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pipe bridge
my firm is designing a pipe bridge crossing a railroad and a local road. will the aashto bridge code apply in this situation? i am confident in past projects (mostly in plants) the code was not used. simply lrfd or asd. i would feel much more comfortable using the code and feel it is necessary. what do you folks think??
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this is outside my area of expertise, but i agree that aashto should be considered since you are crossing a road. i would contact the owners of both the road and the railroad and find out what their requirements are, and make sure they're ok with what you're doing. you probably need to make sure that your design is conformance with the various clearances and other geometric guidelines in aashto. the same would hold true for whatever agency governs the design of railways.
if you were not crossing a road or a railroad or anyone else's right-of-way, then i don't think aashto would apply, and i would design based on the local building code using aisc iof steel.
i designed a sizable pipe bridge for my employer (on my employer's property), over a railroad about 9 years ago.
used only asd, railway company furnished clearance requirements, and engineering judgment. then applied my pe seal to the documents. before construction, plans were reviewed and accepted by the railroad company without comment.
that seems to be what has been done in the past. i'm an eit so i will not be stamping the drawings, however i want to be sure we're on the right path regardless. i think i will likely e-mail the railroad and the city and have a "paper trail" of our conversations to ensure they received what they asked for and we gave them such.
aashto provisions are cover (non rail and air) transportation projects. load and resistance factors, impact and distribution factors, and fatigue provisions are are developed with truck load in mind. there is an uncertainty about truck load and distribution that you don't have here. while technically, you're transporting something, i don't believe it is necessary to meet aashto for this project. i would try to find a code that is more specific to the application.
good call on the truck loading.
i agree with sre. i have been involved with several pipe bridge projects in ohio. we used building code loadings, aisc allowables, and engineering judgement. the county set the limits on the clearances. the one that was actually constructed was over a two lane road. we bid on several others including a multi-span over a road and a railroad. the only thing specified was vertical and horizontal clearances. i would think that you are going to have to think out of the box on this one anyway. the d/t limits set by aisc will require you to use a pretty thick wall on the pipe, much more than is probably required for stress and buckling. neglecting that limit and using shell theory for design will yield a much more economical design.
i agree that you wouldn't need aashto to size your structure. however, you do need to worry about making sure you have enough clearance between the bottom of your structure and the roadway, and you'll need to make sure that your supports are far enough away from the edge of the road. aashto might be a good place to look for these geometric requirements, and the owners of the road and railway should also be asked.
if you are crossing right of way owned by the railroad and a municipality or dot with active traffic you need to design to the owner's requirements. aashto and/or arema may still apply. aashto and arema have sections that contain the factors and load cases required for design. coordinate with you state dot and with the railroad to ensure that the code you are using conforms with what they require.
you should also check with your state dot requirements for vertical and horizontal clearances needed. each should be able to provide you with the required vertical and horizontal clearances that are necessary.
in my experience the railroad usually has fairly restrictive requirements when it comes to building over active tracks. they will also most likely limit construction activities so you should coordinate with them early to see what they will allow.
thanks a lot folks.... eng-tips is an incredible resource of knowledge.
check with the american railway engineering association (area, formerly arema) for your clearances. as stated above, you'd check aashto for your clearances over and beside the road. other than the requirements for barricades to protect errant cars from demolishing themselves on your bents, i don't see what aashto can do for you that lrfd can't. don't use asd, though. aastho has gone with lrfd for a long time because of the high dead load to live load ratio of bridges. if you are unfamiliar with lrfd, i would then suggest you use aashto for everything except your loadings.

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