Fox Island bridge analysis
First and foremost, the bridge is structurally safe to drive on, and it’s safe for trucks that obey the posted limits on the bridge. Overweight trucks have requested permission from the County to traverse our bridge – and some of those have been denied. So the truck companies do feel compelled to comply – probably due to the very high consequence if they don’t and get caught or create a problem.
The deterioration that was highlighted in the media was on the concrete foundation blocks that support the bridge. Those blocks (the size of your living room, or larger) are spalling chips off the edges, reducing the footprint of the block. However, the blocks were built bigger than the design and the spalling has not even gotten to the original design dimension for most of the footings. Some defects do penetrate into the area of the “as-designed” foundation face. The seismic analysis was completed in the 1990’s, and the superstructure retrofit was completed in 2003. There has been no seismic retrofit to the substructure, ie that portion of the bridge located below the girders. There is no retrofit planned for the substructure. The expense for a seismic retrofit to the substructure would likely approach, if not exceed, the cost to build a new bridge – and we would still have a 60 year-old bridge with its many design deficiencies.
Speaking of deficiencies, what is the cause for the rating of 7 out of 100? The sufficiency rating is based on a scale between 0-100. The rating is used only for a basis for establishing eligibility and priority for replacement or rehabilitation of bridges with Federal Highway Bridge Replacement and Rehabilitation Program funds. The sufficiency rating is not used as a measure of structural integrity or safety. A bridge with a sufficiency rating of less than 50 and classified as structurally deficient or functionally obsolete is eligible for replacement funds using Federal Highway Bridge Replacement and Rehabilitation Program funds. The sufficiency rating is a result of a variety of structural and non-structural data. In a nut shell, the sufficiency rating for the Fox Island bridge is a 7.33 as a result of a number of these factors. Among the factors are:
-Structural adequacy relating to the design of the bridge as compared to current design standards (the bridge does not meet current design standards for many of its elements: roadway width, pedestrian safety, bicycle safety, and, earthquake design).
-Structural condition of the superstructure and substructure (showing signs of deterioration).
-Geometry of the structure such as curb to curb width, approach roadway width and alignment of the approach roadway.
– Number of lanes on the bridge.
-ADT, (average daily traffic count) which is over 6,000 for our bridge.
And, the bridge gets a big part of its ranking from the fact that there is no alternative route for access nor egress from Fox Island in case of an emergency.
Now, the good news in this is that the rating of 7 will put us at the top of the County’s bridgepriority list for funds for replacement of the bridge.
When will the bridge be replaced? There were no commitments there. The $20-$30 million needed to replace the bridge is more than Pierce County currently spends yearly on construction projects for all County roads and bridges. There is a lengthy process of applying for grants from the State and Feds. The good news is that this year the County is finishing design and repair/replacement of three bridges that were recently funded with Federal Highway Bridge Replacement and Rehabiiltation Funds which puts our bridge (the County’s biggest, by far) at the top of the priority list. Hopefully, that energizes the process. We’ll just have to keep an eye on that.
This segues into the issue of emergency preparedness. The County engineers did say that, due to our limited access situation, emergency planning would be very important. FICRA Building Trust Board member Ray Kittelberger has been pressing this for some time. He will be convening a committee this October to pursue emergency planning with the objective of having an island-wide meeting in the Spring of 2014 to advise Fox Island residents on how to prepare for emergencies and how they can help the island-wide emergency preparation effort.
So, in short, the bridge is safe to drive on. However, it may not be the best place to be in an earthquake.
Jim Braden, President, FICRA