Re: Bridge Ratings and Tractors

Posted by Billy NY on June 11, 2006 at 06:25:48 from (152.163.100.74):

In Reply to: Bridge Ratings and Tractors posted by Uncle on June 10, 2006 at 14:22:11:

I've seen what a tri-axle log truck looks like, after the brige collapsed, it had fallen in and was wedged where the span used to be. This was a light duty bridge and I don't recall if it was privately owned or what, but the results of it collapsing was obviously not a good thing.

This is one of those things that you really should get the intimate details about, with the resident engineer in the munincipality and or whomever the presiding authority is.

When you think about a span, you have to realize that it does have a maximum live load, hopefully with some safety margin beyond that.

When you drive your rig over the span, each of the axles are going to impose/transfer a portion of the gross overall weight of your truck/trailer combination onto the span. Like was mentioned if it works out that none of the axles point load the span in excess of the maximum allowable load, it's possible that it may work, but I'd make sure someone gave me authorization like the engineer after doing some calculations and or whatever it takes.

I recall while in college, we used to build beams of concrete and place them in a machine that had a roller that imposed a live load to the beam, you could apply enough weight to it until failure, then analyze the results depending on what section of it failed, left, right, or middle section. The roller is kind of like an axle of a loaded truck, deflecting the beam until failure, with the exception it's just one beam not an entire structure.

Not trying to lecture here, it's an interesting subject, how things like this actually work.

Another thing to consider, the design may say one thing on paper, but what is the actual condition of the bridge,is it of modern construction or an older one? Has it been de-rated, or inspected recently to insure it's still capable of it's original design loads ? That is an important aspect of this. If it's even remotely questionable, I'd not even go near it until it was properly inspected and evaluated and the ok given.

In addition to that, because I'm such a detailed orientated pain in the behind, having worked with structural engineers closely on many projects, I'd measure the axle to axle distances, width of the axles etc. get the loaded truck and trailer weighed, and include that for submission to the engineer, requesting permission to cross the bridge as configured and or something along these lines, I'd want some sort of approval in writing. Providing this information is not all that complicated, get to a scale, measure everything, call the person up, ask if any other information is needed and send it in, let them bear the responsibility of providing a definitive response of yes or no.

Guessing, like was mentioned, it's like gambling, with the odds stacked against you.

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