roof design for blast load

[newdnbea]

here i have some questions about roof design for blast load.

we are going to frame the roof using steel beams and girders with steel deck and concrete topping.

the first question is about the deck. are there any type of composite deck intended for blast load?

the second is about the beam and slab connection. the roof beams shall be connected to the slab to prevent separation during rebound. is there anyway that we can design the connection to prevent the composite action between the beam and the slab?

thanks.

 

[MiketheEngineer]

What kind of blast load - internal or external??

Many roofs are designed to blow away from an internal blast load.

If this external - what kind of over pressures are you looking at?

This question has been discussed in these forums a few times. You might want to a "search"...

 

[newdnbea]

external. of course the the overpressure is big enough for me to do a dynamic analysis. say it is 6 psi.

I did a search this morning but didnt find what i need. maybe i will do a search again.

 

[MiketheEngineer]

That is on the order of 865 psf!!! I know the DoD and Homeland Security have studied this.

You are out of my league.

 

[Gumpmaster]

Why do you want to prevent composite action between the slab and the beam? If anything, just ignore it, it only helps.

If you run a single degree of freedom dynamic analysis, then your loads will be greatly reduced (or mitigated by plastic deformation at least).

Is this something that's meant to be operable after a blast, or just not collapse?

Check Out UFC 3-340-02 on WBDG.org

 

[MiketheEngineer]

What about the walls???

 

[ishvaaag]

On composite "deck" against blast ... I am still to examine the literature on blast I have, yet it is clear that using a layered setup is a device of protection of inner spaces against both blast, projectile and direct weapon impact. The idea is to protect the inner layers where the outer layers exert a shielding effect to the inner ones, and being upon the instance blast loading discardable entirely or in part.

This makes me think that interposing some foam/frangible/weaker layer between an outer shielding layer and the deck can be conducive to
1. Damp blast effects and diminish rebound consequences.
2. Isolate the concrete outer layer from composite action with the main inner structure.

Reinforcing to some extent the frangible/discardable layer will lead to longer life of the shielding intent.

So I would start to explore along these lines.

 

[newdnbea]

to gumpmaster

i dont think it is going to help. when you use SDF method to design the member, the reaction of the supported member will be used as the load of the supporting member.

say you ignore the composite action of the beam and you get the reaction of 10 kips for the beam and you will take this 10 kips as the load to design your column. but the real reaction of the beam is say 15 kips due to the composite action. your column is underdesigned.

of course the dynamice reaction is a force time function instead of a 10 kips or 15 kips force. just try to make it simple.