This can't be right- an 80', W10x22 I-beam (W), holding a 100k truck? 7

[cdowling]

Hey Guys,

First time posting here because it's the first time I've ever had to solve this sort of problem. I have some land that we just bought that has a ravine blocking the entrance. I am designing/building a very simple beam bridge to cross the ravine that consists of 5 W-Type I-Beams, spaced about 3' apart, with both of their ends bolted to very large reinforced concrete abutments. The decking will be railroad ties (6"x9"x8.5' set end to end for a total deck width of 17 feet), with a simple butt joint over the center I-Beam and about a 2' overhang on either side of the outer most I-Beams.

One day, we will be building a house on the other side of the ravine, so I am trying to design the bridge so that a fully loaded concrete truck can cross-over. My reasearch indicates that this should be about 70,000lbs. I am using 100,000lbs just to give myself some margin.

So, in a furious pencil-whipping session tonight, I ran across this website:

http://www.engineersedge.com/beam_bending/calculators_protected/beam_deflection_2.htm

after entering in all the dimensions, I found that, suprisingly enough, a 80 foot long, 10" beam can single handedly support a fully-loaded concrete truck suspended by a cable at its midpoint, and only deflect a little over a quarter of an inch... Which was very exciting at first... but then pretty scary after I thought about it a little bit. Something doesn't seem right...

I used this website:

http://www.efunda.com/designstandards/beams/RolledSteelBeamsRltsW.cfm

for all of the dimensions and Moment of Inertia information. I also used 29,000,000 for the modulus of elasticity of structural steel.

So, does this seem right? I know I haven't accounted for the weight of the timbers, but I was just looking for a really rough estimate to get an idea on how much the materials are going to cost to build the bridge.

I've attached some very simple (cheesy) pictures to help show what I am trying to do. Please be advised that this is a 27" beam shown in the picture, but the calculations I ran were with the 10" as detailed above. This is just to give you a rough sketch of what I'm trying to do.

Thanks in advance for any advice,
Cody

 

[rb1957]

to find out more about designing a bridge consider ...

http://bridgecontest.usma.edu/

 

[JAE]

I'd second the comments of JStephen and rb1957.

What is your motivation for doing this yourself?

Saving money?

You save the fee of a structural engineer up front - and if you don't ever get a structural engineer to look at it I can almost guarantee you'll pay far more for your design than if they did it, either through excessive beam sizes or bad details that limit the life of the bridge and require higher maintenance costs later.

If you do try to show it to an engineer after you have "designed" it, they will most likely have to charge you the same fee to review/re-calculate the design anyway.

 

[vandede427]

I think you've got some bigger issues to consider than the size of the beam. Let's get away from talking about the design of the beam and talk about exactly how you're going to get these things in place over a ravine.

1. The availability of steel shapes/lengths from a supplier. They might have 60' or 80' stock lengths. They might have to shop splice the beams to obtain the lengths you need.
2. If they shop weld a splice, then you'll have to place that beam in one piece. Does your property have roadway access clear enough to get an 80' long piece of steel down it? Can you even ship something 80' long.
3. Does your property have roadway access for a crane to lift these pieces into place? If you have to field splice the beam, how will you do that?
4. Each beam will probably weigh 3 tons and be 80's long. The boom on that crane will be huge.

Think about how this will actually be done. You'll need plenty of access room for a crane and for these beams to sit on your property after delivery.

 

[Lion06]

I agree with JAE - I don't believe any engineer will look at your drawings/design and give you an ok without doing all the design checks that he would have done in the first place. This becomes even more true if you're asking him to sign and seal the drawings.

 

[hokie66]

I would look at a Bailey Bridge for your application. You might find one on ebay or somewhere. Not sure what the secondary market for Baileys is like, but there should be some surplus ones around.

 

[PSlem]

The length is ideal for a rail flatcar bridge.

 

[KootK]

You're clearly a bold and self reliant chap cdowling.

I say design yourself a cable stayed bridge using giant boulders for your tie backs. And forget about the railroad ties. Go for roman style pavers inlaid into an FRP reinforced concrete deck. Let's see any of your neighbors beat that.

Seriously though, I respect your tenacity in wanting to do this yourself. I'm the same way sometimes. I can never resist tinkering with my Mazda even though it invariably makes the final repairs more expensive.

 

[transmissiontowers]

I'm no bridge guy but I fired up my structural program and found that 5 W14x145 beams will support a 20 kip load each (1/5 of the total) in the center of a simply supported 80 foot span. The weight for 5 beams will be 58,000 pounds and at about $2 per pound, you are looking at $116,000 just to buy the beams then you have to get them installed and put the decking on them and install the abutments at the site. You may have $350,000 invested in crossing the ravine before you start building the house.

A simply supported beam is probably the least efficient way to span a ravine and you should probably get a real bridge structural engineer to design a cost effective bridge to span your 80 feet.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[cdowling]

Ok, ok. I give. Here is what's been happening since the last time I posted. It's sort of neat the way it worked out because each day I would learn something new from independent research and almost the same day someone on here would bring up the same topic. (Difficulty transporting beams that long, web buckling, supplier issues, cost of steel, etc. etc.) As one that enjoys learning, it was cool to have some issue brought up by reading your posts (or talking to local professionals) and then going off to read about those issues and how they can be avoided or solved.

To answer a few of y'all's question: "Why would you want to do it yourself?", the answer is primarily that I would have enjoyed the challenge and completing the task. Ostensibly, it would have been to save money, but truthfully I would have rather designed and built a bridge that cost more than a professionally designed bridge, just because I've never done it before- as long as I could be sure that it was safe (and I would have, had I chosen to build it).

In the end, what won out was cost. Of everything I considered, a bridge would be just too expensive. Since it would have been a DIY project to save cost (or so I would have told my wife), I would have wanted to do something that I could preform a majority of the work on. However, it would have boiled down to steel or concrete trusses or beams. Since I don't have the facilities or equipment to construct prestressed concrete beams, I would have had to farm that out, as well as having them placed, so that ruled that option out. I could have done all the welding myself, but the steel is prohibitively expensive for such a cost sensitive project.

One of the coolest ideas put forth was the bailey bridge. I did find some used units for sell, but if I were to have gone that route I think I would have spent the time to go back and research them and recreate a more permanent version myself for the project. I've been doing a ton of reading about them and that would seem like a very good option if I absolutely had to build a bridge over the ravine. Thanks for that suggestion.

The best of all options is an earth bridge (culverts) with retaining walls on either side to avoid the massive amount of fill dirt (an extra length of culvert) that would have been needed for the 4:1 ratio I would want to put on the upstream and downstream embankment. Since our property is bordered on one side by a dry creek that is in the flood plain, I'll need to have a hydraulic analysis performed and the culverts sized appropriately for compliance with the county's flood plain administrator. So, obviously, this part of the project is not "DIY" but I do intend to set the culverts, pour the apron and wingwalls, and build the retaining walls according to the engineer's drawings. That should scratch at least a little bit of that itch for me.

I'll post pictures when it is complete- hopefully 3-6 months.

Thanks for those of y'all who posted helpful and informative responses- I appreciated it.

Cody

 

[racookpe1978]

You have now discovered why the first Trans-continental railway got paid more for building through the mountains than across the sweeping plains! And also why the Central Pacific laid less rail mileage than the Union Pacific.

(Lay the culvert pies (or two or three) down, then rent a Bobcat to grade down the entrance/exit approaches into the 80 foot ravine: you'll lower the entry slopes, have more fill close by that you are pushing sideways rather than trucking in, and will make the rest of the road a bit easier.

Remember to install some sort of "side markers" - but probably not fully strong highway crash barriers or guard rails - for the causeway: at night, in storms or after snowfalls, you will want to know where the edge of the road is.

 

[racookpe1978]

Please understand an (empty) culvert pipe will usually transmit more water than a culvert pie. 8<)

 

[oldestguy]

How's come no one mentioned that you will need foundations on the side of a ravine? Not easy stuff.

 

[apriley]

Something that might work for you -

http://www.con-span.com/CON-SPAN/nof_main.html

They have nice-looking structures that are erected pretty quickly and easily. It might take away some of your "do it yourself" ability, but then again it might not be a bad solution.

 

[rb1957]

is there no way around the ravine, ie thru a neighbour's property, at least for the very loads for building your house ? if this was only for your long-term access (ie not for delivering building materials), you'd be looking at a much lighter load (10,000 lbs?) but the structure would need to be durable ... i like the idea of an culvert ... concrete pipe at the bottom (for water flow), a bull-dozer, and a 24 (or two) ... then you'd've something to put your raailroad ties on !

good luck, do let us know how it turns out !!

 

[cvg]

since you have decided to go the culvert route, don't forget your 404 permit...

 

[BSE05]

There definitely is a moral here somewhere.

Our aspiring bridge designer is obviously an intelligent and motivated engineer wanting to learn. But unfortunaltely bridge building is not like say gardening.

There are many reason why I don't do electrical engineering, although I had courses in college and can wire up a receptacle .... what could possibly go wrong if you don't do it right? Cause and explosion? Burn down the building? My point is that engineering for a bridge (or a culvert) is more than statics 101, just as electrical is more than E=IR.

The first thing to learn as any type of engineer is to know your limitations and when to seek help.

Well I feel better getting that out.

 

[petertor]

Back to the original question (!), drive three 12" HP piles to refusal, pour a concrete pile-pier, drive sheet pile and pour concrete abutments, then span the 80-foot ravine with (2) two railroad flat-car frames instead of fab/erecting one:

http://www.ctre.iastate.edu/pubs/t2summaries/flatcar-bridges.pdf

If the B.O./F.M. won't buy that 'cheat', buy RC hollow core prestressed slabs to span over the pier, and just tell the prestress plant what #-age AASHTO live load rating you want.
For private use you don't need a topping slab or guardrails.

If the ravine is that deep a center pier wouldn't work, you will need a geotechnical long before you need a structural.

 

[JAE]

For private use you don't need a topping slab or guardrails.

...until a visitor comes by for a chat, drives off your bridge and sues you for injuries. Then you'll need a guardrail.

 

[Dinosaur]

I just stopped in here for the first time in a few weeks and I find this little thing.

I designed bridges before I began supervising their construction. Your loading is close to the standard bridge loading called for in the code. Good for you thinking you need to support things like a concrete truck or a fire truck and not just your pickup truck.

I can tell you that for an 80 foot span, it is difficult getting even a W36 to work with a concrete slab helping in composite action. However, in your case you should be able to reduce the fatigue provisions, and that will help save some money.

A culvert is an economical solution to any crossing whenever the hydraulics allows that as an option. I suspect the hydraulics will dictate the final solution. If you need a bridge, there are companies that prefab truss bridges and ship them to your site. They are among the most economical bridge solution you will likely get. They will design the bridge for you. You could even contact them for an estimate, but you need the hydraulics issue settled before you get to that stage.

I recommend you get the hydraulics study done. If you can use a culvert, go that way. If you can't, contact a prefab truss manufacturer and talk to them. In the end, it will be more expensive than you ever imagined. Good Luck.

 

[Stillerz]

Get a good Four Wheel Drive Dodge and crossing the ravine will be a breeze...no need for a bridge or culvert.