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Designers are searching far and wide for聽inspiration that will influence the look and function of the Burnside Bridge replacement.

At a meeting of the Burnside Bridge community task force earlier this week, project leadership showed examples of bridge design from around the world. The South Park Bridge in Seattle, the Indian River Bridge in Florida and the London Tower Bridge in England were discussed as excellent examples of various bridge types.

Paddy Tillett, a principal at ZGF Architecture, and Steve Drahota, vice president at engineering giant HDR’s Portland office, led the discussion, which was held virtually.

One bridge seemed to hold particular allure for Drahota: The Dagu Bridge in Tianjin, China, which opened in 2004 with an asymmetrical tied-arch design from T.Y. Lin International.

Drahota called the Dagu 鈥渁n incredible bridge鈥� and said the design is 鈥渟omething that has possibility for this (Burnside) bridge.鈥�

Tillett and Drahota were quick to note that no decision has been made regarding the future Burnside Bridge’s design. Some aspects are becoming clear, however, including a three-span design. Designers are planning a west span of about 425 feet long, a movable main span of about 450 feet and an eastside span of about 650 feet in length that would bridge over interstates 5 and 84.

鈥淚n composition these three spans have to work together, yet are solving different types of engineering problems,鈥� Drahota said.

The bridge will be about 115 feet wide to allow for ample space for vehicles, bicycles and pedestrians. 鈥淏urnside is not a freeway, but it’s an active city street and the bridge will be part of it,鈥� Tillett said.

Multnomah County is moving forward with a replacement of the iconic 1926 bridge, which officials say is at risk of destruction during a strong earthquake. In October, county commissioners selected a 鈥渓ong-span鈥� replacement option, citing its seismic resilience, lower cost of about $850 million and quicker construction timeline of about five years.

Tillett said the bridge has an architectural frame in downtown Portland that will influence the design. 鈥淪omething that resembles a freeway ramp won’t do; it’s in the middle of a city,鈥� he said.

A replacement Burnside Bridge is unlikely to resemble the existing span because of seismic concerns. Like the new Sellwood and Tilikum Crossing bridges, a replacement Burnside is expected to remain usable by emergency vehicles in the aftermath of a devastating Cascadia subduction zone quake.

Designers face a conundrum: The thinner the bridge deck is made, the stronger a support structure must be built atop the bridge, whether that’s cable stays, tied arches or another design scheme. The Harbor Bridge in Barcelona, for example, has tension ties that enable a thinner bridge deck but block certain views, Drahota said.

Certain bridge types have already been all but dismissed as unworkable in the Willamette River. A swing bridge, for one, would be costly, slow and require the entire river channel to be cleared of traffic, Drahota said. Diagonal, sail-shaped split spans also may not work for the Burnside’s length, he said.

The bridge must make space for neighboring buildings and allow for ships to pass underneath.

The project will be paid for by a mix of federal, state and local funding. Last year, county commissioners voted to nearly triple vehicle license fees to help pay for the new bridge.

The community task force will meet again on Dec. 7 and Dec. 21. The next landmark for the project will come when a draft environmental impact statement is released. That document is expected to arrive in January or February.