Quarry Road Bridge

Matt Lohry wrote, "I noticed that the endpost is buckled upward, and not at a pinned joint--a heavy truck would exert force on the lower chord, which would normally pull downward on the verticals and buckle the upper chord where they meet. It is extremely unlikely that a large load would buckle any end chords..."

Erm, No. On a pratt truss, the verticals are under _compression_, not tension. The upper chord is pulled on by the diagonals, not the verticals.

The end posts are under compression, and when compression members fail, they buckle. Without closer examination though, it's all just guesswork.

It could have been from improper lifting - but why and how could it be lifted from partway along a sloped end post?

It could be the endpost there was damaged, thin, or lacing missing and so the overload caused the end post to buckle.

It could be the bearing came loose and allowed the end post to turn or the end to pivot making it less resistant to buckling.

Or maybe just plain, simple overload.

However, it's all just speculation at this point and from this distance.

Anyone dumb enough to waste money making a historic metal truss bridge look like a non-historic covered bridge (which only serves to add useless dead weight to a bridge, and thus further weaken the bridge) likely isn't experienced enough to understand how to properly repair a bridge anyway. I note this project was conducted in-house, and not by an experienced contractor. Some counties have proven that they can do historic bridge work in-house, but this type of work isn't for everyone, obviously.

Took a closer look at the pic and I think you are probably right Matt... doesn't look like a normal overweight load collapse.

But indeed I think the key word here is negligence!

I don't know, guys...this is not how a truss bridge normally behaves when a large downward vertical load is placed on it. Looking at the pic, I noticed that the endpost is buckled upward, and not at a pinned joint--a heavy truck would exert force on the lower chord, which would normally pull downward on the verticals and buckle the upper chord where they meet. It is extremely unlikely that a large load would buckle any end chords, since they are shorter (and more resistant to bending) than the rest of the upper chord members. With that said, I think what Scott said about proper bracing is spot on...it looks like someone who was not qualified to make the call to lift the bridge did it anyway, and they lifted at the corner where the buckle occurred, without bracing the bridge at all, and the lift point was where the buckle occurred. They pulled up, initiated the bend in the end post, and the oddball twisting forces being placed on the rest of the structure took over, and that was when the endpost finished buckling and the collapse occurred. Cause: total and blatant negligence. Proper bracing would have avoided it all.

Despite my previous sarcastic post...In reality I agree with your statement Scott. There should be no way this happens if the trusses were properly supported before being lifted...even if they were "rotted" as stated by the county engineer. It appears to me as if an overweight county truck attempted to cross it and caused it to buckle.

Hmmm. I'm no structural engineer, but it doesn't sound to me like somebody's telling the truth here. I don't see how it's possible for the truss to have collapsed like that if the bridge was being lifted properly. It looks more to me like somebody drove heavy equipment onto the bridge while attempting to "repair" it. Possibly even at the behest of some official or other who thought that repairing it was just pouring sand down a rat's hole. I know of one instance where a firefighting crew for the BLM "accidently" left an obsolete, malfunctioning tanker truck, which the powers that be refused to replace with a new one that actually worked, in the path of an oncoming wildfire. The truck burned up, it got replaced, everybody happy (except the taxpayers). I wonder if this is a similar situation.

My guess is that the bridge revolted at the idea of being made into something it's not... and just gave up.

Unfortunate loss of another pin-connected Pratt pony however.