Here's another longer post, in response to Ginna, who wrote about the bridge, seismic work, and where to put our money. My response didn't fit the comments section, so here is the full reply.
Here's the short answer - the seismic work on the Johnson St. Bridge needs to be done and the difference between lower and higher levels of protection is incremental. Cost savings won't be significant when you start rebuilding the piers and foundations, whether for a 6.5 or 8.5 earthquake. How much the incremental savings would I'll leave to the engineers and quantity surveyors, but it won't be enough to do a new project to rebuild the Bay St. Bridge to a higher standard. Doing seismic at Bay St. while doing extensive, similar work (even to a lower standard), will be much more expensive than one, comprehensive project at Johnson St. Bridge, where other work that can be integrated into the full seismic package can be done as part of a single project.
Some of the other work on the Johson St. Bridge has to be done now so it makes sense to do the whole package now. The impacts of extended closures required for the one project would be magnified either by doing the two at the same time, or one after the other. Both are a disaster in slow motion, but with the Bay St. bridge thrown in because it's "cheaper" (that's only plausible if you are leaving the Blue Bridge alone), the pain would be extended over a wider area or a longer time frame - neither are appealing scenarios for our transportation network or our economic vitality.
Here's a longer answer, and if you want more info on the Ashtabula Bridge in Ohio, mentioned in previous posts, the links follow the letter.
John
Thanks Ginna,
Seismic vulnerability is just one of the many factors recommending replacement of the Johnson Street Bridge.
The trigger for work is the immediate need to replace mechanical and electrical systems, compounded by our knowledge of its seismic vulnerability. Deterioration of other superstructure elements are also evident and should be repaired or replaced. It makes the most sense to combine all necessary works into a single project. Other things on our decision checklist included road safety improvements and the opportunity for a new structure purpose built to better accommodate alternative modes, particularly cycling and walking.
We have to rebuild the piers in any event, so any potential cost savings of shorting the project from a an 8.5 to a 6.5 earthquake will be incremental at best, not the orders of magnitude critics seem to assume.
Bay St. was upgraded to then current seismic standards and may stand in a significant earthquake, while the Johnson St. Bridge will not. Resilient emergency response systems provide redundancy wherever possible. Providing a Johnson St. bridge crossing at the most current standards will provide for that in a cost effective and efficient manner.
Cost effective because because shifting any incremental savings from the necessary Blue Bridge work scaled down a couple of points on the Richter scale would not provide the full funding necessary to do similar work on Bay St., which is also otherwise functional. It needs no other work at the moment that would necessitate a rebuild.
Our engineers also do not recommend refurbishing only the superstructure while leaving the foundations as they are. The investment for that work alone is extensive and costly and they will want to protect those investments to the extent possible. Why would you paint the house when the foundation is crumbling?
The other issue associated with the seismic vulnerability of the old bridge looks beyond the immediate hazards of an earthquake. The closure or collapse of the bridge will be an economic catastrophe for months, if not years following a seismic event. Once the immediate needs of dealing with death, injury and the damage to or failure of other critical infrastructure is in hand; the longer-term project of reconstruction and economic recovery will require a functional Johnson St. Bridge. After the 1989 California earthquake, studies indicated a net positive benefit for investments in earthquake preparedness and mitigation measures (including seismic upgrading of critical transportation infrastructure).
While many of the consequences may not be a direct liability of the city, our responsibility is to protect the viability and vitality of our downtown businesses and other industry that depends on the bridge (Point Hope Shipyards depends on the bridge going up, for example, and some plausible scenarios could see the channel blocked or the bridge locked shut for a period of time).
Bridges at Ashtabula and in Lorain in Ohio suffered long-term closures (not because they collapsed but because repairs were more extensive and time consuming than anticipated), but it is worth noting that those closures were tied to business failures in those communities.
Those projects are also relevant to the issue of cost escalation. Current estimates for refurbishment are Class "D" and less reliable than those for the Class "C" replacement project. Reasonable contingencies were provided for in that estimate, while the uncertainty associated with refurbishment will be greater both from the lower level at which costs were estimated, and the potential unidentified deficiencies that a bridge of this age and complexity may reveal. (The Ashtabula Bridge is a good example of hidden problems exposed after work began. Gears were found to be worn out and the bridge was closed for more than a year). *
Thus far our preliminary risk assessments suggest that the economic impact costs could exceed those of any capital project for refurbishment or replacement. Business failures that may result from extended closures after an earthquake (or for the necessary refurbishment work) will be expensive for the city as the tax base erodes or is compromised for a period of time.
In short, dividing the considerable funds needed for a primary, comprehensive project, and then over two bridges, is not cost effective nor an efficient deployment of resources.
As further work is done on the more comprehensive planning, design and costing of the refurbishment option, I'm confident it will confirm that replacement is the most fiscally and economically sensible choice. It is already clearly the most sustainable option.
See more about the Ashtabula Bridge:
Ashtabula Bridge “disaster”:
News story notes on business closures:
http://blog.cleveland.com/metro/2008/11/ashtabula_bridge_closing_separ.html
Notes on legal claims:
http://www.cclcc.com/pdf/oh1d.pdf
Wikipedia says bridge closed for more than a year (March 2008 to May 2009)
http://en.wikipedia.org/wiki/Ashtabula_lift_bridge
Also of interest – another Ohio bascule bridge, the Charles Berry in Lorain, closed overtime for repairs and hit local businesses hard.
See: http://www.morningjournal.com/articles/2008/10/18/news/mj135760.txt
No comments:
Post a Comment