Canadian Consulting Engineer

Roofs at Anspayaxw School in Kispiox, B.C.

Category: Buildings and StructuresThe Anspayaxw Band wanted their new school in Kispiox, northern British Columbia, to reflect the local, historical bridge building method of the Gitskan natives. This...

October 1, 2000  Canadian Consulting Engineer

Category: Buildings and Structures

The Anspayaxw Band wanted their new school in Kispiox, northern British Columbia, to reflect the local, historical bridge building method of the Gitskan natives. This clever, yet simple method consisted of cantilevering logs from each side of a canyon, and counterweighting them with rock and timber rubble at the embankments. Additional logs were then hung between the log ends to complete the span. After the 1870s, the bridges were strengthened using discarded telegraph wire.

As structural engineers for the school, Fast + Epp had to modify this traditional sagging design and create a roof that could handle snow loads up to two metres deep. A further challenge was to develop a connection system that was economical and simple to construct so that Band members could easily fabricate and erect the structure.

Early in the design phase it was decided that the large 45 metre x 20 metre multi-purpose room was the most suitable place to express the early bridge building technique. The multi-purpose area includes the library and talking circle, and is flanked by corridors and classrooms. The “embankments” were effectively created by positioning support columns at both sides of the corridor, with two interior, visible columns being 400-mm diameter turned logs. Rafter logs were then placed over these columns and cantilevered toward the middle of the space.

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The “bridge” was then strengthened with 38 mm diameter steel rods and 225 mm diameter log struts in order to provide the necessary support for the heavy Kispiox Valley snow loads and prevent the roof from sagging. The tension rod/log strut system is three-dimensional to provide both stability and aesthetic appeal. The detailing has to accommodate significant log shrinkage over time.

The band building committee was so enthusiastic about the scheme they promptly requested a similar design for the roof of the gymnasium. Here a hybrid version of the multi-purpose area roof was developed, consisting of spanning pairs of log-tension rod trusses between the perimeter walls, and a tubular steel space truss under the roof ridge.

Although there were differing load connection conditions at various points in both the gymnasium and multi-purpose room roofs, the engineers developed a family of typical connections. Thus they were able to economize on these details, simplify their erection and at the same time create a uniform architectural effect. For example, they developed unique pipe connectors at the intersections of rafter columns and tension rods.

The final result, completed in 1998, is a project that afforded native carpenters an opportunity to build in a way that has a historical link to the past, and a building that has a warm, natural ambience for the Kispiox native community. Moreover, by developing the uniform detailing and by designing an economical, prefabricated roof structure over the non-visible roof areas, the team was able to keep the structural costs within budget. The overall budget of the school was $5 million.CCE

Project name: Anspayaxw School, Kispiox, B.C.

Award winner: Fast + Epp, Vancouver (structural engineer)

Project team leaders: Paul A. Fast, P.Eng., Eric Karsh, P.Eng., Rod Maas

Client/owner: Anspayaxw School, Kispiox, B.C.

Prime consultant: Homefree Construction Management Services/ Jeff Holland (project manager)

Other key players: Larry McFarland Architects (architect), Heatherbrae Construction (contractor)

Roofs at Anspayaxw School

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