Duplex stainless steels have evolved significantly over the decades. The intricacies of their structure depend on the application; however, the range of applications has increased due to a better understanding of metallurgy and refining methods so that duplex steels are better able to withstand more extreme environments.
Multiple projects around the world showcase duplex stainless steel’s intriguing qualities. Some serve as pragmatic modes of pedestrian movement cloistered by protective yet stunning mastery. Some are historical commemorations that freeze a moment in time. Others are works of art hiding in plain sight.
By Kristen Charles, Editor – Stainless Steel World Americas
Harbor Drive Pedestrian Bridge – San Diego, California, USA
The Harbor Drive Pedestrian Bridge is a landmark that fulfilled the 100-year aspiration to link Balboa Park with San Diego Bay. It was constructed using duplex stainless steel, selected for its strength and superior corrosion resistance, qualities that are essential for a bridge in a marine environment that is regularly exposed to salt fog but receives limited precipitation. The bridge is 550 feet (168 meters) long and provides pedestrians with a new access point to downtown San Diego.
Stainless steel hand railings, aircraft cable mesh, and specially designed concrete finishes and walking surfaces characterize the pedestrian bridge’s transparent profile.
Skidmore, is licensed under CC BY-SA 4.0.
A spectacular 131-foot (40-meter) pylon inclines at a 60-degree angle over one side of the 20-foot (six-meter) wide deck, supporting the bridge’s pair of suspension cables. The deck is buttressed by 34 suspenders that are connected to the bridge’s main cable, which is shielded in a stainless steel welded pipe.
The 550-foot (168-meter) long self-anchored, suspension bridge was designed by Safdie Rabines Architects, and T.Y. Lin International served as the project’s structural engineers. It is one of the most unique bridges of its kind in the world and reflects T.Y. Lin’s vision of uncomplicated and sleek lines. Completed in 2011, the bridge’s dramatic features include indirect lighting and a curved deck. Pedestrians can admire the 360-degree, unobstructed views of San Diego from the bridge while conversely becoming part of the view for those appreciating the bridge from a distance.
Venus Rising – Brisbane, Australia
Venus Rising is the 76-foot (23-meter) high sculpture situated in Kangaroo Point Park overlooking Brisbane River. Completed in 2012 and designed by renowned British artist Wolfgang Buttress, the sculpture’s primary configuration comprises 10,790 individual welds and seven kilometers of 316 grade and 2205 duplex stainless steel tube, pipe and round bar that was furnished through Australian Stainless Steel Development Association (ASSDA)-sponsored Sandvik.
Queensland, by Kgbo, is licensed under CC BY-SA 4.0.
The cladding tube size starts at 0.5 inches (12 millimeters) at the bottom with 0.3 inches (8 millimeters) to 0.4 inches (10 millimeters) of tube in the middle, ascending to between 0.2 inches (6 millimeters) and 0.3 inches (8 millimeters) of solid round bar at the pinnacle. Tubes were supplied in 20-foot (6-meter) lengths and welded in place to create continuous lines of tubing that span its length. Venus Rising’s golden hue was achieved by heat treating the 0.5-inch (12 millimeter) thick stainless steel tubes, which run halfway up the sculpture. Buttress selected the golden color by baking different length tubes of varying thickness at temperatures ranging from 100 °C to 300 °C to compare the different shades.
Venus Rising exemplifies stainless steel’s hardiness and flexibility. Steel’s diverse finishing possibilities—heat treatment, polishing, or glass blasting—are embodied in the sculpture’s enduring aesthetic qualities.
ASSDA member and Accredited Fabricator D&R Stainless assumed fabrication of the 11 ½-tonne sculpture after the initial fabrication in the United Kingdom. Assembly spanned six weeks and followed Buttress’s concepts, illustrations, and 3D models. Visitors standing beneath the sculpture can peer past the intricate hollow Fibonacci and nautilus shell spiral and latticed and laddered construction into the sky through the aperture at the top of the sculpture.
Venus Rising’s lace-resembling design was achieved by laser cutting stainless steel rings from LDX 2101 and welding them to the sculpture. The rings varied in thickness from 0.8 inches (20 millimeters) down to 0.1 inches (3 millimeters). Bead blasting was applied to create the smooth, consistent finish. The structural integrity was verified using di-penetration testing on the welding used on the sculpture’s body. TIG and MIG welding processes were applied, and solid wire and flux cord were employed in the MIG welding process.
Garrison Crossing – Toronto, Ontario, Canada
Garrison Crossing is the first bridge in North America that is constructed entirely with duplex stainless steel. It was designed by engineering consultancy firm Pedelta and consists of a pair of bridges built to accommodate pedestrians and cyclists. Each arch rib slants at 18° and supports each bridges sleek flow.
Pedelta presented the idea of constructing the project out of duplex stainless steel due to its durability, long life span, high degree of corrosion resistance, and minimal maintenance, amounting to cost savings over the long term. The bridges were completed in October 2019 by Dufferin Construction.
CC BY-SA 4.0.
The bridges cross two railway corridors and serve as a physical and ideological connection between Stanley Park and Fort York by uniting communities and rejuvenating Toronto’s waterfront. Their two tied stainless-steel arches traverse the rail corridors to reduce crossing distance. The North Bridge spans 52 meters, while the South Bridge spans 44.5 meters.
Dublin Spire – Dublin, Ireland
Dublin Spire is visible from all over the city. The O’Connell Street Monument, the spire’s official name, was completed in January 2003 by Ian Ritchie Architects from London and Arup, the Project’s structural engineers. The result was a commanding spire overlooking Dublin.
The base of the 394-foot (120-meter) high spire has a ten-foot (three-meter) diameter and narrows to a six-inch (152-millimeter) diameter at its apex. The hollow silver spire landmark was constructed with Type 316 stainless steel.
The spire’s wall thickness at the base is 1.4 inches (36 millimeters) and 0.4 inches (10 millimeters) at the top. It shines by day and sparkles by night with light that reflects through 11,884 0.6-inch (15 millimeters) apertures in the top 39 feet (12 meters).
As Dublin is a coastal city exposed to salty air, incorporating Type 316 stainless steel was essential due to its corrosion-resistant properties. In addition, its smooth finish curtails dirt deposits. Shot peening was also applied to slightly enhance the light reflecting from the monument.
The project required 126 tonnes of Type 316 stainless steel (or approximately 2.5 tonnes of molybdenum). The monument was constructed with eight stainless steel hollow tubes. In addition, Arup designed a tuned mass damper to absorb vibrations and reduce sway.
Architect Ian Ritchie explained the polished pattern at the spire’s base is meant to evoke images of “mirrored seas or lakes or, conversely, as hundreds of islands floating in a mirrored sea.”
Helix Bridge – Singapore
The enigmatic Helix Bridge is a pedestrian crossing that was completed in 2010. It traverses Marina Centre to Marina South in the Marina Bay region of Singapore.
Design firm COX Group Pte. from Australia, Architects 61 from Singapore, and engineering firm Arup wanted to create a lightweight structure that protected pedestrians from the hot tropical sun and abundant rainfalls. The double helix configuration is a powerful aesthetic serving as a rigid truss that can sustain the bridge’s design loads.
The bridge was constructed using 1,000 tonnes of carbon steel and 650 tonnes of duplex stainless steel. Most of the bridge, including the helices and support structures, was constructed using grade 1.4462 (S31803); its corrosion-resistant properties are integral to combatting Singapore’s salty sea environment.
The required duplex stainless steel quantity, preliminary construction, and subsequent maintenance costs were a more cost-effective option than the required quantity and costs for a carbon steel bridge.
The bay-side viewing decks were constructed using grade 1.4462. The decks, which can accommodate approximately 100 people, enhance the pedestrian experience. Fabrication began with the delivery of steel from a European supplier to a workshop in Johor, Malaysia.
The 36-foot (11-meter) components were assembled as a test prior to their transport. A temporary steel bridge was constructed as a platform to build the permanent structure. The bridge has a height clearance of almost 30 feet (nine meters) and is 935 feet (285 meters) long.
National Salt Satyagraha Memorial – Gujarat Province, India
Satyagraha means “upholding the truth.” The National Salt Satyagraha Memorial in India’s Gujarat province commemorates the 24-day Dandi March led by Mahatma Ghandi in 1930 to protest Britain’s monopoly on the salt trade in India.
CC BY-SA 4.0.
The site was inaugurated in January 2019 and lies at the end of a route that symbolizes the march. The memorial comprises two 130-foot (40-meter) high stainless steel “arms” upholding a 2 ½-tonne glass cube that represents a “salt crystal”.
To endure the coastal region’s salty offshore winds, the structure was built with molybdenum stainless steel. The memorial park also contains 24 bas-relief murals each representing one day of the march, 80 life-sized sculptures depicting the marchers, and 41 Type 316 stainless steel solar trees that supply energy to the park.
The sculpture’s main frame is constructed of 2205 duplex stainless steel that is nine inches (220 millimeters) in diameter and laser-cut plates of varying thickness, ranging from 0.5 inches (12 millimeters) to one-inch (25 millimeters) of the same duplex stainless steel.
Over 50 tonnes of duplex were used to complete the structure. The steel contains 3% molybdenum to provide optimal corrosion resistance. The monument’s construction is symbolic of India’s strength during that juncture in the country’s history.
Conclusion
Every day, we pass stunning duplex stainless steel projects with superficial appreciation since few people realize the bridge they are crossing or the monument they are admiring was constructed with a steel that provides safety without extensive maintenance, corrosion-resistant properties, and relentless strength. Few comprehend the complexity in choosing the proper grade or the engineering required for the project to maintain its visual appeal and long-lasting security.
Despite the proclamations about the benefits of duplex stainless steel, it does have disadvantages. Its high strength can offer less ductility and limited ability to flex without fracturing or causing severe thinning. Its machining capabilities like milling, drilling and turning are also limited. However, these obstacles simply mean that more research and development, and advancements will continue.
References
- https://bssa.org.uk/bssa_articles/2-duplex-stainless-steels-a-simplified-guide-2/
- https://nickelinstitute.org/media/2870/case-study-helix-pedestrian-bridge.pdf
- https://www.pedelta.com/garrison-crossing-pedestrian-and-cycle-bridges-p-11-en#:~:text=Project%20Description,Design/Construction%20Approach
- https://www.tylin.com/work/projects/harbor-drive-pedestrian-bridge
- https://www.outokumpu.com/en/expertis/2016/beauty-that-carries-the-load
- https://www.assda.asn.au/blog/254-astainless-icon-for-brisbanes-skyline
- https://www.wolfgangbuttress.com/venus-rising-project-detail
- https://www.imoa.info/molybdenum-uses/molybdenum-grade-stainless-steels/architecture/stainless-steelspire-graces.php
- https://www.imoa.info/download_files/molyreview/excerpts/23-2/Salt_memorial.pdf
- https://publicart.ie/main/directory/directory/view/the-spire-of-dublin/38a5a1c-7cc360e43ee936d8048b9be44/#:~:text=The%20monument%20was%20designed%20by,was%20completed%20in%20January%202003.