Movable Bridges - Spokane Street Swing Bridge (2)

Another view of the Spokane Street Bridge. Note the old bascule railroad bridge in the background. This area is part of a huge port. The Spokane Bridge carries container trucks into the harbor while also allowing container ships through the channel.


The previous bridge restricted access to the channel and so it was replaced with a double leaf swing bridge that can rotate completely out of the way. Each leaf is 450 ft from end to end and the bridge  provides about 350 ft  of channel clearance.


The tower that controls the bridge can be seen on the right side of the photo. Each leaf rests on a 103 inch diameter steel piston. To move the bridge the operator disengages locks that hold the two leafs in place, turns on a pump that raises the two pistons on hydraulic fluid, and then activates two arms that turn the leaves in opposite directions. That was the case until after the 2001 earthquake when one piston was found to be damaged. The City of Seattle had more pistons sitting on the site and replaced the damaged cylinder in a few days. Eventually KPFF, who acted as a sub-consultant to URS, designed a new cylinder that was less likely to suffer fatigue.


A concrete swing bridge is an innovative idea and this attractive bridge won a number of awards.

Movable Bridges - Spokane Street Bridge (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Movable Bridges - Spokane Street Swing Bridge

This is our second look at these bridges (first shown in my May 20, 2009 blog). This is a more detailed examination of the lower, double leaf swing bridge that crosses the Duwamish River and carries traffic between Harbor Island and West Seattle.

I find it strange that the two leafs can swing past each other without touching. The two (7500 ton) leafs are supported on hydraulic cylinders that lift them up an inch and then swing them out of the way. The operation is performed eight times a day and takes ten minutes.

I'm standing in the control tower where a bridge operator moves the bridge. I was there to inspect bridge damage after the 2001 Nisqually earthquake. However, it was never clear whether one of the cylinders became damaged from the earthquake or because of the strain of lifting such a heavy structure. The bridge was quickly repaired and put back in service. We'll take another look at this structure tomorrow.

Movable Bridges - Spokane Street Swing Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Washington State Bridges: Aurora Bridge (2)

Before the building of the Aurora Bridge, traffic had to wait for the raising and lowering of one of the many bascule bridges that crossed the Lake Washington Ship Canal.  With the construction of the Pacific Highway (State Route 99), pressure mounted to build a bridge that didn't need to be opened and closed for ship traffic. The Aurora Bridge was the city's answer to that problem. It was also the first major highway bridge in Seattle built without streetcar tracks.

The 800 ft long deck arch is composed of two 325 ft long cantilever arms and a 150 ft long dropped-in Warren truss.

Washington State Bridges: Aurora Bridge (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Washington State Bridges: Aurora Bridge

From the last few day's photos, Seattle looks like it has many large bodies of water and many large bridges. At least it looked that way to me during my two visits to Seattle.

The Aurora Bridge (also called the George Washington Memorial Bridge) crosses the Ship Canal just west of Lake Union. The double-deck Ship Canal Bridge (from Tuesday's blog) is just east of Lake Union.  The canal carries ships from Puget Sound to Lake Washington. Consequently, both bridges provide vertical clearance to all but the tallest masted schooners.

I would call the Aurora Bridge a truss arch, although it could also be called a cantilever bridge.  It was completed in 1932 and was the tallest bridge (with 167 ft vertical clearance) in Seattle for many years. It is 2,945 ft long with a 475 ft long arch span and a 70 ft width.  Seattle has a lot of traffic with many commuters and this bridge carries over 71,000 vehicles every day.

Washington State Bridges: Aurora Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Washington State Bridges: West Seattle Bridges

The high level West Seattle Bridge stands 140 ft above the Duwamish River at Elliott Bay in Seattle. It is a cast-in-place, segmentally constructed, prestressed concrete bridge. This means the bridge was built as two balanced cantilevers, with the formwork being pushed out from each end, until it met in the middle. The superstructure is two box girders and the substructure is two column bents. It was completed in 1984, after a freighter rammed into the previous bascule bridge at this site. The low-level West Seattle Swing Bridge, constructed at about the same time, is immediately north of the bridge and carries Spokane Street traffic over the Bay. These two bridges, one wide and high and the other swinging out the way, provide plenty of room for ships moving in and out of the Duwamish River.

Washington State Bridges: West Seattle Bridges by Mark Yashinsky is licensed under a Creative Commons Attribution 3.0 United States License.

Washington State Bridges: Ship Canal Bridge

We'll spend the next few days looking at bridges in the Seattle Area.

The Ship Canal Bridge carries I-5 over Portage Bay in northern Seattle. It was completed in 1961, a year before the opening of I-5. It is a 4429 ft long bridge that includes a six span (2294 ft long) double deck truss structure over the water. The top deck is 82 ft wide and carries eight lanes of two-way traffic. The bottom deck has four lanes that carry southbound traffic in the morning and northbound traffic in the afternoon. At almost 200' tall, it is a very impresive structure.

Washington State Bridges: Ship Canal Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License.