rom Montreal to Macau, stainless steel has proven to be a material of choice for the iconic structures that bridges represent. The projects outlined in an International Stainless Steel Forum report issued earlier this year range from small pedestrian bridges less than 100 meters long to those spanning 55 kilometers. We chose six of these to investigate.
Canada made the geometry of our design mandatory and the bridge stands exactly as intended. 
First commissioned in 1962, the Champlain bridge conveys 50 million vehicles a year, the highest traffic for a bridge in Canada. At peak hours, up to 6,200 vehicles cross it in a single direction. The 3.4-kilometer-long bridge has clearance sufficient over the St. Lawrence Seaway to allow the passage of ocean vessels to and from the Great Lakes.
The new bridge carries three separate transportation corridors, each supported by its own steel superstructure. Both north and south corridors have three-lane highways with inner and outer shoulders. The north corridor includes a 3.5-meter-wide lane for pedestrians and cyclists.
The deck and concrete on the old bridge were badly damaged by corrosion, caused mainly by deicing salts, while traffic grew greater than it was designed for. Maintenance expenses also rose substantially. The new bridge, opened in 2019, is built of reinforced concrete. The stainless rebar resists corrosion from deicing salts.
“In spite of an extreme time pressure, the design process was unusually smooth, so it was possible to complete the tender design in about seven months,” says Dissing+Weitling’s lead architect, Jensen. The design was developed in workshops in Montreal, then presented to and discussed with the client, Infrastructure Canada, and the Visual Quality Advisory Committee. “I am very happy that Canada decided to make the geometry of our design mandatory and that the bridge therefore stands exactly as intended.”
The 36-kilometer-long causeway was built on pilings bored into the seabed. The bridge, featuring an arch pylon, faces a marine environment and heavily populated area, so the designers sought to create a structure that could withstand the rigors of salt water and carbon dioxide emissions.
Designers sought to create a structure that could withstand the rigors of salt water and CO2 emissions. 
“Pedelta designed two pedestrian and cycle bridges using duplex stainless steel for the entirety of the structure—an unprecedented technical innovation in North America, providing a durable long-term asset with premium aesthetics for the community,” says CEO Juan Sobrino.
“The structure has an extended life cycle, is more corrosion-resistant and requires less maintenance, thus reducing its overall cost,” he says.
“Pedelta proposed a unique arch design consisting of a tied stainless-steel network arch, with a distinctive crossing diagonal hanger pattern, and a triangular profile, with a single arch rib inclined at 18 degrees to provide a slender, transparent and elegant structure,” Sobrino continues.
“Durability was especially important [as the bridge is] exposed to the use of deicing salts. Our team considered the life-cycle cost, which includes all anticipated maintenance costs,” he says. The design aimed to add a “sense of place and a distinctive visual element to the city without dominating the skyline of the neighborhood and the historic setting.”
The project was awarded by CreateTO, representing the City of Toronto. Dufferin Construction was the building contractor.
All the stainless steel rebar for the project was produced by Roldan S.A. in Spain.
“All three bridges were proposed to be cable-supported with central towers of different shapes placed between the carriageways to give both a visual affinity and variety between the bridges,” according to London-based Arup.
Environmental considerations dictated that single-column piers support the structure with piles buried in the seabed. “This minimizes obstruction to waterflow and impact on the habitat of Chinese white dolphins. Resilience and sustainability were high on the agenda to address concerns such as frequent typhoons and dolphin habitat.”
Further, the firm states, “The megastructures were built to last 120 years, in accordance with the design standards, capable of withstanding extreme events such as earthquakes and typhoons.”
The bridge is expected to receive heavy use from the more than 50 million people that live around the Pearl River Delta.
The designer and fabricator Stål & Rörmontage chose stainless to reduce the size and weight of the structure, which saves on material cost as well as on transportation and installation. The corrosion-resistant material promises low maintenance costs, and no paint or other coatings are needed.
“Specifying stainless steel rebar for the critical areas of a structure reduces lifetime cost as well as maintenance-related downtime,” says Stephen Jones, commercial manager for rebar product at Outokumpu.
Although the initial cost of a stainless bridge, compared with one made from carbon steel, is higher, “this bridge has a lifespan of 120 years, with no need for maintenance, so total life cycle cost will be much lower,” says Peter Månsson, quality manager for Stål & Rörmontage. With stainless, abrasive blasting and repainting—typical maintenance for a carbon steel bridge—can be replaced by simple cleaning, which requires very short traffic closures, if any.
Duplex steel releases very low amounts of metal ions to the environment, and bridges made from it do not require any environmentally hazardous coating, according to Outokumpu.
The bridge connects two production area of the headquarters of Trumpf Inc., which builds metalforming, metal cutting, welding and 3D printing machinery.
The bridge is a lightweight shell construction, made of 2-cm-thick, double-curved stainless sheet. The shell edge is reinforced by upstands that twist toward four base points to form triangular bearing points.
Holes corresponding to the flow of force were cut into the shell with Trumpf’s own laser cutting machines. The size and density of the apertures depend on the degree of support needed at each location. On the walking surface, 14,300 small holes were filled with glass plugs.
The bridge was welded together on site from several components and then lifted into position.
