Crossing a unknown bridge with equipment

[Builder]

Wish I still had my small dump......
Biggest known truck to cross bridge is propane delivery truck. I gotta think it's a 33K truck. The difference is that we'll be crossing it at least 10 times in 2 days, but it's gonna be ~33K same as propane truck.

I'm 95% sure it'll be fine, but if I damage it, I don't want to be the party to blame. I thought maybe some thick 12" wide planks temporarily fastend to the bridge planks might help distribute some more weight.

 

[Lt CHEG]

I think the backhoe is probably a good idea for this one. It'll move more material but still not be as heavy as a loaded dump truck. Another option might be to dump the load on the near side of the bridge and use the backhoe to pile it up on the other side of the bridge. You could then drive the empty dump truck over the bridge and load it up with the material. Then drive the dump truck to where the material needs to be and tailgate spread it, etc. It certainly isn't as quick as just driving the dump truck over the bridge but if the material has to go any distance from the bridge then it is probably much quicker than just taking a bucket load of material at a time.

 

[LD1]

If you have any idea at all...I'd still like to know how/what the bridge construction is made of.

And how deep is the creek/gourge it is spanning. If you are considering 12" planks attached, wouldn't it be easier to form a temporary support at mid span and just drive the dump over it?

 

[Transit]

Have you looked at the underside of the bridge, what condition is it in? planks will distribute the weight but do little for the deflection of the span. If the local fire department will not cross the bridge that's telling you something.

 

[Builder]

It crosses a small stream. There's enough room under it to crawl under-maybe 5' high. I'm pretty sure the beams are ~ 10" high I or c channel on about 30" centers, but I'll have to take another look. Bridge deck looks like true 3x8's. Some are a little suspect looking. Concrete walls on both sides look pretty good.

 

[LD1]

I wouldn't have a moments hesitation about crossing it. Provided the planking and concrete is sound.

You said that you would be crossing in a 33k truck. That puts roughly 25k over the rear axle.

Using l/360 deflection limitations, (14 x 12)/360 =.46. That means the bridge would be allowed to flex .46" in the middle without doing any damage, collapsing, or staying bent permanetly.

Using a W10 x 19 I-beam (which is at the low end of the 10" beams) it would take 14000 lbs to be at the .46" limit. @ 30" centers I am assuming there are at least 5 beams which would make a 10ft bridge.

With 5 beams it would take 70,000lbs plus, right in the middle, to make the bridge deform. Of course the load wont be evenly distrubuted but the L/360 aldready has a good bit of safty factor built in and if the decking is solid, I wouldn't worry none. And with only 14' to cross, your front should be off the bridge before the rear's enter.

If they are heavier than a 10 x 19 beam, that is just icing on the cake. A 10 x 19 only has 4" flanges and a .250 web and would hold up. If you knew all the measurments of the beam, I could give you more info.

I don't think you have anything to worry about, but as others mentioned, a waiver is a good idea. Or maybe even suggest to the owner that HE have an engineer come out and rate the bridge. Did you ask him if he had an engineer design the bridge, if so, it should have a max rating. If is is a homemade bridge, maybe he'll foot the bill to get it rated.

 

[MarkV]

Call the fire department and see if someone would come out and say it they would cross it. If they will not you should not and you have a good reason to tell the customer why it will cost more to move it by tractor rather than truck.

MarkV

 

[Builder]

I wouldn't have a moments hesitation about crossing it. Provided the planking and concrete is sound.

You said that you would be crossing in a 33k truck. That puts roughly 25k over the rear axle.

Using l/360 deflection limitations, (14 x 12)/360 =.46. That means the bridge would be allowed to flex .46" in the middle without doing any damage, collapsing, or staying bent permanetly.

Using a W10 x 19 I-beam (which is at the low end of the 10" beams) it would take 14000 lbs to be at the .46" limit. @ 30" centers I am assuming there are at least 5 beams which would make a 10ft bridge.

With 5 beams it would take 70,000lbs plus, right in the middle, to make the bridge deform. Of course the load wont be evenly distrubuted but the L/360 aldready has a good bit of safty factor built in and if the decking is solid, I wouldn't worry none. And with only 14' to cross, your front should be off the bridge before the rear's enter.

If they are heavier than a 10 x 19 beam, that is just icing on the cake. A 10 x 19 only has 4" flanges and a .250 web and would hold up. If you knew all the measurments of the beam, I could give you more info.

I don't think you have anything to worry about, but as others mentioned, a waiver is a good idea. Or maybe even suggest to the owner that HE have an engineer come out and rate the bridge. Did you ask him if he had an engineer design the bridge, if so, it should have a max rating. If is is a homemade bridge, maybe he'll foot the bill to get it rated.

That's what I'm thinkin'. My dump is a long wheelbase (170") by the time the front axle gets to the other side, the rear axle will only be just getting on the bridge. However, I'm having the stone delivered and it will be a stubby dump-probably a 2' shorter wheelbase.

 

[Transit]

Good analysis LD1. We have some unknowns; how old is the bridge, how often has it been maintained, has it ever been rated? A five foot drop is not much; then again when you have 30k+ pounds strapped to your butt you have to add in the pucker factor. You are not dropping a wheel into a pothole, truck rolled over on the drivers side and tons of stone on you.
I can understand your need for the business in these times, but sometimes its better to go down the road. Look carefully and look twice more from every angle.

 

[LD1]

Even a shorter wheelbase isnt going to change that much. The highest stress on the bridge will still be when the rears are at dead center. A 2' shorther WB would give it a 12' overall wheelbase. With the front 1' from being across and the rears only on by 1' wouldnt stress the beams by near as much as ust the rears in the center.

I was just also pondering your suggestion of driving the BH across 1 bucketload at a time. This may even be more dangerous than the dump, but I dont know for sure.
With a weight of roughly 8.5 ton, and maybe another ton in the bucket, that is almost 20k itself. It has a much shorter WB and even a narrower contact patch with the bridge than you dual rear wheel dump truck. I just wonder how the 3 x 8 planks 30" on center would hold up if you drove right in the middle of 2 of the beams. The duals on the rear of your dumptruck probabally give a much wider contact patch.