Friday, March 5, 2021

Is This the Look of a New Burnside Bridge?

Two conceptual views of an "unbalanced" Burnside Bridge show the cable supported option, above, and the tied arch. (HDR)

 Unbalanced. Asymmetrical.  Funky?

An advisory discussion by members of the Portland Design Commission and the Historical Landmarks Commission suggests that a new Burnside Bridge should be divided into three parts, and look unlike any other bridge spanning the Willamette River.

The 650 feet at the east end likely will be supported by two towers with cable supports or a tied arch.    The center of the bridge would have a bascule mechanisms based within two piers extending deep into the river bed.  The western portion of the bridge would consist of a truss structure positioned under the surface deck, thus keeping views unobstructed for west-bound travelers heading into the Skidmore-Old Town Historic District.

Members of the two commissions reached a tentative consensus on a three-part bridge based on unstable soils on the east side and the disparate urban environments on the river’s two sides.

“You are entering two different worlds,” said Don Vallaster, an architect on the design commission.  While the west side has a largely 19th Century feel with its old historic buildings, the east side has become modern, angular, tall and glassy. 

 “This is an asymmetrical context,” said Andrew Smith, an architect on the landmarks commission.  “It almost seems like an asymmetrical design is needed.”

 Brian McCarter, a landscape architect on the design commission, said bridges typically are designed to be balanced, rising to a structural peak at the center.  But here, the geography and the presence of railroad tracks and the freeway on the east side mitigate against a single balanced structure.  “It’s a real struggle to make a single beautiful composition out of the whole thing.”

 A similar “unbalanced” design could be accomplished with a tied arch at the east end, looking like a smaller version of the Fremont Bridge.  Members of the two commissions said they preferred the cable supported concept, where the two towers would be landmarks signaling entry to the east side.

The Burnside Bridge was identified by regional officials in 1996 as the primary emergency route connecting 19 miles of city streets in case of a major earthquake.  Several other bridges are expected to suffer serious damage or route obstructions in a magnitude-9 quake.  The existing Burnside Bridge is expected to collapse at that magnitude.

 “I love this bridge,” Drahota said of the current Burnside. “We tried our hardest to keep it.”  But he said studies showed too many problems for a retrofit to work.

Yet for bridge designers, the bridge needs to be more than a passage for vehicles, bicycles and pedestrians.  They want it to represent the heart of Portland and the vital dividing line among four city quadrants.  And they would be pleased if it can be attractive enough to draw favorable attention as a landmark and even be a draw for tourists. 

 All designs showed at the March 4 hearing were conceptual in nature rather than detailed.  Steve Drahota, technical leader for the HDR consulting team, said he would bring three-dimensional renderings to a future meeting.

 Julie Livingston, the design commission chair, said the three dimensional studies would give the panels a better view of bridge views from all angles.  Drahota said public comments on the conceptual drawings so far are heavily split between the cable supported approach and the tied arch.  A final bridge design is supposed to be made by City of Portland and Multnomah County officials in the coming summer.

  A funding package has yet to be identified for the project.  In theory, the new bridge is to be finished by the end of this decade.


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