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.

 

[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.

 

[LD1]

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

How far were you able to get with beamboy? Were you able to get the beam with supports and load drawn? I'll walk you through everything in any case.

1. when you open the program, you are prompted to choose a beam length. So I'll choose 35'
2. Now you have to select the features. At the top, second tab is features, then add feature, then add support. You need 2 supports. One at 0' from left edge, one at 36' from left edge.
3. Now add the load. this is also under features tab. You can have a point load, or distributed load. I choose point load of 100,000# at 18'. So a whole lot of weight, right at mid span.

4. Now select the I-beam properties you will be using. Beamboy has alot of info saved on common stuff. So go to the beam tab at the top, and select properties. Here you can manually input information, or click "choose" to select a beam they have in their system. After clicking "choose", select the W33x118 beam you have, then select "use x-x values". The y-y specs would be if you had the beam laying on its side.

Now that the beam is choosen, the final step is to calculate the stress and deflection. It is under the tab "calculate", then calculate stress and deflection. What pops up should look like this:


Beam deflection of 0.95" And a bending stress of 30,000psi. Since the steel is typically A-36 Which is 36000psi steel, you are under on stress, and deflection is usually not to exceed L/360. Where the length in inches is 432. So 432/360 is 1.2" max allowable deflection.

The beams are NOT going to be the weakest link. Using more realistic loading, lets say a set of tandems from an 80,000# dump truck or concrete truck. For a 36' bridge, the front axle is gonna be pretty muck off the bridge before the rears go on. So lets say this truck has 60k over the rear tandems. Which is 30k per axle, and 15k per side per axle. Assuming the axles are 4' apart, lets draw up a beam with two 15k point loads each 2' off center



That represents a more realistic loading. Here is what the stress and deflection look like



1/4" deflection when 1.2" is allowable. And only 8000psi bending stresses on 36ksi steel. Yea, the beams are fine. And like I said if you can work out the decking, I would not use all 4 beams. You can probably sell 2 of the beams to pay for the rest of the project.

ANd you can also use beamboy for wood beams too just so you know. When selecting beam properties, instead of hitting choose, select calculate. Input the wood dimensions and it will give you the i4 and distance to farthest fiber numbers. Then you have to change the modulus of elasticity to match whatever the lumber you are using. Steel is 30million. Wood is usually around 1 million. If you dont change that, and input your 4x10 dimensions, it will give a result as if it were 4x10 solid steel. You also have to know the max stress allowed in the wood. Where A36 steel is 36ksi, for wood the Fb is lower. usually between 500-1000psi for graded lumber. And up to and over 2k for MSR and engineered lumber

 

[Budweiser John]

Interesting post. Please keep the site posted with pictures of the work in progress and the finished bridge.

Just a couple additional thoughts. Do you need to have your state DNR involved for a permit? Local building jurisdiction? I hate buracurstery but better to be on the good side right from the get go.
Thinking about the concrete placement for the abutments. Sounds as if a concrete pumper may be necessary and that would add a significant amount to the project cost.

 

[rd_macgregor]

I have an old wooden bridge that will need replacement within the next few years (if mushrooms growing out of the deck suggest anything). My span and load requirements are a lot less than yours. I have been thinking in terms of repurposing a flat deck shipping container or trailer/truck bed. For supports at the ends, I've been thinking about having a local construction company drive two steel piles on each side with a steel beam welded across them to support the bridge ends. I wonder if this would be easier and/or less costly than a massive concrete abutment?
Bob

 

[vtsnowedin]

I have an old wooden bridge that will need replacement within the next few years (if mushrooms growing out of the deck suggest anything). My span and load requirements are a lot less than yours. I have been thinking in terms of repurposing a flat deck shipping container or trailer/truck bed. For supports at the ends, I've been thinking about having a local construction company drive two steel piles on each side with a steel beam welded across them to support the bridge ends. I wonder if this would be easier and/or less costly than a massive concrete abutment?
Bob

Current bids are running about $0.50 per pound in place and a 14x14 x1/2" pile runs 90 lbs./lf but that is on jobs where there a lot of pounds to drive per set up and mobilization. To drive just four piles they are going to want a good stiff fee just to bring the equipment there and set it up. A couple of 36" diameter concrete filled sonotubes set in ten foot deep augured holes might be cheaper and easier to do.

 

[Egon]

Isn't there a difference between static and dynamic loading?

 

[cityboyturnedcountry]

Holy moly, LD1 -- this fellow Buckeye thanks you for that wonderful tutorial! I truly appreciate it! I missed a few steps due to my unfamiliarity with it, and that makes all the difference.

Based on what these calculations are showing, I'm happy to read your assessment that the beams won't be the weakest link. And I somewhat agree with you that two beams should be enough, but with the way scrap prices are these days, it might not be that big of a hit to the wallet to just keep the extra two. At any rate, it's time for me to sharpen the pencil a little bit and spend some time with a structural engineering firm to figure out our best options.

Thank you so much to all for welcoming a newbie! Any and all ideas are still welcome....and certainly appreciated.

 

[s219]

Don't forget live loads for a bridge with vehicle traffic -- that is an important factor.

 

[aczlan]

How far were you able to get with beamboy? Were you able to get the beam with supports and load drawn? I'll walk you through everything in any case.

Thanks for the tutorial, it let me check how a beam I have would work for a cider press (very well) and how it would work for another location to help in the house

Aaron Z

 

[Egon]

Don't forget live loads for a bridge with vehicle traffic -- that is an important factor.

Aren't there also buckling considerations that are required?