Ferndale Middle School Roof
The Ferndale School project, built in 1999, marked a milestone in our company's development, as it was our first project outside of Canada, and it allowed us to establish our American affiliate, StructureCraft Builders USA Inc.
The roof for this project utilizes “peeler cores" in a 3-dimensional space frame roof structure. Peeler cores are the remaining wood cores after the plywood veneers have been peeled off. The low cost and compression capacity of these members coupled with cast steel connectors combine to produce a unique exposed timber roof structure.
In this case we were brought in to fabricate and erect the 15,000 square foot roof, a seven foot deep Takenaka space truss, consisting of over 2200 approximately eight foot long round Douglas Fir peeler core members, with special dowel fittings at the ends, connected to ductile iron castings at the nodes, of which there are 650.
The roof is supported by a number of concrete columns and branch supports, consisting of four 10 inch diameter peeled logs at each location. Roof cladding is 1 1/8 inch thick plywood, in 4 ft. by 12 ft. sheets.
The 5 inch diameter members with their fittings were fabricated in our shop and shipped to site, where we had erected scaffolding and decking below the whole roof area to suit the pitch of the roof, which is a flat plane tiled at 1 in 12. Scaffolding at the high end was up to 35 ft. high.
The architect and engineer already had a design for the roof, and StructureCraft operated more like a conventional builder. However, we are engineers and never like to stop thinking, so as we went about the project we developed a number of design and erection ideas. These included the concept for creating a work platform that would solve the fit-problems inherent in the highly redundant design, and also eliminate the need for large cranes and fall-arrest provisions for workers. We devised “chairs" which would prop up the node casting at the exact location and allow access for all the bolted connections within it.
We also refined the node castings to simplify erection. The extra work put into this design was more than compensated for by the resulting improvement in the erection speed.
The idea was to ensure there were no fit problems in the highly redundant structure, and thus to start the assembly of the pieces at one end, and move in a “wave" towards the other end. In order to control installation error, specially designed chairs placed on the scaffolding were surveyed into location for both height and placement, allowing each bottom node location to be compared to the theoretical as the erection progressed. If small errors were found, they were immediately dealt with using shims which lengthened or shortened the member lengths slightly. This proved to be a very reliable and expedient technique, and erection proceeded quickly. Portions of the scaffold were removed to allow installation of the branch supports below, following which all of the scaffolding was removed.