Storm Shelter Debris Hazards 2

[KHoff]

I am working with a client who wants to place pre-engineered storm shelter units around his site. He is asking about concerns with locating storm shelters in close proximity to any buildings on the site and if the storm shelter could withstand debris impact forces from an adjacent building collapse. I know that shelters are designed for 100 psf roof live load, and the shell must pass the debris impact testing (2x4 fired at 100 mph), but I am not convinced that those requirements would cover the impact forces from a 40 foot tall precast wall falling on the shelter.

Are there any references or resources that could provide some insight on this issue? ICC 500 is pretty vague, stating the following:

305.3 Other debris hazards.
Lay down, rollover and collapse hazards shall be considered by the design professional when determining the location of shelters on the site.

It seems like the best option might be to place the shelters far enough away from buildings that a collapse will not impact the shelter, but I'm not sure that is feasible on this site. Also, it's not clear exactly what that distance is. For example, I wouldn't necessarily expect a 30 foot tall CMU wall to just lay down intact and impact the ground 30 feet from the building. But I suppose its not impossible.

Clearly this is a messy topic. Any insight would be much appreciated.

 

[phamENG]

Messy - very messy. I'd start by determining a "design missile" or piece of debris. Once you know the mass and probable height from which it will fall, you can work out its potential or kinetic energy (depending on the impetus of its movement). Determine your stress/strain curve based on the design of the shelter, and then you can determine the material stress that corresponds to the level of strain energy required to elastically resist the potential energy from your falling debris. There are lots of assumptions that have to be made, so be conservative.

You mentioned it's pre-engineered. Does the manufacturer offer any clues or test reports? Seems like missile debris hazards would be a good evaluation topic for such a product.

 

[JAE]

ICC 500 is pretty vague

This tells you that there aren't many (any?) references or resources available.

The force from impact is almost impossible to predict under any probabilistic framework (i.e. - no way to get a rational safety factor or even range of load) from falling debris.



Check out Eng-Tips Forum's Policies here:
faq731-376

 

[KHoff]

I have not asked the manufacturer about this yet. I am guessing they only have data on the shelter passing the 2x missile tests.

 

[caenright]

The de facto standard for collapse hazard area for structures as applied by the fire service for disaster/fire environments is assumed to be 1.25 or 1.5 times the height of the building.

The US Army Corps of Engineers USAR Structures Specialist Field Operations Guide (attached) may be a good resource for information on anticipated collapse behavior post-disaster and contains this assumed distance for collapse zone. There are other good references at

http://disasterengineer.org/

that may be useful for this sort of design work.

 

[KHoff]

Thanks ca_enright, that is very helpful.

 

[BouncedPod]

FEMA 361 may also be able to give you some guidance.

 

[JStephen]

I would think if you got it too far from the main building, nobody would use it either- if you have a thunderstorm and driving rain, running 100 yards to a storm shelter doesn't sound too inviting, either.