Bean Counters in Bean Town

…have bean proven horribly wrong.

Big Dig project managers persuaded the designer of the Interstate 90 connector tunnel ceiling to reduce by half the number of bolts supporting each ceiling hanger, The Boston Sunday Globe reported.
The newspaper reported it obtained a 1998 memo in which an official of Bechtel/Parsons Brinckerhoff, the joint venture that supervised the Big Dig, expressed confidence that two bolts would hold up the concrete ceiling panels.
…The ceiling designer, Gannett Fleming Inc., had planned to use four-bolt anchor plates.
Unless I’m missing something, I don’t see why (the ceiling designer) requires a 4 bolt anchor plate when a 2 bolt anchor plate would be sufficient,”Robert Richard of Bechtel/Parsons Brinckerhoff wrote.

Not knowing the Bechtel guy’s background, I’ll just assume the ceiling designers were probably an engineering firm. I think they get taught to figure ‘how many bolts per bolted thingee doodle’ in school. (Right, Jeffs?)

Richard’s memo, dated June 23, 1998 and addressed to Gary Baxter, also of Bechtel/Parsons Brinckerhoff, said Gannett Fleming should either cut the number of bolts in half or submit calculations”proving that 2 anchor bolts do not work,”the newspaper reported.

That’s a helluva choice ~ prove Richards right OR prove him…right. Sure glad it’s not my name on that memo. I wonder if he got a bonus for cost cutting. And I’m curious why the design firm backed down.
Ooooh. Sucks to be them.

5 Responses to “Bean Counters in Bean Town”

  1. The_Real_JeffS says:

    I think they get taught to figure ‘how many bolts per bolted thingee doodle’ in school.
    Exactly right, THS. I don’t know all the details, of course, but methinks they really screwed the pooch here:
    Gannett Fleming officials agreed to reduce the number of bolts, calculating that the ceiling would be safe “assuming proper installation and quality of the product materials,” according to a company statement.
    Emphasis is mine.
    Back in the days when computer modeling was not prevalent, we were taught to use a decent factor of safety in structural engineering calculations, typically 2. Yep! DOUBLE IT. Given the tendency to round up during the (tedious) manual calculaitons, sometimes the actual factor of safety was 3-4. Expensive in terms of materials, but the possibility of collapse from inadequate design was seriously reduced. That factor of safety was there because of the unknown factors — you will never realize all of the forces on a structure, as much as one might try to find out.
    With computer models, you can safely reduce the factor of safety; the models are quite accurate for the structural forces involved. The problem is that it’s very tempting to shave that margin to the edge; the savings in materials and labor can be tremendous.
    I helped to survey damage after Hurricane Andrew. I was intrigued to notice that not all metal frame towers (cell phone and power line) went down from the storm. I asked, and was told that the towers that collapsed were a newer design; virtually all of the older designs survived intact. I concluded that the design methodology was the difference; the older ones survived because they were more substantial, probably thanks to the factor of safety. That’s anecdotal, of course.
    No doubt the Big Dig was modeled on a computer, and shaved to a minimum. Then this big cost cutting measure, reducing from 4 bolts to 2. No doubt the designs said that was enough….but I have to wonder if that decision eliminated the factor of safety. “[A]ssuming proper installation and quality of the product materials” is never a safe bet, and this statement is doubtless the designers’s means of shifting the legal responsibility from themselves to the contractor(s).
    Pathetic. Another prime example of micromanagement.

  2. (It also helps to have a resident expert onboard when I make engineering assumptions. Merci!)
    Even to the untrained eye and unbelieving ear, 2 bolts holding up plates over one’s head in a tunnel sounds skimpy at best.

  3. Nightfly says:

    OK, so scratch I-90 from my itinerary. Check.

  4. The_Real_JeffS says:

    Even to the untrained eye and unbelieving ear, 2 bolts holding up plates over one’s head in a tunnel sounds skimpy at best.
    Oh, it’s certainly skimpy! I might use a 2 bolt design for something really small in loads….but on the Big Dig? Man, even if they used oversized bolts, having just two means that if one fails, the entire connection effectively fails. That’s why I speculated on the loss of their factor of safety.
    In a 4 bolt design, if one bolt fails, there are still 3 to hold the load, an increase of 25% over those 3 bolts. In a two bolt design, one bolt failing means the load on the surviving bolt effectively doubles.
    Skimpy? Oh, yeah.

  5. Cindermutha says:

    Being Massachusetts, I suspect the money was taken for four bolts, and the money for two is in someone’s pocket somewhere.

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