Boston Big Dig

Tom's consulting role on the galvanized bolt corrosion question, before the ceiling collapse that killed a motorist. Used to demonstrate the engineering-judgment clause of the code: a non-conformance (out-of-sequence galvanizing) didn't have to mean uninstalling all the bolts; comparative analysis of zinc throwing power between hot-dip and electro-galvanized coatings showed the disputed bolts were safer than the as-built electrical hardware adjacent to them.

The Big Dig — they brought me in. They had some hangers in the tunnels holding the roof up. This was before the one that collapsed and killed the woman; this was while they were still under construction. Some of the big steel bolts that were going to hold up the roof were supposed to be galvanized — coated with zinc in a particular way. The contractor had done it out of sequence, and the question is whether the threads on the bolts — big bolts, an inch and a half in diameter — were going to rust in service.

Tom's 2001 tour. Used to illustrate cable-stay tensioning precision — strands must match length within a quarter inch or stress concentration causes cascade failure.

Anyway, there's a lot of interesting bridges. This looks sort of like the Bunker Hill Bridge, but it's not — it's a bigger cable-stayed bridge. The cable-stayed bridges are an interesting design. I got a tour of the Big Dig back in 2001, and they have to basically pull those strands within about a quarter of an inch of being all at the same length, otherwise you have too much stress on one of them. One strand of the wire rope snaps, and then another one snaps.