foundation design - need quick answer

[broncosfan]

This question is probably answerable by someone familar with bridge design, but the AREMA design manual for train structures indicates that impact loads are not normally considered for foundation design. Does that include reinforcement or are they just referring to stability issues (such as bearing pressure and overturning)?

 

[JStephen]

"include reinforcement" = foundation design
"bearing pressure and overturning" = foundation sizing
That's the distinction I'd make- don't know anything about the standard in question, though.

 

[JEmH]

I'm also not familiar with the standard in question, but I am familiar with AASHTO LRFD Bridge Design Specifications which says (in 3.6.2.1 2nd bullet) the impact factor "need not be applied to foundation components that are entirely below grade level." Some state DOTs clarify that to mean that abutment stems and footings do not get the impact factor but pier caps and shafts do. I realize that I haven't exactly answered your question, but I will note that I know of no standard that makes the distinction of applying the dynamic load allowance to a foundation for one aspect of design but not another. I imagine if this duality were the case with the rail standard that it would explicitly stated. Hope that helps.

 

[jimaitken]

Although I am not entirely familiar with AREMA, I would interpret their meaning to be for both stability and reinforcing design. As JEmH said foundation components entirely below grade are generally designed for factored loads, but impact is typically not considered.
Note though that AREMA does indicate that you DO have to consider vibratory effects in your footing design. Depending on you structure this could be more a more serious consideration than an increase of the live load by a certain percentage.