Beam stiffness changes by the cube of the change. So a beam twice as tall is 8 times stiffer.
Eric
A factor two, squared (2x2) was four, last time i calculated a bridge
maps.app.goo.gl
Switch to satellite view to see the bridge
I calculated this home made bridge for my mate, spanning 12 meters between the abutments.
The waterway council had a say in it, and because i am not a civil engineer i calculated a bit rich for the building permit.
Found the minimum average foundation to soil contact pressure for our sool type, didnt know about the rules for pier washout so we put the piers at the same level as the canal bottom, just to make washout precautions unnecessary.
We ordered some prefab inverted T shape retaining walls, i converted the manufacturers rated side load to a bending moment, converted that to a maximum vertical load. It surpassed actual loads by a factor of 7 to 10, both in surface load as well as bend moment where the T joins.
For deck i calculated 4 beams IPE 500 were enough to carry 60 ton with a safety margin of two. The seller only wanted to sell all 9 at once so we ended up welding flat strips between all 9 of them, to create a 4 meter wide bridge with a fail point of 300 ton.
Dressed up with links to data used, both generic foundation load as well as retaining wall element manufacturers specs, they just stamped it for approval and gave us the green light
The water council payed him a temporary log bridge beside the old bridge, which took a contractor longer to build than it took us to build the permanent bridge in the location of the old bridge. I bet ours was a fraction of the cost too.
I assume at the waterway councils office, a civil engineer had a big grin on his face while shaking his head when he stamped the approval sign on the plans
The old bridge was built in the 60s when gramps and uncle bought the land across the canal and wasnt used with the slurry tank for the last two years because 50 years took its toll on the tiny I beams, but we expect this bridge has so much reserve that it will take 150 years of decay before you must stop using it with 60 ton combinations.
Cost: 6000 euro for the used beams, 500 euro a piece for the retaining wall elements used as abutments, maybe 500 euro for the flat strips, and a bunch of welding wire.
Another mate worked as a crane operator and hoisted the stuff in place on a saturday, and the local contractor came with a 15 ton digger to dig the abutments.
We chose to dig in the wet, so the hole wouldnt collapse from water seeping in (theres no chance to pump the dug pit dry with infiltration pipes, so close to the canal, without damming the entire canal)
Had it been done by a civil contractor, it would have cost 120.000 euro and had a quarter of the technical reserve.
