I35 bridge revisited

[greg334]

I ended up being stuck at the scales coming into Colorado today for a while and I got a chance to talk to one of the Colorado’s safety people while they search a couple trucks in front of me for drugs (pretty cool show I must add and the guys got pinched).

We were talking about bridges, mainly the ones in Utah that scared the h*ll out of me going over and I mentioned the I35 bridge. He told me that they had a big meeting about the bridge and it was pointed out that the thing was designed and built during a time where the weight of the trucks were less than what they are today and with the four major revisions of the laws governing the weight limits on interstate highways, the chances are that the bridge was never properly updated structurally. He also mentioned that with higher traffic volumes, there is a chance that the harmonics of the traffic actually did the damage to collapse the bridge but the NTSB hasn’t ruled that out.

 

[FireGears]

It seems to always take a pile of bodies to get
the safety codes/laws improved.
I'll use the building codes as an example...

80-years ago lots of folks were dying in building fires.
As the body count increased, better building codes were demanded.
It took roughly another 50-years and MORE BODIES to arrive at the
building life safety codes of today ...
Codes which often require the retrofitting
of safety features on existing buildings.

Now a new problem is exposed...
An old, rusty bridge finally fails and produces a pile of bodies.
Why??? This bridge was "designed and built during a time where the weight of the trucks were less than what they are today and with the four major revisions of the laws governing the weight limits on interstate highways" .
Many levels of government will now begin to acknowledge this "new" life safety hazard.

QUESTION ... how many years will it take and how high
will the body count rise before THIS building code
is finally improved and the retrofitting completed..?? ..!!

 

[greg334]

Well as much as this is a complete and utter tragedy, 7 deaths are not a pile of bodies – but one death is enough to be a tragedy.

Life itself is a hazard but I still go back to the responsibility should sit squarely on the shoulders of the past and present governors of the Minnesota, no one else.

Well anyway...

The problem I was trying to point out is that the standards are there but the retrofitting of the bridge to bring it up to modern standards may not have been done properly.

Many cities and states are always updating some of their building codes but don’t forget we don’t have a standard for road construction for the interstates, we have a minimal standard and that is it. I think this was the biggest mistake – not having a defined standard for everything from signage to stripping to the base and thickness of the road itself – each state has some latitude to work with. California for example does not understand that mile markers would help a lot of us, but they may have used the wood and metal to build taco trucks or some skate boarding rec center.

After I posted this, I tried to find out more information about the NTSB’s report that was done in ’93 on the problem they found with the increase of truck weights and the infrastructure but could not find that report. He mentioned the report as the guideline being used today in many states and told me that it has a clear defining description of the different weight limits from 1953 to 1993 used in the trucking industry. The increase is not that great, but when I think when you look at the increase of the amount of trucks over that period, there is a significant increase in the weight that these bridges carry.

The point I guess I am trying to make is that even though the increases may not be that significant for individual trucks, it is the accumulation of weight across the bridge at any given moment that counts in combination of the harmonics from the traffic that matters and there must be a reexamine of the weight limits of these older bridges to ensure the margin of safety is maintained.

I think that if we really want to solve the problem and I know I will catch all kinds of comments about this one, maybe we need to think about reducing axle weights and foot print weights until we can get a grip on the multiple problems of the bridges and get them fixed.

 

[FIS53]

While you do make a decent point you must remember that for different states there will be different requirements. So you have to have a minimum standard as a starting point. Therefore all bridges must meet a certain minimum of weight capacity etc.

The northern states have the larger problem with temperature variations from +90 to -45 degrees. That means there will be adjustments above the minimums to accomodate. Further the northern states use salt and other ice clearing solutions that wreak havoc on steel structures and a different paint and other coatings and materials have to be used to again accomodate.

There are therefore differences and so as time marches on and we have changed our driving habits, many have gone to smaller vehicles than there were readily available back in the '50s. What does that matter? Well today we have more vehicles on the road, more stopping on a bridge and now with smaller vehicles means more can fit in the same space as the older ones. Yes smaller is lighter but with everyone buying every option possible the weight difference starts becomeing smaller and with more on a bridge than years ago, we get more weight and more shifts in the load on the supports. Remember the SUV of today is smaller than the older chev or ford cars of yesteryear and they weight almost as much.

I'm afaid that no one has been looking at the entire effect of the larger motoring public has on the various infrastructure.

Rob Fis

 

[Moot]

Below is a link to some thumbnail proofs of the I-35W bridge collapse.

http://www.conphoto.net/collapse.html