Industrious Integration

The prescriptive nature of our building codes and the different standards they set for combustible and non-combustible construction have long deterred the use of structural systems that employ timber elements in combination with non-combustible materials such as steel.

As a result, Canada can be said to have two distinct architectural traditions: one, consisting of all-timber buildings, has relied heavily on the flexibility of site construction; the other, consisting of non-timber buildings, has more readily incorporated advanced technology and prefabrication techniques. But there are signs that the barriers are coming down. The move to performance-based codes has begun, and the wood industry has introduced new engineered wood products (EWPs) whose dimensional stability and predictable performance facilitate integration with other industrial materials. Five of the 13 Skytrain stations on Vancouver’s Millennium Line with innovative wood and steel structures are recent examples of the growing trend. (For a complete listing of the 13 stations and their architects, see CA July 2001.)

While architects may provide the initial impetus, it is ultimately specialist building code consultants who make it possible to use wood in applications where it is not permitted by current codes. For the B.C. stations, credit must first be given to Locke McKinnon Domingo Gibson whose negotiation of equivalency gave the architects the opportunity to use the same materials as their 19th century predecessors. Equivalency was granted on three conditions: wood could only be used for roof elements, to minimize fire load at the platform level; structures must be open-ended to prevent smoke build-up; and members must conform to minimum dimension provisions for heavy timber.

Out of necessity transit stations share a standard functional template related to passenger capacity and the characteristics of crowd movement. In addition, for reasons of economy and system identity, elements such as elevators, escalators, platform lighting and signage are also standardized. For the Millennium Line, a 1.25-metre planning grid was used for all stations. Suspended ceilings were eliminated by running all overhead services in a single pendant bulkhead with predetermined suspension points. With this standardization having its greatest impact in plan, a range of solutions have been developed in section that successfully articulate the complementary roles of wood and steel. Based on design parameters agreed upon by all the design teams, wood elements are kept above a three-metre datum to discourage vandalism, and are protected from weather.

Two architecture firms worked with structural engineers Fast and Epp, whose four stations are testimony to that firm’s creativity and versatility. Renfrew and Rupert, designed by Baker McGarva Hart Architects (now VIA Architecture) are located in a light industrial area of East Vancouver destined to become the city’s new high-tech corridor. Conceived as sister stations, they are outwardly similar but differentiated in detail. Both draw their palette of materials from the industrial and railway-related heritage of the area. Hollow steel section columns support glulam ribbed roofs clad in profiled metal decking, while fully glazed double-height curtain wall ticket halls anticipate the future context of high-tech office development. Symbolizing the movement of passing trains, the wing-like platform canopies of both stations are offset in plan, giving a dynamic quality, whether approached by road or rail. But this is where the similarities end. Renfrew is a bold and muscular structure true to industrial tradition, whereas Rupert is delicate and more finely crafted–reflecting the texture of its site adjacent tree-lined Still Creek.

At Renfrew, the canopies are supported on pairs of curved glulam ribs that cantilever from perimeter HSS Y-columns set at 10 metre centres. At their deepest, the glulams measure 760 mm, tapering in an airfoil section toward the free edge. The Y-columns support a continuous HSS eave beam that reduces in cross-section as it passes through each rib. Full load transfer at these bearing points is achieved through a concealed knife plate and saddle. This gives a subtext to the structure but ensures that visible connections are clean and simple. Here, and similarly at Rupert station, the emphasis is on the pure expression of form and materials.

The glulam ribs, complete with embedded plates, were fabricated in Alberta. Site assembly was straightforward, each module or bay comprising a Y-column, a five metre long section of the HSS eave beam, and two glulam ribs. The completed canopies present clean, strong lines, with the free-standing cantilever design ensuring that no structural elements cross the guideway.

By contrast, at Rupert station the simple cylindrical perimeter columns are set at half the spacing used at Renfrew. They each support similarly curved but considerably shallower glulam ribs that in turn support glulam purlins and a standing seam metal roof. Above the tracks, the longitudinal opening that separates the two roof canopies is bridged by steel knife plates that connect the opposing pairs of glulam ribs. At the outside edges of the roof, diagonal glulam braces complete a moment frame system that is repeated along most of the platform. The architectural language is consistent throughout the building, with steel used where the structure is protected from weather, and wood used where it is not.

Where the canopies are offset in plan, the moment frames give way to a propped cantilever similar to that at Renfrew. Here the ribs are paired, and have a continuous steel flitch plate between them. The overall width of this composite glulam and steel rib is equal to that of the single glulams used elsewhere along the platform. For visual consistency, these single ribs have a reveal routed into their lower face. This reveal also provides a concealed suspension point for the platform lighting and signage. As at Renfrew, connections are designed for minimum visual impact, with concealed plates and custom narrow-head pins countersunk into the timber members. The glulams are spruce, chosen for its light appearance.

Heading east into Burnaby, the next two stations on the line are Gilmore and Brentwood Town Centre, both designed by Busby + Associates Architects. While Rupert and Renfrew are conceptually similar, Gilmore and Brentwood differ significantly.

Gilmore shares the characteristically refined steel and glass envelope, rectilinear lines and structural clarity of many previous Busby + Associates projects. The station is designed for connection at mezzanine level to future commercial buildings, and from the street the main architectural feature is a glazed elevator tower. Gilmore’s tours de force however are its platform canopies, modular arrays of curved timberstrand panels that are remarkably simple, elegant and lightweight.

The canopy structure comprises a primary-system of back-to-back C-channel beams at five metre intervals along the platforms. These beams, which are separated by a spacer to accommodate roof drainage, span between HSS columns creating a series of moment frames. Resting on these frames are two rows of timberstrand panels, each panel measuring 2.4 metres by five metres. The curvature in each panel is maintained by a central four-legged king post connected to the panel corners by steel tension wires. The 38 mm panel thickness was the minimum required structurally, but coincidentally is also the minimum necessary to meet the code as heavy timber.

The timberstrand units were prefabricated off-site by Structurecraft, an independent company owned by the partners of Fast and Epp. Assembly was done with the panel upside down, the king posts being held in place simply by the tension in the two wires. The wires do not cross as one might first assume, but extend, via the kingpost, from one corner of the panel to the other corner on the same side. This ensures that the tension is equal in both wires and at the four corner brackets. The completed units are secured to the
moment frames by bolts that pass through light gauge steel channels on the ends of each panel.

The only discord in the final composition is the lighting and signage bulkhead which, because of the lightness of the canopy structure, appears heavy and intrusive.

While Gilmore Station will be at the heart of a new commercial district and surrounded by other buildings, Brentwood Town Centre Station has a uniquely prominent location, set nine metres above the median of Lougheed Highway, and visible from all sides. Accessible from below by a mezzanine landbridge that crosses the highway from nearby Brentwood Mall, the station’s striking double curved form hovers overhead like a spaceship.

The station structure is an intriguing combination of high and low tech. The double curved form could not be defined mathematically, so it had to be designed using three-dimensional Microstation software. This proved cost-effective because architects, engineers and contractors used the same 3D model for design, shop drawing and layout purposes. The model also permitted many design options to be compared at an early stage in the project, and optimal solutions were found. Although the glazing follows a double curve, the model made it possible to design a swiveling supporting clip that permitted 70% of the glazed area to be covered with a flat panel of standard size.

Above the glazing, however, the technology jumps back in time by a century or more, the glass giving way to a heavy timber roof built in the traditional way–using 38 x 89 mm lumber laid on edge and spiked together. The precision of the computer and the time-honoured pragmatism of site carpentry has proven an effective combination, and Brentwood is arguably the most striking station on the Millennium Line.

The main structural elements supporting the outer shell are a series of curved composite ribs set at five metre centres, the lower (wall) section consisting of steel, and the upper (roof) portion of glue-laminated timber. The timber portion is made up of 12 x 89 mm laminations, thin enough to achieve the required 3.8 m inside radius. These glulam ribs were all made using the same jig and have the same curvature on the lower face. The tapering profile of the roof in both plan and section is generated by cutting the ribs incrementally to nine different lengths, the longest in the centre of the platform, the shortest at the ends.

The ribs of the two canopies are connected via a structural gutter to steel cross-bracing and V-shaped steel struts that create a system of moment frames and transfer lateral loads across the central void. Again the complementary properties of steel and wood dictate the architectural language.

Just two stops from the end of the Millennium Line in New Westminster is Braid Street Station, designed by Architectura Architecture and Planning and Walter Francl Architect and engineered by C. Y. Loh Associates. Braid Station is prominently located at the crossroads of major transportation arteries serving the Fraser Valley. It has been designed as the anchor for a new civic space that will become the focus of a developing residential neighbourhood.

The immediate context comprises large-scale industrial buildings, including trucking and lumber operations–the latter playing an integral part in the local economy for more than a century. It is this historical and physical context that has inspired the building’s simple forms and robust palette of concrete, steel and glulam construction.

The building comprises two main volumes. At the lower level a large south-facing concourse recalls the grand scale of historic transportation buildings and is oriented towards the new civic square. Above it, and angled in plan, a single inclined shed roof shelters both the elevated platforms and the guideway. At this level, a fully glazed north -east wall affords spectacular views of the Coast Mountains.

Both the concourse and platform roofs consist of glulam beams and purlins supported on HSS columns, extending into dramatic cantilevered canopies of up to 3.6 metres. The beams extend beyond the eave line and are protected from the weather by a castellated flashing that gives the building a distinctive silhouette.

On the northeast (high) side of the platforms, the supporting structure is designed to minimize obstruction and maximize views, with pairs of 874 mm deep glulam beams supported on slender steel Y-columns. Lateral loads are transferred to the low side where each beam is individually supported on an HSS column. A triangulated knife-plate and strut hold the beam end away from the column in a strong and elegant connection that lends a human scale to the space.

When the Rapid Transit Project Office (RTPO) commissioned architects to bring quality and individuality to its new stations, it was in the belief that this would contribute positively to the success of the system. While it is too early to answer that larger question, RTPO certainly got what it hoped for architecturally. Individually, the stations have already been recognized in several provincial and national design awards programs. Collectively, the vitality and variety of these structures comprise an important primer in composite construction, and a welcome new direction in Canadian architecture.

Jim Taggart, a retired Vancouver architect, works as a freelance journalist and educator.

RENFREW AND RUPERT STATIONS

VIA Architecture (formerly Baker McGarva Hart Architects)

Client: Rapid Transit Project Office

Architect team: Graham McGarva, Catherine Hart, Eric Steadman, Greg Ball, Andrew Norrie (Rupert); Graham McGarva, Dale Rickard, Greg Ball, Charlene McCawley, Andrew Norrie (Renfrew)

Structural: Fast + Epp Partners

Mechanical: Keen Engineering

Electrical: Sandwell Engineering Inc.

Landscape: Durante-Kreuk

Public Art: Muse Atelier (Rupert); Atkinson Iconography Studio (Renfrew)

Area: 525 m2 (Rupert); 605 m2 (Renfrew)

Budget: $5.3 million (Rupert); $5.3 million (Renfrew)

Completion date: September 2002

Photography: Ed White

GILMORE AND BRENTWOOD STATIONS

Busby + Associates Architects

Client: Rapid Transit Project Office

Architect team: B. Billingsley, M. Bonaventura, P. Busby, S. Edwards, T. Mullock, M. Nielsen, R. Peck, A. Slawinski (Brentwood); B. Billingsley, P. Busby, P. Bodonarus, M. Bonaventura, S. Chevalier, T. Mullock, M. Nielsen, R. Peck, A. Slawinski (Gilmore)

Structural: Fast & Epp Partners

Mechanical: Klohn Crippen

Electrical: Agra Simons

Landscape: Durante Kreuk

Public Art: Jill Anholt (Brentwood); Muse Atelier (Gilmore)

Area: 2,100 m2 (Brentwood); 2,300 m2 (Gilmore)

Budget: $8.1 million (Brentwood); $7.9 million (Gilmore)

Completion: 2002 (Brentwood); 1999 (Gilmore)

Photography: Nic Lehoux

BRAID STREET SKYTRAIN STATION

Stantec Architecture (formerly Architectura) in association with Walter Francl Architect Inc.

Client: Rapid Transit Project Office

Architect team: Walter Francl, Peter Buchanan, David Harding, Neville Doyle, Brent North, Eric Pettit, Ken Tsai

Structural: C.Y. Loh & Associates

Mechanical/Electrical: Earth Tech Canada

Landscape: Phillips Farevaag Smallenberg

Public Art: Katherine Kerr

Area: 1,800 m2

Budget: $5.7 million

Completion: December 2001

Photography: Ed White

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