Another bridge building question...

[cityboyturnedcountry]

Hi all....long time lurker, first time poster. I've seen lots of good ideas here and the answers to previous questions seem to be most in line with what we're looking to do, so here goes....

Long story short, need to build a bridge over a creek that's about 25 feet wide, and it needs to be built to accommodate cement trucks/lumber deliveries/etc. that go with building a house. Thinking that we'd set the piers further back on ground that doesn't often get fully saturated, I think we'll be looking at about a 32-35 foot clear span. Thanks to a wife whose uncle does DOT highway bridge building, I have 4 W33x118 beams ranging in length from 41' - 45' that I bought out of his scrap pile. Being a highway guy, he wants us to use concrete for the bridge. We'd rather go with something that matches the wooded area a little better.

If I had my way, the deck would be about 14' wide. I originally thought that the best way to start designing this was with two beams centered 8'6" apart so that they would bear the load of the commercial trucks, with the other two beams out further toward the edge. A friend who's a mechanical engineer said he would considered butting two beams up against one another, with the centers around that 8'6" mark. Not sure how much I like that idea in case we get a semi driver who veers off track, but maybe that's a moot point considering the decking.

I'm most intrigued by the idea of using 4x10s on edge as found in the post quoted below:

Anything about building bridges catches my eye. I have built a few--lots of fun. I am concerned about your proposed use of steel grating for a deck. If you build it correctly, the deck can actually add to the carrying capacity of the bridge. My biggest project was a 47' span using W24 x 180 beams 8' apart, and a 14' wide deck of 4 x 10 PT on edge. The 4 x 10s were spiked together every three ft using 12" spikes, so each spike went thru 3 beams. They didn't quantify the amount, but the engineers said that such a deck helps to spread the load. We put 100,000# log trucks over it, and it doesn't budge--over 1,000,000 board feet so far.

This idea appeals to me because we could easily build those deck sections off-site and transport them in, then place them and work our way across. Assuming I go with a 14' width, I also envision being able to use a 12'5" center section on every other segment or so where I'd bolt in 4x4s on each end....to which I would be able to bolt a wooden guardrail (probably 2x8 or 2x10) with boards on each side of the posts.

Before I take this design to an engineer, though, I'd like to be able to run some calculations on the weight capacity myself, but I can't find a good site that will give me these calculations for beams that big. I am also open to any and all suggestions on what might work given these beams. I already own them, and although they're overkill for something like this, I think their size opens up plenty of possibilities about how to build this bridge.

Thanks in advance for any help you can provide!

 

[MossRoad]

Welcome to TBN! :thumbsup:

 

[vtsnowedin]

:welcome: from Vermont. A structural steel manual is what you need. Might find one in a good library or your wife's uncle might have access to one. Do these beams have any gussets welded on them for bolting up cross diaphragms?

 

[Egon]

Your handling commercial vehicles?

A certified design is what you require. Making a guess for cement trucks just ain't right.

 

[LD1]

4 beams is overkill if you can come up with a good way to deck it. As for a program for the beams, download beamboy. Simple and handy. I just plugged in one of your beams, and with a 35' span, that beam will have no issues supporting 100,000 pounds point load right in the middle of the span. Deflection would be ~0.85. With a distributed load, roughly double that rating. and thats for ONLY 1 BEAM. You are talking about 4??

So now we talk about decking. If you only use 2 beams centered at 8'6", and each top flange of the beam is ~12", you will have a 7'6" span between the beams, and a ~2.5' span outside the beams. Each 4x10 would be capable of holding ~4000# load that is evenly distributed. But beyond that, calculating the decking gets more complicated than simple steel. Many different wood species and grades, many different ways to attach them all together, lower ratings for wet-service location, etc. Depending on how they are all tied together, instead of a bunch of individual 4x10's, you basically have a big 35' x 10" chunk of wood. That is where you will need to speak with a local engineer to see what is acceptable in your area. But I would think topping with 4x10's would be fine.

But no matter how strong you "think" you build, you still need to talk to an engineer and get his approval and an actual load rating. Without that, you may have a hard time convincing 80,000# concrete and delivery trucks to cross, as well as the fire department.

 

[EddieWalker]

You mentioned using piers to support the load of the bridge. I think you have a good plan for the bridge itself, but you need more then just piers at the ends. It's going to take a lot of concrete poured pretty deep into the ground to carry those kinds of loads. Figuring out how deep you need to go, along with all the other dimensions will require a local engineer familiar with your soil type.

Eddie

 

[rd_macgregor]

Am I understanding your plan right? Decking with 4X10's on edge would take a LOT of lumber; possibly 120 boards, if I'm calculating right. At about 163# per 14ft PT 4x10, this comes to a deck weight (without the spikes) of more than 3/4 ton. I bet it would be really strong, but assembling and positioning it might be a real back-breaking job. It is do-able, and you'd have a heck of a bridge deck when you were done, but I ache in sympathy just thinking about it!
Bob

 

[radioman]

Also 14 ft wide may or may not be wide enough. I am thinking of the truckers point of view sitting waaay up there in the seat driving over a narrow bridge with a full load.... like the cement truck. If you are so concerned about the looks of concrete, why not dye it brown before pouring? use wood for railing for woodsy look?

All I can think of is the IRT driving on the mountiainside roads and poorly built wooden bridges that looks iffy and you certainly dont want to mimic that.

 

[cityboyturnedcountry]

Thank you to all for your comments so far -- exactly why I joined!

I might not have been as clear as I should have been....this is not a "DIY by guessing" kind of job. I will certainly be having a local engineer do the planning and final calculations and tell me what I need -- but I was trying to do more of the design work myself and hopefully come up with a feasible idea instead of spending the engineer's time on design. I had downloaded BeamBoy and must have been doing something wrong because I wasn't having much luck in getting a deflection and/or weight rating, so I appreciate the calculation on my behalf. And "pier" was a poor choice of words, since I know that the abutments on which these beams will rest are going to have to be pretty heavy duty and will take a lot of cement to form.

I appreciate the comments and ideas -- always willing to hear more. I will continue to update as we get further along in the planning process.


Chris

 

[vtsnowedin]

Thank you to all for your comments so far ...
...And "pier" was a poor choice of words, since I know that the abutments on which these beams will rest are going to have to be pretty heavy duty and will take a lot of cement to form.

I appreciate the comments and ideas -- always willing to hear more. I will continue to update as we get further along in the planning process.


Chris

Nit picker here:ashamed:. Abutments are made out of "concrete" that comes in a truck and Cement is one part of that concrete that comes in a bag.
Rule of thumb. unless you're abutments are Way, way back from the stream bank the top of the footer should be four feet below the bottom of the stream.