Portland's Bridges: Marquam Bridge

The Marquam Bridge is a double deck cantilever truss bridge that carries I-5 over the Willamette River. The main span is 440 ft long, the side spans are 301 ft long, and the deck is 57 ft wide. It carries four northbound lanes on the top deck and four southbound lanes on the bottom deck and provides 130 ft of vertical clearance over the river. The bridge was designed by the Oregon Dept. of Transportation (ODOT), the piers were built by Kiewit, and the superstructure was built by US Steel. It was opened in 1966 at a cost of $11 million.

This truss structure is connected to steel girder ramps including the beginning of one on the east side to connect to the Mount Hood Freeway, which was never built. The bridge was designed economically with little public input and it's considered to be an eyesore. I think it's a perfectly normal looking three span truss bridge, but for some reason it upsets Portland sensibilities. Perhaps it's because it carries 136,000 vehicles a day into and out of the city. In any event, there are committees that come up with various schemes for removing this bridge that are never acted upon.

Portland's Bridges: Marquam Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Arch Bridges: Fremont Bridge

The Fremont Bridge carries US-30 and I-405 traffic over the Williamette River in downtown Portland, Oregon. It was named after the military officer, explorer, and presidential candidate John Charles Fremont.

The bridge looks like a through arch but it is actually a tied arch, with the 902 ft (275 m) center section fabricated in California, assembled at Swan Island, floated to the bridge site, and lifted 175 ft (53 m) into place.

It is a double-deck bridge with four lanes of traffic in each direction. A commission was invited to participate in the design, which greatly increased it's cost (to $82 million). The bridge was opened to the public in 1973. At that time, it was the world's longest tied arch bridge ever built and the largest weight (at 6000 US tons) ever lifted.

A tied arch bridge is sometimes called a bowstring arch because the arch is like a bent bow with bowstring (the deck and girders) under tension. These high stresses make this type of bridge susceptible to maintenance problems due to fatigue at the connections.

Arch Bridges: Fremont Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution 3.0 United States License.