E80 Railroad Concrete Box Culvert Design

[minorchord2000]

I have been tasked to design a single and double concrete box culvert with minimal overburden other than the minimum ballast thickness of about 1 foot. Can the 40 kip wheel loads (80 kip axle loads) be laterally and longitudinally distributed with such small overburden to get an equivalent uniform load? The clear culvert spans are approximately 10 feet.

 

[JLNJ]

I'm going to say "no".

 

[minorchord2000]

JLNJ: Thanks for your quick response. I suspected that there must be a minimum overburden beyond which distribution is permitted. In my case, should I just apply the wheel loads directly to the top of the culvert? If I am designing a 1 foot wide strip, do I use 4-40 kips loads at 5 ft spacing and move them across the culvert?

 

[bridgebuster]

First thing - get a copy of AREMA and look at Part 16. You'll see that the answers to your questions are: No & No.

 

[minorchord2000]

Bridgebuster:

I know the answer is within AREMA. It is just too damn expensive to buy at our small office. I thought someone could give me a simple answer. I'll just muddle through then.

 

[dhengr]

Minorchord:

You are suffering from problem we all seem to have these days, with small offices being hit hardest; and that is that you now need $400,000 worth of codes, manuals, and software to do $1000 worth of engineering these days. This doesn’t particularly improve our profession or our structures, but the publishers are getting rich. Can’t you beg, steal or borrow the AREMA manuals; a Uni. library or another consultant’s office library, they certainly are the place to look for the details.

Bridgebuster knows better than I do, but I would think the ties cause a distrib. of some width on either side of the rails, and the rails cause the wheel load to be distributed to several ties at a time, maybe with some adjustment at rail joints. I would think the AREMA methods would show something like this. Thus, you are talking about a moving 2'x3' +/- load area at 40k, not a point load. Maybe just design the top slab of the culvert with a normal thickness, but under the rails thicken it in an upward direction, an upset beam if you will.

 

[bridgebuster]

minorchord - you can still use an equivalent uniform load. However, the 1' of fill doesn't give you anything.

More important though, if you're designing a railroad bridge, how is it you're not using AREMA? (unless of course your client doesn't require it.)

 

[minorchord2000]

Thanks Dhengr and bridgebuster:

It is a two barrel concrete culvert with minimal cover. All the references I have allow a distribution based on overburden and the 5' longitudinal wheel spacing. I doubt the AREMA code permits such distribution when the cover is less than 18". All the examples I have have a nice cover of 4 or 5 feet.

 

[dhengr]

The 5' longi. distrib. undoubtedly has most to do with the axle spacing on a std. railcar truck for that 80k axle load, and total width distrib. will be a function of rail spacing, (4'-8.5") again about 5'. Then soil mechanics, depth of soil and soil properties come into play to arrive at the load on the deep culvert. But, your shallow ballast condition just will not allow this, so you are basically stuck with something like my 2'x3' moving load area. And, these area dimensions are a function of the relative stiffness of the grillage consisting of the ties and the rail as they relate to the rolling point load of 40k, and to the ballast stiffness, with a joint likely being the weak spot. I can’t imagine that AREMA won’t have some discussion on this issue.