Posted on 07/12/2006 11:26:51 AM PDT by Aquinasfan
I can't imagine. Sound absorbing materials are usually angular or soft --or both. Got this from the other thread:
``I can't imagine anybody signing off on a design of suspending 3-ton concrete panels such that the failure of any one hanger would lead to 12 tons of concrete coming down on the highway," said Steve Banzaert , who teaches a course in ``spectacular failures in engineering" at MIT.I would like to know if anything like this exists anywhere else in the world. How was this design approved by layers of engineers?
"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.
"
Wouldn't surprise me at all. Neither would shorting the cement content in the concrete used in the panels. I've seen enough of that kind of nonsense in construction to make me wary of most large projects. The temptation to cut costs by contractors is just too much for some to resist.
I still maintain, though, that it is the design that is at fault here. Any design that suspends concrete panels like this one is going to suffer failures at some point. It's inevitable. A small water leak will corrode fasteners faster and anyone would believe, and can weaken the concrete itself.
So, when a panel falls on a passing vehicle...well...we've seen what happens.
I see no alternative at this point, but to remove the entire lot of the panels. Imagine the additional cost. Someone needs some prison time over this incident.
"Why replace them at all? If they serve no function, just remove them!........"
Aesthethics. Lots of visible structure with that stuff removed. Folks want a nice smooth tunnel to drive in. Ugly concrete and metal makes folks nervous when they're underground.
. . . especially when you drill through the rebar in the ceiling of the tunnel . . .
I clearly see air slots in the ceiling panels. It's an exhaust plenum. It's not structural in the sense it's not holding up the tunnel roof.
I don't drive thru tunnels looking at the ceiling. I just want to get to the end as soon as possible and live to tell about it.......
"I know that epoxy can be stronger than steel, so that wasn't necessarily the problem. Necessarily.
"
It can, if it's properly catalyzed and mixed, and if the temperature range is right, and if the material it's holding together is dry, clean and without loose materials.
I can see the engineers now, working from a spec. book from the adhesive manufacturer. "OK, let's make the safety factor 150% on this crap." Not enough, apparently, to compensate for lazy workers trying to make a deadline, or for improperly-cleaned holes where the epoxy was to bond the concrete and the bolts, or the wet hole, or the rusty bolt.
I've used a lot of epoxy in boat work. A lot. It's great, as long as every factor is correct. If it's not, it doesn't work for crap. A friend of mine had a boatyard replace the transom on a fiberglas boat. I'm not sure what they did wrong, but the first time he took it out and slammed the throttle forward on the 225 hp outboard, the transom ripped right off the boat, sinking the outboard and the boat in about 150 ft. of water.
He was OK, but they couldn't recover the boat, so there was no way to figure out how the boatyard had screwed up this repair.
Epoxy's great, especially when tested in the lab.
it's not a rumor
read this
http://www.mass.gov/ig/publ/catboltr.pdf
What an unmitigated project management disaster.
From what I read, they designed a concrete roof with dense rebar placement, but with no allowance for future drilled anchor rods, they kept hitting rebar, almost 50% of the time. Each bad hole had to be patched.
The roof was designed independent of the ceiling and was terribly coordinated.
Fast forward through numerous screwups at testing, highfailure rates, slow pace of constructions, finding crews had cut the lenghts of bolts to make them fit in the rebar grid, and huge change orders regarding the drilling of holes and installation of the anchors. The project manager allowed anchor holes to be core drilled THROUGH the rebar without consulting the original designers of the concrete roof.
Precast ceiling panels can be hung without any problem whatsoever. This installation was a disaster.
"DId you see how they were mounted? Incredible.."
I did go look at the drawings. Theoretically, it looks fine. However, the epoxy holding the bolts in place is the weak link. If everything's ideal, it would work, but in tunnel work, nothing is ever ideal.
The majority of the real estate that the Big Dig freed up is to be used as a park. The parks name is.... The Rose Kennedy Greenway!
I read it. Amazing.
That poor woman's family is going to own Boston.
I read that entire report. Just as I suspected, specs were not followed for these anchor bolts in several ways. The failure rate was way too high.
Then, they allowed the shortened bolts, or drilled out rebar. Amazing.
Now, they're going to get to remove all of those panels, I'm betting. What a disaster!
"I don't drive thru tunnels looking at the ceiling. I just want to get to the end as soon as possible and live to tell about it......."
But you see the ceiling, anyhow, ahead of you, as you drive. Trust me, you wouldn't like looking at the ceiling without some sort of ceiling. I've been in mine tunnels, and lots of other underground excavations. They're not pretty.
You won't find unfinished tunnels anywhere lay people go on a regular basis. It's just too scary.
The Washington DC subway stations sport concrete ceilings (continuous with the walls). Link to photo is here (scroll down a bit) http://fotot.jarvenpaa.net/en/0000000022 I believe the white rectangular objects visible in each square of the ceiling portions is a light weight screen of some kind, which covers vents and other mechanical items. But the main structure of the ceilings is concrete. Probably a good deal safer than the Boston tunnel design though, due to the self-support provided by the continuous arch, plus I think the grid pattern is due to an underlying structural framework of serious steel (like I-beams, not re-bar). I've never heard of a chunk coming down, and things in DC aren't exactly built by conscientious non-union workers. I think the union-mob infestation is nearly as bad there as in Boston. In the huge blizzard in the late '90s that shut down Congress for a few days, the Congressional investigation into why the roads weren't cleared discovered that at least 2/3rds of the trash collection/plowing trucks owned by the city had long since vanished, presumably sold to the mob by the union guys who were supposed to be driving them every day (and who had no doubt been continuing to collect paychecks for "driving" the long-departed trucks), since nobody but the mob buys stolen trash trucks.
Whew, heads will roll now.
I'd be shaking in my Red Wings if I were one of those guys. No way I'd want to be walking around in a tunnel where 3 ton chunks of ceiling have already fallen and there's still some up there. I do notice they seem to be sticking toward the parts with no panels or small panels, wearing a hard hat in those circumstances is kind of a twisted joke.
"Precast ceiling panels can be hung without any problem whatsoever. This installation was a disaster.
"
Yup. Had they installed hanger hardware before pouring the darned thing, they'd have had no problems at all. I know just what the rebar looks like in that concrete, and I don't know how you'd ever drill the hanger holes in that mess. And they couldn't.
If they had just designed the hangers into the original reinforcement design, all of this would have been avoided.
Epoxy my red butt! Epoxy's great, but there are just too many unknown factors in a situation like this. And never mind stupid workers who mix it improperly or skimp on something, or drill short holes and cut hanger bolts off to fit.
Big construction like this is always full of worker errors and intentional shortcuts. Feh!
The Ted Williams Tunnel, running under the harbor from South Boston to East Boston, was the first part of the Big Dig to get underway. On Dec. 22, 1992, workers lay steel rebar inside the tunnel tube in preparation for the pouring of the concrete floor. Globe Staff Photo / David L. Ryan
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.