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Foundation design for blast loads

Foundation design for blast loads

Foundation design for blast loads

(OP)
How do I handle blast loads for designing the foundation for a prefab building. The magnitudes of the load is way much larger than the conventional loading but the duration is in mili seconds. Does it mean the forces discipates before the foundation experiences them? Is there any guide lines to handle the blast loads for foundation design?

RE: Foundation design for blast loads

This is its own sub-specialty and in my experience the blast consultants are not quick to provide actual loading to use. That's because, as you say, the loads are off the charts; no building can be built to withstand those magnitudes of forces. At which point there are mitigation methods such as berms and barriers to redirect the blast, and the like.

The short version is that stand-off distance is your friend and absent that it becomes a bit of a black art, as near as I can tell. My suggestion is that if you're the structural engineer stick to designing the building and (subtly) force the hand of the blast consultant; have him tell you what forces to design to. Conversely, if you're the blast consultant, advise the structural engineer as to what forces to design to and don't try to design the building components. But whichever your role, don't try to do both. That way there are clear delineations of responsibility.

That's my opinion only, based off of knowing that I don't understand blast forces.

RE: Foundation design for blast loads

Boo1,

Thanks for the links. But, I have to say, wow...

The Navfac one was close to 2,000 pages of mostly theory, though it did include some design examples. It seems like they provide various loading charts making reference to blast-specific terminology that I don't understand and then provide various material over-strength factors based on it's short-term loading, as near as I can figure. That's a lot to absorb and yet, at the end of the day someone has to issue drawings for construction that have to be build-able with the minimum number of change orders. So, to piggy-back off of a thread from yesterday it seems that we as engineers are expected to be able to understand and stuff like that and yet schools don't teach students fundamentals such as typical stud spacing. Are we losing sight of the forest for the trees?

I think maybe I'll resign myself to designing tool sheds, dog houses, out houses, and the like. Until people decide to start blowing up those structures too...

RE: Foundation design for blast loads

taken from asce blast design:


Foundations are typically designed for the peak reactions obtained from the superstructure dynamic analysis. These reactions are treated as static loads, disregarding any time phase relationship.................................

RE: Foundation design for blast loads

(OP)
Thank you all for response. The foundation in question is for a pre-fab building the will house control valves and instrumentation for industrial plant. The blast load will be from shack waves from an accident in the plant.
Thanks "delagina" . I will check with the blast consultant whether the foundaion loads are from dynamic analysis.

RE: Foundation design for blast loads

If it's from a blast from within then I think the only thing that will mitigate that are blast vents; the force simply can't be "contained" absent putting it deep underground or something of the like. Perhaps one of the listed resources addresses that more specifically?

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