Sunday, February 9, 2014

PPP/DBOM Model of Building Public Infrastructure, What I Learned as a Sailor, and the San Francisco Bay Bridge

After graduating from law school I lived on a sailboat for a few years.  Based on that experience, it seems elementary to me that if you mount a fixture to a deck by drilling and bolting, you want to apply caulking in the holes and between the deck and the fixture.  You don't mount the fixture and then goop caulking around the outside ... because it will leak.  

The new eastern span of the San Francisco Bay bridge continues to have new problems.  Although we are well towards Spring, we've just had our first winter storm, and it now seems there are leaks into the bridge decking structure.

From this morning's Chronicle:
[T]he guardrails on the suspension part of the bridge are made of steel to save weight - but they are proving to be problematic.When it drew up plans for the project in 2001, bridge designer T.Y. Lin International specified that the 2 1/2-foot-tall guardrails be bolted down through holes drilled in the underlying steel structure that supports the roadway. The design called for a continuous line of caulk between the bottom of the guardrails and the steel structure. That way, water would not make its way through the bolt holes and into the hollow structure below.
Caltrans in its infinite wisdom allowed a deviance.  The contractor complained that placing caulk between the bottom of the guardrails and the steel structure would make installation harder, so Caltrans allowed caulking to be added as a bead around the outside.  Every sailor would know better, it seems. ...
Last year, Caltrans changed the plans, saying it was the "contractor's option" to apply the caulk outside the guardrails after setting them in place - much like a homeowner might lay down a bead of caulk where a bathtub meets a tiled wall.
So what happened ...
The bridge opened in September, and within three months [or more succinctly after the first storm], it was clear that water was getting into the steel deck cavern when it rains, Casey said.


Between all the stories about the defective bolts, and now these leaks, one could get the idea that Caltrans was in over their head with this project.  

Does this suggest that a PPP, with American Bridge/Fluor (in this case) assuming full design-build responsibility and obligation to maintain for 35 years, would have been a better way to go?

Caltrans speaks of a five year shake out period.  It's likely that similar issues would come up with a PPP.  They would happen not in the light of day; we'd never hear about it.  Would it be cheaper?  More efficient?  

It's not inherently obvious that the same decision on caulking would not have been made by the contractor in a PPP/DBOM context.  Of course, the concession entity would bear the cost of making good.  

Is PPP/DBOM better for the public?  Less publicity of problems is not necessarily better.  It would mean less pressure to address some of these problems.  It would not necessarily guarantee fewer problems.  


  1. Obserations in email from Sandy Zirulnik, who thinks about these kinds of things:

    I'm glad you got on this. Here are some questions that occur to me:

    1) Why do "expert" engineers seem to lack common sense? It seems totally stupid to me that you would penetrate a steel deck that you want to be waterproof in order to attach something to it. Why not shape the deck so it has a positive and/or negative "key" shape to interlock with the barrier and prevent sideways movement? No penetration necessary, nothing to leak. (Or more simply, why drill and bolt INTO the deck, when you could have threaded bolts welded to and protruding from the deck?)

    2) Answer to question 1 may be that experts are so specialized that they think only about their #1 problem, not about inter-related issues and consequences.

    3) Why don't engineering teams for big projects have forensic super-experts whose job it is to know about failure modes and keep a look-out for them throughout the design process. Surely we've had enough construction problems that there are experts in such things. Don't they teach and talk to the next up-coming crop of engineers?

    4) Why let contractor propose changes, then escape the consequences of these changes? You don't need a PPP process to have accountability process for design or construction defects.

    5) Why build marine structures out of materials that don't like to get wet?

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