Terri Meyer Boake BES BArch MArch LEED AP
Associate Professor :: Associate Director :: School of Architecture :: University of Waterloo

Humber River Pedestrian Bridge

Montgomery Sisam Architects

Toronto, Ontario

Project Information:

(text taken from Advantage Steel, Issue No. 6, December 1996)

Much admired for its attractive design, the Humber River Pedestrian Bridge is a sparkling new addition to Toronto's waterfront. Casual observers of the bridge – awed by its soaring tubular arches and intricate cross-bracing motif – are likely to overlook the structural innovations that made it all possible.

Unique configuration

Located at the mouth of the Humber River, the 139-metre pedestrian-bicycle bridge connects several trails along a scenic waterfront park. The project is the first step in a multi-year plan by Metro Toronto Transportation to replace a series of existing structures. With architectural expression and engineering design joining forces to achieve its unique configuration, the new bridge was built using 1200 mm diameter high strength steel pipe bent into twin arches rising 21.3 m above grade. The spacing between the arches is wide at the base but narrow at the top, imparting a futurist basket-handle appearance to the superstructure. A total of 44 stainless steel hangers of 50 mm diameter were strung from the arches to support the 22 floor beams forming the bridge deck, creating what architect Peter Sisam calls a "room-like quality" for visitors crossing the bridge.

The bridge was designed in accordance with the 1993 Ontario Highway Bridge Design Code. Due to the low bearing capacity of the soil, a tied-arch concept was adopted with the horizontal arch thrusts carried by high-strength steel cables within the deck. The bridge abutments rest on five concrete-filled caissons socketed into the bedrock 30 m below grade.

The tapered shape of the floor beams was dictated by both structural and architectural reasons. According to structural engineer Ken Price, "The floor beams are simple spans in the transverse direction, suspended at each end by a single hanger. These beams are efficient in bending when tapered to the hanger sup-ports. In addition, they required sufficient depth to accommodate the primary post-tensioning contained in the central deck spine. The rounded ends and non-prismatic shape were otherwise de-tailed for aesthetic reasons."

Delcan structural engineers designed the entire bridge with the assistance of the finite element program SAP 90, while Rowan Williams Davies & Irwin of Guelph, Ontario, carried out an independent assessment of the bridge aerodynamics.

Innovative construction

McCabe Steel fabricated the tubular structure using gas-fired ovens to heat the steel pipe sections. Bending operations involved a system of saddles, supports and weights devised to achieve the pro-per curvature. Tight tolerances on the parabolic arch geometry (out-of-round and camber) required careful consideration of the chemical and physical material changes due to heat bending. A pre-assembly of the pipe sections end-to-end in the fabricator's shop provided the necessary dimensional verification.

The bridge was completely erected on land and launched over the Humber River by Dominion Bridge, Inc. Arriving at the site in separate pieces, the steel arches were welded together on the river bank and equipped with cross-bracing, hangers and cross-beams. "The alignment of the sections, which had to be accurate within mm, would have been very difficult if not impossible if it had been done in the air over water. By assembling the complete bridge on land, half the individual arches could be pre-assembled and welded flat on the ground with easy dimensional control," explains Brian Thompson of Dominion Bridge. Temporary cables were added to tie the ends of the structure together, and the complete 40'' assembly was erected in one piece.

The launching operation began with the leading end of the bridge placed on a floating barge and pulled across the river by winches and cables while travelling cranes supported the trailing end. Lifting gantries at both ends of the 300-tonne arches then took over the erection sequence as anchor plates fitted to the bases were fastened onto receiving thrust blocks. The concrete deck and stainless steel railings were installed after the bridge was erected.

Corrosion protection

The different types of structural components and their exposure to the elements called for special corrosion protection measures. For the arches and floor beams, the standard three-coat protection system recommended by the Ministry of Transportation of Ontario was used. Stainless steel was specified for the hangers and railing system primarily for architectural and maintenance reasons. To avoid a premature corrosion failure arising from galvanic action, the stainless steel hangers were isolated from the mild steel hanger hardware by means of a sacrificial zinc coating, waterproofing and fabreeka pads.

The natural environment presented numerous challenges to designers who also had to contend with interest groups and government regulations. Planners considered the environmental impact of the bridge, river navigation, protection from Lake Ontario storms and erosion, public safety and problems related to the soft organic soil along the river bank.

Historic site

The double-arched bridge forms a gateway between Toronto and Etobicoke along an aboriginal trading route linking Lake Ontario to the north. Emphasizing the cultural history of the site, native imagery was skillfully woven into the design of the bridge. The steel cross-bracing between the arches exhibits an elegant cutout pattern suggesting a repeating Thunderbird motif, an important symbol for the Eastern Woodland First Peoples who inhabited the site for centuries. Additional cultural elements are evoked by the bridge abutments with their decorative panels depicting turtles, canoes, and other native icons.

Recipient of the 1995 Ontario Steel Design Award from the Ontario Region of the CISC and recognized as a local landmark, the Humber River Pedestrian Bridge proves once again that structural steel can be as beautiful as it is functional.

Architect: Montgomery and Sisam Architects,Toronto
Structural Engineer: Delcan Corporation, North York
Artwork: Environmental Art works Studio, Toronto
Owner: The Municipality of Metropolitan Toronto Transportation Department, Toronto
General Contractor: Sonterlan Construction Corporation, Richmond Hill
Steel Fabricator: McCabe Steel, Stoney Creek
Steel Erector: Dominion Bridge, Inc., Oakville

Project Images:

View looking west along bridge.
View up to the support system for the bridge

Plates were welded to the large tubular members to which are attached the suspension rods.
Closer view of a single plate and rod attachment.

A stainless steel railing system provides protection for the pedestrians. Here you can see the horizontal projecting steel members that support the deck.
View looking east along the bridge.
Overall view of the bridge.
The large HSS tubular support members are bolted to concrete abutments.
View down towards the tube to concrete foundation.
Detailed view of the railing.
View straight up into the centremost section of the bridge "truss", which is devoid of bracing.
Detail of rod to plate connection.
View of the top support system.
Ta - dah.

back to steel gallery
back to main gallery

These images are for educational use only and may not be reproduced commercially without written permission. tboake@sympatico.ca

Updated September 25, 2005


September 25, 2005