tube and Pipe structural advisory team) at Corby helped with the engineering design analysis and later helped refine the design in optimising member sizes.

Fabrication

Geoff Kirkpatrick of fabricator T A Kirkpatrick which developed the design using the computer application Strucad, says: "The 15 trees and other framework in the boulevard is the most complex job we have ever taken on, but the design was easily broken down into elements. This type of three - dimensional structure requires the welding of angles in two planes which was initially tricky, but the welders soon became familiar with the process and the trees have hidden joints to keep the smooth appearance." In retrospect, say the designers and fabricators, they would probably have gone for bespoke cast - steel connector nodes instead of pre-formed welded pipe fitting in order to improve the impression of an organic flowing form.

Fabrication turned out to be a two - part operation. The trunks were split into two sections with the branches and their triangular connecting elements welded on. On site, the trunks were welded together and the tips of the branches HolloBolted together. When all of the trees were thus connected, the branches had become a very long, longitudinal triangular tubular truss supporting the glazing panels. The latter were intended to be planar glazing but in the end the Vitral system was selected because of fears about the effect of the exposed coastal environment.

Fire Protection

Because it is a single-storey structure, the boulevard itself doesn't need fire protection, but it does need to be smoke - compartmented. So there are sheets of glass hanging down from the branches at two locations, dividing the boulevard into three compartments.

Source: Corus

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