NTSB I-35 Bridge Collapse "Findings" = Bullcrap
by Superpole
Tue Jan 15, 2008 at 07:57:40 PM PDT
This report is bullcrap, folks.
- Superpole's diary :: ::
Here's the NTSB "conclusion" released today:
Bad design, not bad construction or maintenance, led to the collapse of the I-35W bridge in Minneapolis that killed 13 people.
My understanding is there are several independent investigations ongoing regarding the I-35 bridge collapse, including one by the highly reputable Wiss, Janney, Elstner engineering firm.
The NTSB report is obviously rushed, full of double-talk and cannot be taken seriously. They should have waited until the conclusion of the other investigations-- but since 13 people died and the coming litigation is obvious, the NTSB put out their bullcrap report. I want to know who the main contractor is for the bridge renovation which was underway (and which may have contributed to the collapse) and what connections they have to the state of Minnesota and/or the federal government. I smell a Rat.
for starters there's this double-talk:
While the NTSB says it knows why the bridge collapsed, it has yet to determine exactly what caused the disaster.
Classic, eh?
and this:
NTSB Board chairman Mark Rosenker says the board does not know, in his words, which straw broke the camel's back. However, the board does know that the collapse started at the southern end of the bridge. Construction material for a new bridge deck sat on that end of the bridge.
Memo to Mr. Rosenker: the numerous tons of construction materials stacked on that end of the bridge WAS the final straw which broke the bridge. Who's the contractor that stacked the materials there? did the state of Minnesota or the contractor hire a structural engineer to determine prior to the stacking that the bridge structure would indeed safely support this massive point load placed on one section of the bridge? if yes, where is the study, structural calculations, etc. from that study indicating it was safe to stack the materials there for any length of time?
Rosenker says more than two dozen gusset plates at the southern end of the span were the problem. Two gusset plates hold together each steel joint or node on the bridge. Rosenker says eight joints were particularly weak at the time of the collapse.
"All 16 gusset plates from those eight nodes were fractured. The other gusset plates from the main trusses were intact. Gusset plates are generally designed to be stronger than beams they connect and one would not expect to find them fractured," says Rosenker.
This discovery prompted the NTSB to look at the bridge construction materials, the concrete and steel. But none of it was deficient. The problem, Rosenker says, was with the original design of the bridge.
"The investigation has determined the design process led to a serious error in sizing some of the gusset plates in the main trusses. Specifically, the gusset plates at the eight nodes I mentioned to you earlier. Basically, those gusset plates were too thin to provide the proper amount of safety in a bridge of this scale," explains Rosenker.
the last statement is utter baloney when put into this important context:
the bridge opened to traffic use in 1967-- forty years ago.
the bridge underwent two major renovations since then:
However, MnDOT did look into the bridge's design twice in its lifetime, in 1977 and 1998, when the bridge underwent expansions. Lanes were added, the thickness of roadway concrete went from six and a half inches to eight and a half inches, and the medians were heightened.
Those changes added a significant amount of weight to the bridge. But because the department didn't know the gusset plates were too thin, inspectors didn't check whether the plates could bear the added weight.
Key: Those changes added a significant amount of weight to the bridge.
Exactly. since when does a city/state add significant weight to a major bridge without FIRST conducting a thorough structural study of the bridge components to determine the bridge can safely support the additional weight? this study would have certainly included looking at the gusset plate design and condition since the plates are a crucial part of the structure.
The excuses that "nobody knew the gusset plates were too thin" or "the inspectors didn't check whether the gusset plates could bear the added weight" are utter nonsense and indicate, in my opinion, that something is very wrong here.
Rosenker contradicts his own excuses with this statement:
"However, if you are going to make changes in loads or in additional loads of traffic, higher loads of traffic, then it is prudent to recalcuate not just your gusset plates, but the entire composition of the elements of your bridge," explains Rosenker.
OK-- so where are the structural studies of the gusset plates done prior to the 1998 renovation and the one underway when the bridge collapsed?
this is nonsense as well:
Many of the gusset plates on the 35W were corroded, but according to Rosenker, corrosion did not play a part in the collapse of the bridge.
totally wrong. trust me, unprotected (unpainted) structural steel does corrode, and this corrosion can significantly impact the structural integrity of the steel.
The NTSB is obviously pointing the finger at the so called "flawed design" of the original bridge-- a very dubious and presumptuous conclusion when one looks at the two renovations of the original bridge and the tons of construction materials stacked at the south end which very likely should not have been there.
Putting the blame on the original design engineering firm (probably not even in business anymore) works rather well if you are trying to deflect the blame from the state engineers who oversaw the two renovations and the contractor who stacked tons of materials at the south end of the bridge.
If I were a Minnesotan, I'd be damned pissed and embarrassed by the NTSB "findings".
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