2manyrocks
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Build a great structure, but skimp on the abutment and then the creek bank will wash away underneath. Nature is going to look for the weak point.
Starting my bridge!!
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Sodo
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Plus 1500 lbs of dirt in the bucket for 5500 lbs tractor weight?
And a mower on the 3-point?
That cable will increase strength substantially.
Maybe consider double cables, cuz you have extra.
Each with independent (redundant) mounting that one cable can hold the design load even if the other broke.
A truss-railing 2 feet high can add substantial strength - 5X as strong is easy.
Also that 2X6 cable-standoff in the middle, maybe weld a cross brace to the other side to ensure it remains vertical?
I'm with ya brother if I had free steel I'd build all kinda stuff!
And a mower on the 3-point?
That cable will increase strength substantially.
Maybe consider double cables, cuz you have extra.
Each with independent (redundant) mounting that one cable can hold the design load even if the other broke.
A truss-railing 2 feet high can add substantial strength - 5X as strong is easy.
Also that 2X6 cable-standoff in the middle, maybe weld a cross brace to the other side to ensure it remains vertical?
I'm with ya brother if I had free steel I'd build all kinda stuff!
deezler
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Good to hear. But I'm pretty curious how you build abutments after the bridge is already in place? Looking forward to the pics!
Good to hear. But I'm pretty curious how you build abutments after the bridge is already in place? Looking forward to the pics!
11’ x3’x18” deep slab
Post hole digger down approx 3’ in 2 or 3 spots as “anchors”
Concrete will encase approx 4” of the 6” tall tubes.
Rebar welded to tubes at various points and welded to some bar in the slab
With the 2x6 stringers laying flat it's going to be very flexible, even with a support at mid span. What type of vehicle do you want to drive across it once completed?
Streetcar
Veteran Member
In stall your reinforcing king truss as soon as you can. Additional dead load of bracing and deck will help load it
pmjerding
New member
Having free material is a good problem to have.
Sodo
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“Pin” piles of 5/8 rebar?
Lots of them.
Keep welding them end for end until they hit hardpan. Weld together and form your concrete around them.
Lots of them.
Keep welding them end for end until they hit hardpan. Weld together and form your concrete around them.
Just keep pounding pieces of rebar till hard pan? Hard pan can’t be more than 4-5’ deep by me.
We don’t even use septic systems with leech fields……ground doesn’t perc.
8-10 should be good?
Skip the post hole digging to make concrete “anchors”?
Different ideas are always welcome!
Won’t be working on the bridge for a couple weeks.
My welder is on my work truck and I don’t bring it down when the family all goes down.
dodge man
Super Star Member
My degree is in civil engineering and I had structural engineering classes also. I am by no means a structural engineer so take this for what it’s worth.
I never studied, heard of or ever seen a steel structure pretensioned with cables. I’m not saying it won’t work, I just have my doubts. With concrete beams they often pretension or post tension them with cables embedded in the concrete.
I also think I saw someone throwing out the idea of building rails to truss up the main beams with rebar welded up. Once again, I feel that’s not going to do a thing. That’s not what rebar is designed for and I don’t feel the welds would hold. Look at through truss bridges the way the joints are bolted and have gusset’s to strengthen the joint.
I‘ll add I think you’ve got a good bridge, nice build, quality construction, I just think you want to be careful what you drive across it. You’ve got those main rectangular tubes to carry the main load and I’m not sure at this point you can improve on it. Sorry I’m trying not to be to negative.
I never studied, heard of or ever seen a steel structure pretensioned with cables. I’m not saying it won’t work, I just have my doubts. With concrete beams they often pretension or post tension them with cables embedded in the concrete.
I also think I saw someone throwing out the idea of building rails to truss up the main beams with rebar welded up. Once again, I feel that’s not going to do a thing. That’s not what rebar is designed for and I don’t feel the welds would hold. Look at through truss bridges the way the joints are bolted and have gusset’s to strengthen the joint.
I‘ll add I think you’ve got a good bridge, nice build, quality construction, I just think you want to be careful what you drive across it. You’ve got those main rectangular tubes to carry the main load and I’m not sure at this point you can improve on it. Sorry I’m trying not to be to negative.
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ning
Elite Member
I suspect that there will be considerably more than 5000# of tension on the cable - there's considerable mechanical disadvantage in resisting the collapse of an arch (or resisting a flat surface from becoming a negative arch) unless the angles in the framework resisting it is fairly large. This is why the trusses on a bridge are so tall, so that the angles are large.
[caveat - I'm not an engineer, but I understand triangles, that these triangles are barely worth considering triangles for strengthening purposes!]
With a 6" tall triangle under the bridge standing off a tension rod (or cable), and a 9' wide triangle (for an 18' span), because of the really shallow angle formed in that triangle, you'd end up with huge tension on the rod - probably 15x of the downward weight it's supposed to counter.
If you want to counter 5000# using the tension, your 5k turnbuckle would explode.... even 1/2" grade 60 rebar can only be expected to hold 15k tension (gr 60 rebar - 90k psi tension - 1/2" rebar will have ~0.2 sq in). 1" gr 60 rebar would hold about 72k tension, which is what 4800# over the bridge would put on such a system.
With a 12" tall triangle, the tension would multiplier would be about 10x (vs 15x with the 6" triangle) because the angle is larger, and the rod would have accordingly less tension on it.
An 18" triangle gets a 6x multiplier.
The taller the triangle is, the lower the tension multiplier gets; if your bridge was over a canyon and you had a 9' tall triangle so that the cable made a 45* angle to it, holding off deflection would only require about (weight + 40%) tension... but you've got a little creek and you don't want the tension rod/cable to catch stuff that's floating in high water.
dodge man
Super Star Member
It MIGHT be ok for your tractor also but that’s above my pay grade.
Something else, and this is way over my head, but in design and on a lot of steel bridges the beams on one side sits on rollers and are not encased in the abutments. But I also have done construction staking where the beams are encased in the abutments. I’m not sure if you gain anything by letting one side being unrestrained or not.
Something else, and this is way over my head, but in design and on a lot of steel bridges the beams on one side sits on rollers and are not encased in the abutments. But I also have done construction staking where the beams are encased in the abutments. I’m not sure if you gain anything by letting one side being unrestrained or not.
AnotherBueller
Gold Member
White oak much stronger and out of ground contact will last longer. I you want it to really last do what truckers used to do, after the wood has dried a couple of years pour used motor oil on it. All those carcinogens put paid to bugs and the oil seals the surface really well.
