All well and good but the air entrained (light weight) concrete you refer to is used mostly in commercial roofing aplications and would be too soft to withstand the rigors that a road surface has to withstand. The removal and replacement of road surface such as asphalt and concrete is a relatively new technique in light of the age of the span in question. The concern is if only one layer was placed over the existing roadway without removing the existing surface the loads multiply exponentially.

Modern bridge designs allow single members to fail without destroying the whole structure. Besides being inherently safer, the modern approach (using the same philosopy used from day one in space travel projects) means that you can REPAIR the bridge (by replacing members one-at-a-time).

Nancy Pelosi will immediately introduce a bill to prohibit highway and bridge inspections, as these
actions violate privacy and disparage workers.

Simultaneously, bills will be introduced to prohibit Fire, Police, and DOT officials from disseminating any
information which might disparage union-built highway and bridge projects, such as the results of past inspections.

Additional bills will be introduced to extend SCHIP to include all residents of Minnesota, as they either have
already been injured by the bridge collapse or they will be injured in future bridge collapses. In exchange for
this benefit, all private medical insurance will be outlawed, and it will be illegal for doctors to accept payment from
any source except the federal government.

Al Gore will make a movie which proves that the bridge would have been fine if SUV’s, trucks, and gasoline-
powered vehicles had not been allowed to use it. There will be hundreds of interviews with “scientists”
(mostly college professors) who will assert that the bridge collapsed because of Global Warming, and it’s
YOUR FAULT for using transportation, heating and cooling your home, eating food grown more than a mile
from your house, and selfishly using any lighting suitable for reading.

Ted Kennedy will introduce a bill to give immediate legal residency and citizenship to all illegal aliens
because we’ll “need all the help we can get” to quickly rebuild the bridge.

Jessie Jackson will complain that women and minorities are getting left out of reconstruction efforts,
and he’ll sue to stop all work on the bridge until he’s happy and/or paid.

CAIR will sue Governor Tim Pawlenty and Minneapolis Mayor R.T. Rybak for announcing an Interfaith Prayer Service
to be held at St. Mark’s Cathedral.

The homeless who lived under the bridge will be interviewed again and again. All of them who manage to get air time will complain that FEMA has failed to get them money or a trailer.

There will be hearings to determine whether Attorney General Alberto Gonzoles has engaged in over-zealous
enforcement of the law of gravity, and thus contributed to the collapse.

And lastly, there will be a move to impeach President George W Bush, because he took no action even after the collapse
began to stop the collapse…and he actually let the bridge deck fall to the ground.

If a material heavier than the original was used or if a new surface has been applied over the existing one without removing it then all bets are off.

Except the weight of concrete hasn’t changed drastically in the past 50 or so years. If anything, we’ve developed new ways to find high-strength, light-weight concrete. And asphalt’s asphalt (and standard procedure is always to strip then replace). Also, I believe the safety factors have become less conservative in recent decades for steel design, which means we should have had a bridge designed to withstand more than if it were designed using today’s standards.

Most failures like this are usually found at the connections.

But I’m a physicist, not a mechanical engineer…

LagunaDave on August 1, 2007 at 11:25 PM

Civil Engineers everywhere take umbrance with LagunaDave. Haven’t you ever heard the old saying LD? Mechanical engineers build weapons; civil engineers build targets.

AP

MINNEAPOLIS – Minnesota officials were warned as early as 1990 that the bridge that collapsed into the Mississippi River was “structurally deficient,” yet they relied on a strategy of patchwork fixes and stepped-up inspections.

“We thought we had done all we could,” state bridge engineer Dan Dorgan told reporters not far from the mangled remains of the span. “Obviously something went terribly wrong.”

Should we start a betting pool on how soon someone finds a way to blame Bush for this?

mlong on August 1, 2007 at 8:23 PM

2)

…how will they blame for Bush for this?

A few pieces of information for pre-emptive defense:

Federal funding for ground transportation and infrastructure has increased by 26% in the first five budgets of the Bush administration (2006 vs. the last Clinton budget in 2001). In the first five budgets of the Clinton administration (1998 vs. the last Bush 41 budget in 1993), it increased by 22%. (Source: OMB)

So there is no basis for the claims we are sure to hear that the Bush administration has “cut” funding for road/bridge maintenance.

LagunaDave on August 1, 2007 at 11:05 PM

3)

Have the lefty kooks found a way to blame this on Bush yet?

infidel4life on August 2, 2007 at 11:02 AM

Yes, the BDS has already started showing up…

Rep. James Oberstar, the Minnesota Democrat who chairs the House Transportation and Infrastructure Committee, blamed President George W. Bush’s administration for shortchanging road and bridge repair in a highway funding bill two years ago.

Bush, he said, “failed to support a robust investment in surface transportation,” adding the president insisted on only $2 billion a year for bridge reconstruction when lawmakers were pushing for $3 billion a year.

When Congress next rewrites the highway funding bill in 2009, “we’re not going to settle for a bargain-basement transportation” policy, Oberstar said.

I just had to laugh at O’Reilly’s segment that just ran. From the get-go his “bridge expert” didn’t seem to be couching many of his conclusions with the requisite wait-and-see caution shown by the rest of the news-osphere, and beating up specifically on the DOT’s inspection standards (i.e., including the assertion that “56% of all visual inspections are wrong“), suggesting they specifically were the culprit behind this particular disaster.

I couldn’t shake the feeling that I was just about to be sold something, something big…

So when the punchline came – the guy owns a company selling expensive structural analysis equipment (surprise!) and would stand to win big if the gov’t changes their inspection approach – it wasn’t exactly a surprise. Way to go bill, in that No-Spin Zone… glad we can count on you to cut through the fog, man.

RD on August 2, 2007 at 8:25 PM

Yeah, I watched that segment too. He needs to have a discussion with his Producers because they are the ones booking and, presumably, doing research on the guests. Booking that guy, in particular, was too calculated and — I think — inappropriate.

There are plenty of civil (structural) engineers to interview, including engineering professors, regarding what happened…

I couldn’t shake the feeling that I was just about to be sold something, something big…

So when the punchline came – the guy owns a company selling expensive structural analysis equipment (surprise!) and would stand to win big if the gov’t changes their inspection approach – it wasn’t exactly a surprise. Way to go bill, in that No-Spin Zone… glad we can count on you to cut through the fog, man.

The money given is not enough. We have spent about 100 billion a year on Iraq. The last transportation bill came in at 256 billion over 6 years. We need 1.6 TRILLION over 5 years to fix the problems. What Congress has passed is at least 6 times LESS than what is needed. We give Congress 2.9 TRILLION a year in tax dollars has a nation. We spend about 500 billion a year for Defense. Where the hell is the other 2.4 TRILLION going?

What is government’s answer to its failed management of our roads? Make them private. Yeah that will work. Roads should not be about making a profit, they should be about making them safe, accesible, and open to all.