Ballard Bridge seen from Fishermen's Terminal.
Is the Ballard Bridge ‘functionally obsolete’?
In view of the Skagit River Bridge collapse last May, the Ballard News-Tribune decided to investigate the condition of the Ballard Bridge.
The iconic bridge was built in 1917 and has a length of 2,854 feet, linking Magnolia and Queen Anne with Ballard. It is one of the longest bridges in Seattle. Moreover, it is one of five bridges on the ship canal that boats have to pass under from Lake Washington to Puget Sound.
The bridge has undergone many changes. It was originally constructed with wood but has been remade through its almost 100 years with concrete and steel. Steel approaches were constructed 1937 and concrete was added at the far ends of the bridge in 1937 and 1957.
In all its forms the bridge has been designed with the regulations set by the Federal
Highway Administration. Using measures set by these Federal regulations, SDOT released a report in 2012 that examined the quality of all the bridges in Seattle, and there were findings that at first seem alarming.
The FHWA measures are based on the foundation, superstructure and deck. FHWA uses these measures to determine the sufficiency rating for bridges on a national level. There are also contextual elements that determine the sufficiency rating such as transportation demands of the bridge within a given community. For example, traffic levels change a bridge's rating. The rating is from one to 100.
John Buswell, Manager of Roadway Structures with SDOT, said rarely do bridges get a 100 rating because the bridge being measured would need to be brand new, and the functionality within a given community brings the rating down.
For the Ballard Bridge, Buswell said SDOT looks at it as three separate bridges, including the bascule, steel approaches and concrete piers.
In the 2012 report the sufficiency ratings measured the bascule at 51.21, the steel
approaches at 35.25 and the concrete piers at 48.45.
Buswell said that these numbers are on the low end of an average, especially with the steel approaches. There are some factors that bring down the score such as the lane width. Bridges today have 12-foot lane widths but the Ballard Bridge is much less than that and so its overall sufficiency rating is lowered.
Moreover, the Ballard Bridge is considered by the FHWA as “functionally obsolete,” which is a term used by engineers with the FHWA that is misleading to people outside the profession. Buswell said that the term more accurately means that if the bridge were built today it would be built to current code and the term does not imply that the bridge is unsafe or not functioning correctly.
“We spend a lot of time trying to put these measures into terminology for the average person. FHWA does not mean current standards. It means if we built it today we would build it differently with lanes, rails and weight capacity up to standard. However the weight capacity of the Ballard Bridge would be only a little higher because it originally was built to have street cars and to handle higher weights,” said Buswell.
So if the bridge is functionally sound, at the base, safety comes down to maintenance.
Buswell explained that an SDOT bridge teams does a thorough examination of the bridge every year to make sure its safe. He said the biggest issue they face is seawater spray in the air from the Sound getting on the steel. To protect the steel from corrosion, it undergoes surface painting as needed. Another issue is moisture in the concrete that can undermine its structural integrity.
In an earthquake zone with some experts anticipating another big quake soon, “structural integrity” of a bridge becomes a very important thing. That’s why SDOT has been making seismic retrofitting changes to the bridge since the 90’s.
Buswell said that there have been two phases of the seismic reinforcement so far and that the second is almost complete. Reinforcement of the concrete piers and replacing rivets throughout the bridge has occurred, however Buswell said there remains work to do on the bascule. That work in contingent on transportation funding.
“The bridge is safe and undergoes our highest management rating,” said Buswell.