I 35 bridge collaps in Minneapolis

clone52 · 08-02-2007, 12:56 AM

Originally Posted by throwittoblythe

I get your point, but I was referring to the traffic load itself. If a bridge isn't expected to see bumper to bumper traffic on a regular basis, then you wouldn't assume that in design. An example would be a rural bridge; you know that won't ever see bumper to bumper traffic, so you do a traffic study to see what type of loading it needs to handle. Who knows what the traffic was like in that part of the Twin Cities back in the 60s. I know cars haven't changed a whole lot, but the number of people sure have.

Basically, the whole idea is that things are being used today for situations other than what they were designed for. Our interstate system in Iowa will deteriorate at a faster pace now because of the 70 mph speed limits over most of it. When I-35, I-80, etc were designed, they were not designed to take 70+mph at a constant rate. This is just one example.

Static loading you would assume bumper to bumper. It has to support that weight even if it won't see it very often. Dynamically though, yeah, youwouldn't assume it always had that.

See my previous post about my theory of where the collapse started. I think it failed in the seam above the train. Everything else I think can be explained from that starting point.

ornryactor · 08-02-2007, 01:47 AM

What concerns me about this has a bit to do with the discussion about how the US is outgrowing the interstate system. This bridge (a major part of a major interstate in a major metropolitan area) collapsed in what, 6-8 seconds? And how long will it take to redesign and rebuild? 2 years, I would imagine. If they made it a high-priority rush job (and they may, but I won't count on it) they could probably get a bridge thrown up in 8 months, but they're not going to rebuild that hastily. Meanwhile 35 East is going to see a very nasty jump in traffic, which doesn't bode well for the integrity of that interstate.

Dave19642006 · 08-02-2007, 06:15 AM

could it be the way and where the steel was produced , let alone not to exclude the pollution that we are experiancing? This could cause the failure of the bridge.

All structures must be designed to carry all foreseeable loads with a suitable factor of safety. Clearly it would be unsafe to walk on a structure that was adequate but had no margin of safety built in. With this in mind, most countries have standards that prescribe the required minimum safety factors for structures. The minimum is usually a factor of about 1.7. This is not a factor to allow for overloading or poor workmanship. If there is a possibility of overloading or poor workmanship, the design loads must be increased to account for the overloading and the strengths of the materials upon which the design is based must be reduced to account for the poor workmanship. The safety factor must remain complete, as it is there to account for the unexpected events and unforeseen circumstances. If a structure becomes worn, loose, cracked or corroded, it should always be repaired so the safety factor is preserved.

There are two conditions that a structural designer must keep in mind. One is "stability" and the other is "serviceability". Stability of a structure means that it can resist the loads acting on it satisfactorily and that the structure will not collapse immediately (that is, it provides enough time to escape to safety). Serviceability refers to certain conditions that are required so that the structure remains serviceable. For example, consider a bridge that can resist service loads without collapse. This is a "stable" structure. Now assume that this bridge shows abnormal deflections. The deflections could be such that the bridge feels bouncy and could lead to steering problems for vehicles crossing it at high speeds. As such this may not cause the structure to collapse. So we can say that the structure is stable, but according to serviceability criterion it is not serviceable because people could feel afraid of using the bridge.

Now we all probably heard that there was work and construction on that bridge. Traffic was seperated also to a 2 lane (?) while work was being performed.

jdoggivjc · 08-02-2007, 06:45 AM

Originally Posted by ornryactor

What concerns me about this has a bit to do with the discussion about how the US is outgrowing the interstate system. This bridge (a major part of a major interstate in a major metropolitan area) collapsed in what, 6-8 seconds? And how long will it take to redesign and rebuild? 2 years, I would imagine. If they made it a high-priority rush job (and they may, but I won't count on it) they could probably get a bridge thrown up in 8 months, but they're not going to rebuild that hastily. Meanwhile 35 East is going to see a very nasty jump in traffic, which doesn't bode well for the integrity of that interstate.

I understand for infrastructure purposes they have to get a bridge up quickly, but would anyone living up there at this point be comfortable with an "8 month rush job?"

jdoggivjc · 08-02-2007, 07:41 AM

They now have a video from a security camera of the bridge collapsing on CNN.com - Breaking News, U.S., World, Weather, Entertainment & Video News

brianhos · 08-02-2007, 08:31 AM

Originally Posted by jdoggivjc

I understand for infrastructure purposes they have to get a bridge up quickly, but would anyone living up there at this point be comfortable with an "8 month rush job?"

The minnesota DOT is already claiming 3 months to get a new one up. That seems insane. But this is probably the busiest piece of highway in the state, so it should get a lot of resources.

cycloneworld · 08-02-2007, 08:42 AM

Originally Posted by throwittoblythe

They interviewed a Civil Engineering professor from U of Minn. that had experience with this bridge and he made a very good point. The bridge did not fail in just one spot, the whole thing came down at once. To me, that points to a failure in design. There was one other bridge in Ohio that did this and it was a very poor design. One of the upper cable supports snapped and caused a chain reaction which made the entire thing come down in like 10 seconds.

I don't think its a design failure because typically it doesn't take 40 years for the failure to be seen. I would guess that the construction equipment/construction itself played a big role in this.

Terrible situation...

jdoggivjc · 08-02-2007, 08:53 AM

Originally Posted by cycloneworld

I don't think its a design failure because typically it doesn't take 40 years for the failure to be seen. I would guess that the construction equipment/construction itself played a big role in this.

Terrible situation...

I hear you on that, but I'm not sure that the construction equipment would do that either. Only half as much traffic capacity as that bridge could hold was on the bridge due to surface repairs. I'm not sure that the construction equipment would make up for more than the other half that would have been on the bridge. Also, I've been hearing on CNN that there have been signs of "fatigue cracking" appearing as late as last year. Something to me just isn't kosher with this situation.

cycloneworld · 08-02-2007, 09:04 AM

Originally Posted by jdoggivjc

I hear you on that, but I'm not sure that the construction equipment would do that either. Only half as much traffic capacity as that bridge could hold was on the bridge due to surface repairs. I'm not sure that the construction equipment would make up for more than the other half that would have been on the bridge. Also, I've been hearing on CNN that there have been signs of "fatigue cracking" appearing as late as last year. Something to me just isn't kosher with this situation.

Good point. Unless having all loads concentrated on 1 side of the bridge (because of the lane closures) had something to do with it. I'm a water/wastewater CE, not a structural one.

throwittoblythe · 08-02-2007, 09:20 AM

It's all speculation at this point. We can all say "I think x, y, z" but we won't know for sure until a full investigation is completed. I just heard on CNN this morning that they have gone to a recovery instead of a rescue situation. Which means they're not looking for survivors anymore, just trying to clean up the aftermath. I can't imagine being one of those families out there still waiting to hear.

What's sad is that somehow the city/state is going to be to blame because ultimately it's their bridge and their responsibility. However, we probably won't see anyone held accountable. Even if it was a design failure, the engineer(s) who designed that bridge are probably 6 feet under by now.

bostinelosd · 08-02-2007, 09:21 AM

Maybe we should go back in time and get the Egyptians, Romans, and Greeks. Bring them back here and have them build things. They seemed to have made some quality stuff back then. I know its a freak accident and I dont like to point fingers because it could happen anytime to any structure. Tragic.

ornryactor · 08-02-2007, 09:21 AM

Yikes. Can anyone say 'scary'?

According to a Des Moines Register analysis of 2006 U.S. Department of Transportation data detailing the condition of the nation's bridges, Iowa has about five dozen spots on Interstate Highway 35 in need of repair.

IN NEED: Of about 175 bridges carrying I-35 through Iowa, about 64 probably need some rehabilitation, according to federal rating standards.

POOR: Of those, eight are rated so poorly that they may need to be replaced. Among those eight, six are "structurally deficient" and two are "functionally obsolete."

WHERE: Five of the eight are in Polk County, three are in Warren County. All were built between 1957 and 1960.

throwittoblythe · 08-02-2007, 09:22 AM

Originally Posted by Dave19642006

could it be the way and where the steel was produced , let alone not to exclude the pollution that we are experiancing? This could cause the failure of the bridge.

This could cause a failure, but you wouldn't expect that to take 40 years. I mentioned the bridge in Ohio that failed in an earlier post and steel molding was the reason to blame for that failure. One of the end pieces for the cables cracked during molding and no one noticed/reported it and it turned out that piece was the trigger for the failure.

throwittoblythe · 08-02-2007, 09:23 AM

Originally Posted by Des Moines Register
According to a Des Moines Register analysis of 2006 U.S. Department of Transportation data detailing the condition of the nation's bridges, Iowa has about five dozen spots on Interstate Highway 35 in need of repair.

IN NEED: Of about 175 bridges carrying I-35 through Iowa, about 64 probably need some rehabilitation, according to federal rating standards.

POOR: Of those, eight are rated so poorly that they may need to be replaced. Among those eight, six are "structurally deficient" and two are "functionally obsolete."

WHERE: Five of the eight are in Polk County, three are in Warren County. All were built between 1957 and 1960.

This is exacly what I'm talking about. No one wants to put money into replacing/repairing old structures, they just want new, more modern structures.

cyclonekj · 08-02-2007, 09:27 AM

Originally Posted by throwittoblythe

What's sad is that somehow the city/state is going to be to blame because ultimately it's their bridge and their responsibility. However, we probably won't see anyone held accountable. Even if it was a design failure, the engineer(s) who designed that bridge are probably 6 feet under by now.

After a tragedy like this, there are many things that need to have priority over finding a scapegoat for the failure. Does finding someone at fault restore any of the lives lost?