Chilliwack Secondary School
The public areas of this 3-storey secondary school - atrium, library, gymnasium and entrance canopies - all feature a wide range of architectural exposed timber structures: fluted Nail-Laminated Timber (NLT), built-up Mechanically-Fastened CLT (MF-CLT), hybrid timber-steel kingpost trusses and lathe-turned timber columns. We were invited in September 2010 by the Graham-Dialog design-build team to engineer and build the timber structures: the roofs of the atrium/multi-purpose room and library, the main entrance canopy, later on the gym trusses, and then the low canopy and bus & bike shelters. All told, a total of 34,000sqft of unique timber structure.
As a design-build project, close collaboration was needed between the architect, general contractor, and ourselves in order to ensure a cohesive design process which took into account the client's and architect's design intent while ensuring the project was constructible and remained on budget. Graham and Dialog depended upon us specifically for our experience in design, engineering, and building with wood. Our past projects had demonstrated that the solutions we came up with would not only be feasible to construct, but would also meet the structural and architectural intent, and be aesthetically complementary to the entire school.
Examples of our responses to the challenges we faced:
Early in the project we created a full 3D parametric model of the project. This model was a true building information model (BIM) used for quantity takeoffs, for procurement, to drive our shop drawing and manufacturing process, and to coordinate with other disciplines.
The atrium/multipurpose room needed to fit between two buildings that were not parallel and had different edge conditions, requiring in a warped roof, with every truss unique.
The constantly changing roof geometry meant that using a standard casting for the connections in the trusses would not suffice. Instead, we came up with a unique casting design which accommodated the various angles of the structural members.
The necessity for a large 2-way cantilever at the corner of the library and the long spans between trusses required us to design and develop a special deep version of our mechanically fastened MF-CLT panel.
"The Chilliwack secondary school project triggered two silver winners, which is really, really impressive" Fiona Famulak, president of VRCA
Fabrication & Installation
We approached this project understanding the complexities which were inherent in the tight schedule and complex designs, and so moved quickly towards a system of prefabricating components, for example:
Our experienced carpenter crews built the fluted (alternating 4” and 6” lumber) NLT roof panels in our shop as long 8’-wide strips, shipped them to site, and “draped” them into place onto the trusses, allowing them to take on the final warped shape.
The Mechanically-Fastened-CLT roof deck for the library was shop-fabricated as 12 large panels which were then shipped to site. The heavy (9-ply, 8’x40’) panels were then carefully hoisted into place on top of the glulam columns, beams and trusses, and “stitched” together with screws and infill sheathing to form a solid wood roof slab capable of carrying snow loads and in-plane seismic loading.
The kingpost trusses for the multi-purpose room/atrium (30’-55’ spans) and library (65’ span) were completely shop-assembled, shipped to site and erected in one piece. Due to the length of the gym trusses (85’ span), however, we only partially assembled them in the shop - we staged the prefabricated truss components on site until near time of installation, then completed the cable installation and erected the trusses onto the two gym structures.