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.
Guess there's only one way to find out:
"OK,,,, hold my beer and watch this" :laughing: