In 2011 the city of San Diego unveiled the iconic Harbor Drive Pedestrian Bridge, a critical link between the city’s historic Balboa Park and the picturesque San Diego Bay. Because of its close proximity to San Diego Bay’s marine environment, the bridge was constructed using stainless steel (2205 duplex from producer Outokumpu) instead of traditional painted carbon steel. The landmark bridge is only the second major pedestrian bridge in the U.S. to feature stainless steel as a structural component.
Engineers from T.Y. Lin International, the project’s design firm, were faced with the challenge of material selection that would address both structural and aesthetic concerns for the project.
“We wanted something with a high-quality finish, because pedestrians would be interacting with the bridge at a much slower pace than one would passing under in a vehicle,” explained Dan Fitzwilliam, senior bridge engineer at T.Y. Lin. “Because the bridge is close to the San Diego Bay, we were searching for a 100-plus-year service life, so a high resistance to corrosion was required. Typically a lot of stainless steel is used in bridge handrails and architectural elements. But in this case, the stainless steel had a load-carrying capacity, too, so the stainless had to have a high strength. Duplex made the most sense, and we settled on 2205 because of its high corrosion resistance and high strength.”
The Harbor Drive Pedestrian Bridge has a 354-ft-long main span and is a single-cable, self-anchored suspension bridge that spans six railroad tracks and several lanes of vehicle traffic. The bridge features a 131-ft-tall concrete pylon and curved deck that is suspended along just one side. The pylon is inclined at a 60-degree angle from vertical, reaching over the deck and supporting the main cable. Thirty-four individual suspenders, attached to the main cable, support the 20-ft-wide deck. This main cable is carried in a 2205 duplex stainless steel pipe fabricated out of plate from the producer, Outokumpu, to support the bridge deck via tension cables through the pipe and the heavy plate railing posts.
T.Y. Lin more often works with concrete as the structural component of its bridge projects. Fitzwilliam confirmed, “We weren’t aware of 2205 previously. When we started to list the criteria for the San Diego bridge, we contacted TMR Consulting [a metallurgy consulting firm for Outokumpu] to aide us in the search. They were instrumental in the final material selection.”
The material was then sourced out to a service center.
“This was a design-bid-build job, so we put 2205 in the specs and the contractor found their own suppliers of the materials,” noted Fitzwilliam. 2205 plate for the project was produced by Outokumpu’s New Castle, Ind., mill. Fabrication for the bridge was performed by AMECO, in Cleveland, Ohio. Some cable hangers with stainless steel parts were manufactured overseas in Germany by Pfeifer also using 2205.
Photos by Brooke Duthie.