Wooden Bridge Question

[Diggin It]

This sounds more like a high school homework question.

 

[Jw5875]

Well after several years of bridge washouts, finally bit the
big one and called in the pro's for the abutments, the rest I
finished myself.
A fellow TBN'r was gracious enough to give me an
APPROXIMATE capacity for my bridge after seeing my
beams etc. No I won't the numbers.
Any how, age 72 and less concern for washouts now.
If this one goes, going to buy a Duck Boat!!!!!!
Built railing from well pipe.

JW5875

 

[airbiscuit]

Now we're talkin.

 

[kenmbz]

That looks really sturdy jw

 

[fried1765]

Well after several years of bridge washouts, finally bit the
big one and called in the pro's for the abutments, the rest I
finished myself.
A fellow TBN'r was gracious enough to give me an
APPROXIMATE capacity for my bridge after seeing my
beams etc. No I won't the numbers.
Any how, age 72 and less concern for washouts now.
If this one goes, going to buy a Duck Boat!!!!!!
Built railing from well pipe.

JW5875

It does look sturdy, but I would be very concerned about washout/erosion over time, under those big blocks, unless there is actually a deep concrete footing under the blocks, or another row of buried blocks, beneath those that are visible.

 

[IH3444]

Nice job, keep an eye on it for scouring. When you neck water down during flood stage the force of the water can cause scouring under your concrete abutments. Also the water flowing lower during flood stage moves faster than the surface water due to it being under pressure from the top water. It looks to be flowing smooth and nice, but the real work is going on under the surface. The deep the water, the more force it has to remove material. You are channeling the water into a narrower configuration, making it a more powerful force down below.

Chapter 2 - Abutment Forms and Scour | Countermeasures to Protect Bridge Abutments from Scour | The National Academies Press

https://mtri.org/mdot_scour_workshop/13_Swartz_ScourCountermeasures_2017.pdf

 

[deezler]

^ I too would be nervous about scouring under those big concrete blocks. From the pics it looks like the span of the bridge should be about 8-10' wider....

If you choke off the creek into a narrow bridge crossing, the next flood is going to be exerting tremendous pressure on those blocks and pulling material out from beneath and around them. Hope I am wrong and it holds up forever, but I'd be mentally prepared to do that whole job again someday.

 

[workinonit]

It's obvious to me that I don't know crap about building a bridge. It sure looks good for the long haul to me. What size I beams did you use for the weight baring load? And how much weight do you calculate it will hold? I need to build one but just to cross a ditch. I hate using tile for a crossing. All of mine need to be replaced now. They are full of mud or collapsed.

 

[fried1765]

It's obvious to me that I don't know crap about building a bridge. It sure looks good for the long haul to me. What size I beams did you use for the weight baring load? And how much weight do you calculate it will hold? I need to build one but just to cross a ditch. I hate using tile for a crossing. All of mine need to be replaced now. They are full of mud or collapsed.

My Civil Engineering training, with reference to the bridge in question, leads me to believe that your first sentence may be essentially correct.

 

[workinonit]

It is or I wouldn't have stated it. But thanks for confirming. It's pretty much why I don't build bridges and chose the EE route to repair and commission generator voltage regulators in order to keep your lights burning. The abutments aside I was really more interested in the actual bridge span structure. I assume since you guys didn't flame his butt over that it must be fairly sound. Thus my questions about the I beams.

 

[fried1765]

It is or I wouldn't have stated it. But thanks for confirming. It's pretty much why I don't build bridges and chose the EE route to repair and commission generator voltage regulators in order to keep your lights burning. The abutments aside I was really more interested in the actual bridge span structure. I assume since you guys didn't flame his butt over that it must be fairly sound. Thus my questions about the I beams.

There is not much to be said about the I beams, without knowing the web and the flange dimensions, and wt. per ft., other than that they do look like I beams!
Not all I beams are created equally!

 

[Jw5875]

The creek bed is almost solid rock, back fill was with large boulders
and stone. We widened the creek 4' under the bridge and it is 2' higher
than the previous span. Also there are headwalls on both sides on the up stream
side. We discussed possible erosion, but this flooding is not a constant problem.
Had several Tri-axles loaded with gravel for the other side,
bridge never flexed!!!!!!

 

[Renze]

Allways interesting to read these topics. People ask questions in a way of which you know they dont know whats important, (So its good that they ask) Then other people think they can give a definitive answer to that question, thereby showing that they have even less insight than the ones who ask.

The engineers who actually know whats involved in structural engineering, rather not get involved in these types of discussions because they know they cant give a conscientous answer without knowing all the variables.

I am not a civil engineer, but the water council approved my building permit calculation over a 40 foot span, because i calculated with the worst case scenario, the retaining wall T elements used have an extremely low ground pressure and are dug below the depth of the canal so washout is impossible. I reverse engineered the retaining walls certified side load into a bending moment, to find what these would support vertically. As deck we used 12 I beams 40 inch high, because we could get them used as a package deal. I ended up with a 120 ton static capacity, and let the authorities decide if this met the civil engineering code, because there is no information online because most people dont build their own bridges...

The bridge should support a 4 inline wheel slurry tank with 20 ton pendle axle load, and a transport tanker with 50 ton combined weight.

 

[rbstern]

The creek bed is almost solid rock, back fill was with large boulders
and stone. We widened the creek 4' under the bridge and it is 2' higher
than the previous span. Also there are headwalls on both sides on the up stream
side. We discussed possible erosion, but this flooding is not a constant problem.
Had several Tri-axles loaded with gravel for the other side,
bridge never flexed!!!!!!

Nice bridge!

 

[lostcause]

so the OP never got back with any info did they?

 

[workinonit]

Post #32

 

[MoKelly]

Post #32

Post #32 isn’t the OP. That is another bridge mentioned.

MoKelly

 

[deezler]

The creek bed is almost solid rock, back fill was with large boulders
and stone. We widened the creek 4' under the bridge and it is 2' higher
than the previous span. Also there are headwalls on both sides on the up stream
side. We discussed possible erosion, but this flooding is not a constant problem.

Awesome, thank you for the additional context and pics. I like the big boulders in front of the wing walls.
Dang, looks like your piece of land might just be a giant boulder pile with a light glaze of topsoil, LOL.

 

[Diggin It]

so the OP never got back with any info did they?

Well, since it wasn't a legitimate question, I don't expect them to.