Posted on 08/08/2007 7:59:09 PM PDT by neverdem
MINNEAPOLIS, Aug. 8 — Investigators have found what may be a design flaw in the bridge that collapsed here a week ago, in the steel parts that connect girders, raising safety concerns for other bridges around the country, federal officials said on Wednesday.
The Federal Highway Administration swiftly responded by urging all states to take extra care with how much weight they place on bridges of any design when sending construction crews to work on them. Crews were doing work on the deck of the Interstate 35W bridge here when it gave way, hurling rush-hour traffic into the Mississippi River and killing at least five people.
The National Transportation Safety Board’s investigation is months from completion, and officials in Washington said they were still working to confirm the design flaw in the so-called gusset plates and what, if any, role they had in the collapse.
Still, in making public their suspicion about a flaw, the investigators were signaling they considered it a potentially crucial discovery and also a safety concern for other bridges. Gusset plates are used in the construction of many bridges, not just those with a similar design to the one here.
“Given the questions being raised by the N.T.S.B., it is vital that states remain mindful of the extra weight construction projects place on bridges,” Secretary of Transportation Mary E. Peters said in a statement issued late Wednesday.
Since the collapse, the concern among investigators has focused on “fracture critical” bridges, which can collapse if even a single part fails. But neither the safety board nor the federal Department of Transportation on Wednesday singled out any particular design of bridge in raising its new concerns about gusset plates and the weight of construction equipment.
Concerns about the plates emerged not from the waters of the Mississippi River...
(Excerpt) Read more at nytimes.com ...
They did not fall simultaneously. In fact, the north side didn't collapse until a full quarter-minute (15 seconds) after the south end started falling. This is shown clearly on a surveillance video of the collapsw (looking toward the north shore).
I didnt hear how the rocks were distrubuted. I didnt see more than one truck on that center section of the bridge that went down first. I assume some had already been dumped in the non traffic lane.
I watched what happened.
I’ll have to find the picture I saw..it is of a section that has 4 or 5 dump trucks all together and you can see that the beds are filled. Unless I am misremembering (tm) — which becomes much more frequent these days. ;-)
The center section let loose on one end and I assume the weight caused the other end to let go quickly. The other sections of the non redundant bridge fall back towards shore due to no center span holding them together a little bit later. This was one of the last non redundant bridges built with this design (thank goodness).
The degree of ignorance about engineering matters in the popular press astounds me. I expect people to be a little misinformed, but not this mind-bogglingly stupid.
i did see a cement mixer truck that had gone done with the center section.
Yeah, like I miss not commuting across it as I have twice a day for years.
Damn, I just can never plan my vacation days appropriately.
I missed all the fun.
Shoot!
I really agree with you on the ignorance and laziness of reporters on the engineering aspects. The continuous reports of structural flaws was a perfect example.
I talked to my best friend who works down there over the w/e. He said one gal in another dep’t where he works was on the center section when it went down. Her car remained on the bridge. She survived but word has it she is very stiff, sore, and aching from the sudden stop at the end of that fall.
More appropriate.
anyone here if they recovered anymore victims today?
A bridge is only as strong as its weakest gusset plate.
Although now that I look at it, they may have actually just dumped thier loads as only 1 looks like it is full, and there is rock already dumped onto the bridge.
Still, the rock, dirt and trucks is all concentrated in one place, and it looks like it may be the span that falls straight down in the video.
Which looks to me to be the span that all the trucks, etc were on, and also was the span that the construction workers were working on.
Reid stated,”What did Bush know and when did he know it”
I agree with you. And add that sudden weight, the hammering, and the 2 lanes of traffic on the outside 2 lanes, and I think we have a reasonable conclusion.
The southern pier structure moved quite a distance during the collapse, and wound up way out of plumb. The northern pier structure stayed in place, and stayed plumb.
The southern pier still had the bearing plates attached to the top of the piers. The northern pier had the concrete pier tops ripped away violently, tearing away the bearing plates off the top of the piers.
The southern pier was undermined, possibly by years of undetected scour, and moved to the north, putting extreme horizontal forces onto the northern piers. The bridge exploded off the northern piers, and twisted up and over the side laterally. This pulled the bridge south, causing the center span to snap and fall as a unit. The extreme bending in the center span as it collapsed(from the video) shows that tremendous horizontal force was in play. As the southern pier moved south, the southern half arch lost its bearing, and fell backward, but not before pulling the southern roadway toward the bridge, which pancaked the southern road sections. At the northern end the shearing of the bridge and the twisting collapse of the northern half arch pulled the northern roadway elevated spans off their supports and pancaked them.
This all happened in a matter of seconds.
For the southern pier to move as it did, and to wind up out of plumb so severely shows that it was the weakest link in the bridge.
The bridge was not experiencing anything near its design load that day, having one half of the traffic loading and no loading for snow and ice. There was no vertical loading that took away the safety factor already in the design.Heat was not a culprit, as cold affects the strength of steel more than a hot day would.
That the NTSB is talking about gusset plates at this point is meaningless. Gusset plates are overdesigned, and they held up the bridge for forty years.Gusset plates are used everywhere in structures—look around and you will see them. All the steel will have to be examined, but my hunch is that the problem with this bridge was not in the superstructure above the arch, but more foundational, such as a problem with the foundation under the southern pier, which was adjacent to the water.
Although the recent bridge report said that scour was not a problem, with the turbidity of the water, a diver would be hard pressed to see signs of scour when they can’t see six inches under the water.
This failure was catastrophic, and the way the center span fell, almost snapped at both ends, instead of failing at one end, and then pivoting down into the river, shows that extreme horizontal forces were involved.
That’s my take on it, just from looking at the pictures taken by photographers the evening of the bridge collapse and watching the video from the lock.
Examination of the steel remains to be done, but my opinion is just that, my opinion.
Bush was here on saturday to check his work and was seen smirking. sarc/off
She came out good after this terrorist attack, created by government deficiencies in funding, and American stupidity, created by war mongering Republican political agenda against global warming concerns which was caught by savvy MSM reporting which has been taken as the 8th wonder of the world by many.
We need more government funding to prevent such a catastrophic event from happening again. /s
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