FEMA Storm Shelter Debris Hazards

[sidneyrenee28]

I am designing a FEMA storm shelter. Concerns of "lay-down" (per ICC 305.3 below) of closely spaced elements has been brought to my attention. The shelter is located at a baseball park where field light poles, parking light poles and foul poles all pose a "lay-down" threat. I know the weights, heights and locations of the elements. Is there an impact factor or factor of safety that I need to use in conjunction with my weight to get my design force? Do I need to consider the acceleration of the element laying over due to wind (F=ma)?

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.

Any design method insight would be greatly appreciated.

 

[RPMG]

Theoretically, one would use the impact form to determine the force, F = m * dv/dt, but the time, dt, that the pole decelerates while hitting your structure is unknown. I think it's more practical to just choose a large impact factor. An impact factor for a rigid structure, like precast, will be higher than a flexible structure, like wood, which makes sense if you think in terms of deformation and dv/dt. As NASA said while firing chickens at glass, "Thaw the chickens." It matters.

There is also code somewhere that says that the shell must be able to withstand a 2x4 missile strike. Those assemblies are tested, like fire rated assemblies.

 

[TLHS]

An impact factor isn't a good way to deal with an actual falling load. They're more suitable for 'sudden loading' where a short drop or a quick load without a lot of acceleration will happen. If there's a lot of kinetic energy behind something, you can't really say the result going to be some multiple of the dead load.

 

[r13]

Locate the shelter in the basement, and make sure the building can stand on the storm, that the fallen structures/debris wouldn't fully pile up on the entrance of the shelter. More than one entrance will be ideal.