August 6, 2007

Paving Material On Bridge Is Not News

Last night, Drudge carried a headline that linked nowhere for hours, announcing that "tons" of paving material had been on the St. Anthony Bridge before its collapse. This morning, the headline finally linked to the New York Times, which published a brief article outlining the obvious:

Trucks carrying tens of thousands of pounds of crushed stone were parked on the Interstate 35W bridge, and more stone was sitting on the deck when the bridge collapsed, investigators said Sunday, raising suspicions that the added weight of materials intended for repairs may have played a role in the bridge failure.

The chairman of the National Transportation Safety Board, Mark V. Rosenker, said investigators had questioned employees of Progressive Contractors Inc., which was doing work on the bridge deck, regarding quantities of various materials, specific equipment they had put on the bridge, and where the materials and equipment were on the bridge. The weight and location will be entered into a computer program, Mr. Rosenker said, to calculate the stresses generated on each girder and other bridge components.

We knew this on Wednesday night. The first news reports included the fact that the bridge deck had been under construction. The first images of the collapse showed the heavy equipment of the construction effort, including large trucks holding the paving material.

From the moments after the collapse, questions arose as to whether the construction work caused the failure. Yesterday's statement by the NTSB even as the New York Times reports it doesn't consist of any great revelation. Whenever road work involves regrading, the source materials have to be nearby. That will have to get factored into the collapse, but no one seriously believes that having that material on the bridge was some sort of violation or anomaly. Normal bridges handle that kind of load without a creak or a popped rivet.

It seems a silly item to tease for hours, unless someone had warned the construction company that it would threaten the collapse of the bridge, which no one expected at all. At least it's more germane than gas-tax policy, despite the foaming at the mouth of one local nutcase columnist. Let's try to remain calm and rational while the NTSB conducts its investigation into what really went wrong with the St. Anthony Bridge.


TrackBack URL for this entry:

Comments (13)

Posted by chsw | August 6, 2007 7:21 AM

Will the Army Corps of Engineers and MN National Guard put up a temporary bridge, and if so, when? The Corps did that in CT when the Mianus River Bridge (about 0.5 mile) collapsed a decade ago.

Or are the environuts delaying the temporary structure just as surely as they'll hinder the permanent replacement?


Posted by John Gault | August 6, 2007 8:06 AM

"Let's try to remain calm and rational while the NTSB conducts its investigation into what really went wrong with the St. Anthony Bridge."

What? No media speculation? No baseless political finger pointing? How would the MSM survive? They would have little to nothing to report on but the latest celebrity gossip.

Capt, you must live in a fantasy world...

Posted by k2aggie07 | August 6, 2007 8:48 AM

I heard that the rescue teams had to leave because people were taking pot shots at the helicopters. And that the collapsed caused the water to be toxic. And that there are people getting raped/murdered in the Superdome by the dozens.

Sorry Cap' ain't gonna happen like you want it.

Posted by agesilaus | August 6, 2007 9:08 AM

Ah, that material was going to be installed on the bridge deck. In otherwords the bridge is designed with the weight of that material included in the calculations. They had probably already milled off the old decking material and removed it from the bridge, thus removing an equivalent weight of material anyway.

Posted by starfleet_dude | August 6, 2007 9:23 AM

When a MNDoT spokesman is now saying that other transportation improvement projects may have to be delayed because of having to divert funds to the replacement of the 35W bridge, it's pretty obvious that additional funds will have to be raised. IMO, a rise of 15 cents in the gas tax is necessary to get the additional millions needed for a new 35W bridge while keeping pace with construction elsewhere in the state.

Posted by Bruce | August 6, 2007 9:40 AM

The cause of the bridge failure is most likely prolonged neglect and failure to address known issues for over a decade. Other than that, I do think it's interesting that Homeland Security knew that this failure was NOT terrorist related less than 5 minutes after the disaster.

Posted by jpm100 | August 6, 2007 9:54 AM

This is wild speculation, but...

Was the road surface essentially along for the ride and not structural in terms of helping hold up the bridge? Did it serve the purpose of transmitting the vehicle loads to the bridge structure, but otherwise did nothing to keep the bridge from falling down?

If so, then the road surface needed expansion joints to allow it to expand and contract in the heat.

What if the road repairs interfered with this normal temperature related breathing?

From my recollection the collapse occurred roughly within hours (maybe less) of the hotest part of the day. It was also a hot week and I forget if that was one of the hotter days or not.

The repairs may have eliminated cracks that allowed the breathing to take place or interfered with the designed in breathing.

The expansion of the road/concrete, if not allowed to breath may have introduced additional stresses on the bridge not counted for. The concrete may have been in compression in a few location.

The thing is, the concrete would have been looking to bow or buckle if it was in compression. Since the bridge was designed to withstand vertical loads, it may have been restricted from bowing in that direction. It would then be inclinded to bow in a horizontal direction. This may explain why when part of the bridge started to go, it was reported that it shifted sideways. One side of the bridge may have failed, allowing the bowing/buckling effect of the compressed concrete to shift the bridges sideways.

It just seems odd to me the bridge when on hot day with the intersection of the hotest part of the day with high traffic volumes.

/end wild speculation.

Posted by MarkW | August 6, 2007 10:22 AM


All of the statements that I saw, stated that they had no evidence that the collapse was terrorist related. Which is an absolutely true statement. They did not make the claim that it was not terrorist related.
Do you see the difference?

I suspect that if the road tax would stop supporting things like light rail and bike paths, they would have more than enough money to complete the repairs without raising taxes.

The bridge was designed to take that weight spread out over the entire span. Instead it was concentrated in a few spots. WOuld this make a difference? I honestly don't know, but I would hope the investigators are running the weight distribution through their models, not just the total weight.
On the other hand, they did have one lane closed off while they were doing the re-surfacing. This would result in a lot fewer vehicles on the bridge, further reducing it's loading.

Posted by starfleet_dude | August 6, 2007 11:16 AM

I suspect that if the road tax would stop supporting things like light rail and bike paths, they would have more than enough money to complete the repairs without raising taxes.

MarkW, here's how MNDoT's spending back in 2002-2003 broke down by transportation mode:

Highway: 93.6%
Transit: 4.9%
Aeronautics: 1.2%
Carriers: 0.4%

Even if spending on all other modes of transportation was zeroed out, there would still be a shortfall of state funding, which is why Pawlenty has gone the bonding round to pay for highway improvements. Those bonds will eventually have to be paid off, which will make the job of Pawlenty's successors that much harder when it comes to maintaining the state's infrastructure. That's why an increase in the gas tax matters, rather than just digging the state in even deeper when it comes to paying off its long-term obligations.

Posted by MarkW | August 6, 2007 11:46 AM


6.5% of $3.6 Billion is $23.4 million.

I know that in whatever world you infest, the answer to every problem is taxing people who make more than you do, but out here, the answer is frequently to stop wasting money on things that don't need to be done.

The light rail system that was just opened in Minneapolis would have paid for 4 bridges of this type.

Posted by TW | August 6, 2007 12:34 PM

Huh, a temporarily thinner deck -and- high concentrated loads. Not a good combination.

Posted by viking01 | August 6, 2007 12:41 PM

If taxes were the answer the Big Dig in Boston, Taxachusetts would be flawless.

Neglect or indifference is the cause because if being an "old" bridge is the problem then the Brooklyn Bridge, not to mention Brunel's Iron Bridge near Bristol, England would probably both be in the East or Severn rivers, respectively. Not to mention the Pont Neuf in the Paris and several Roman bridges throughout Europe.

Not long after the I-35W disaster my local paper had an article (probably AP origin) perhaps speculating that the bridge had been widened by cantilevering additional lanes parallel to the original design platform. Maybe those in the Twin Cities know if this is the case.

I doubt that materials trucks parked on the bridge are the cause. Bridges are designed not only for static loads but variable loads (sustained winds, gusts, tremors etc.). The static load keeps the burden in one place which is easiest for a structure to bear. Imagine an army tank rolling around loose inside an airborne C-5 transport aircraft and one can quickly visualize how stressing a variable, shifting load can be. Most likely the bridge failed from galvanic corrosion (interaction of dissimilar alloys) or cumulative corrosion of salt, weather, or faulty / incompatible materials. Whether the failure is neglect or inspectors' obliviousness only time will tell. Like the Big Dig, though, it's obvious plenty of incremental weakening and the precursors of that was ignored or overlooked.

Posted by starfleet_dude | August 6, 2007 1:09 PM

MarkW, over half of the Hiawatha light rail line was paid for by the federal government. Here's the overall breakdown of how that project was funded:

Cost: $675.4 million (in 2002 dollars).
Federal - $334.3 million
State of Minnesota - $100.0 million
Hennepin County Regional Rail Authority - $87.0 million
Metropolitan Airports Commission - $84.2 million
Federal Grant for Congestion Mitigation & Air Quality - $49.8 million
MnDOT - $20.1 million

As you can see, MNDoT's share of the total cost was quite minor, and can't be used as an excuse for them lacking funding for other projects.

Post a comment