[MineralMan]

"I don't see how any civil engineer in his right mind would install suspended 3-ton concrete ceiling panels for aesthetic reasons only. A light metal or plastic mesh would have worked just fine, and been a lot less expensive. It seems to me that this was make-work or make-expense."

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I think you're absolutely right. Suspended ceilings work fine when they're made of lightweight materials, but this concrete business was an accident waiting to happen.

One of the reasons for them, however, may have been more than aesthetic. The concrete looks substantial, and that may have made drivers feel more secure in the tunnel.

However, psychological stuff doesn't hold concrete up, it seems. The problem, now, is that there won't be any confidence in the remaining ceiling materials. And, perhaps, there shouldn't be.

I'm guessing they didn't engineer a high enough safety factor for this material. As corrosion of the supports progresses, more of this stuff is going to fall.

I predict that it will all be replaced, perhaps with the lightweight materials you mentioned.

[Aquinasfan]

I'm guessing they didn't engineer a high enough safety factor for this material.

They may have, actually. One rumor going around is that when the construction crews drilling the holes for the tie-backs ran into rebar, they stopped drilling and cut the bolts short.

But the point remains, why build an accident waiting to happen? Especially when a cheaper, safer solution is available.

As corrosion of the supports progresses, more of this stuff is going to fall.

Another risk.

[Red Badger]

I predict that it will all be replaced, perhaps with the lightweight materials you mentioned.

Why replace them at all? If they serve no function, just remove them!........

[jwalsh07]

The "drop ceiling" is was made of concrete because they designed in high speed fans to move fouled air out of the tunnel between the structural tube and the concrete drop ceiling. They can probably justify that although I'm sure Joe Politco and Charlie the Concrete guy had a thing going.

But it really should not be a problem to hang three ton slabs from a structure the size of the main tunnell tube. I've hung more than 6 tons off small slabs in hospitals while installing equipment many times. But we never hang big loads off slabs without horizontal members into columns.

Additionally 1/2 inch grade 8 bolts, which we always use are good for about 10 tons in tension and 9 in shear. So it's doubtful their was a catastrophic bolt failure in tension.

My best guess as a blue collar guy is that there were no horizontal members, so everything was in tension which is fine load wise until things in tension start moving to and fro a little bit eventually leading to the anchor point failing. Couple that with possible substandard concrete, hole depths that don't meet spec and shoddy epoxy work and you have the Mass Employment Act of 1995 in big kimshi.

All educated guesses though.

[sionnsar]

but this concrete business was an accident waiting to happen.

DId you see how they were mounted? Incredible...

[gridlock]

Now the contractors can put in the Mother Of All Change Orders (MOACO) to take out all that concrete to replace it with something more lightweight.

Shame a woman had to die, and all, but omlette/eggs, you know?