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RE: Upward load on slabs per UFC 4-023-03

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There is no good research for the millisecond blast load bracing dynamic effects in bending.  Intuitively it should not be a problem, but again it can not be quantified or computationally substantiated.  Most engineers will increase the section as opposed to adding bracing.  Increasing the section is cheaper.  Blast loading and uplift and progressive collapse studies are not that well understood at this time. 
 
There is research being conducted on wall assemblies with brick facade.  The brick mass absorbs a lot of energy, but it can not be quantified at this time to reduce superstructure blast loads.  The brick veneer is currently assumed sacrificial and has no special blast requirements. 

Regards, Harold Sprague






Subject: Upward load on slabs per UFC 4-023-03
Date: Thu, 20 Nov 2008 14:42:43 -0500
From: dwatt(--nospam--at)rubyusa.com
To: seaint(--nospam--at)seaint.org


I am working on a Corps of Engineers project that is required to resist progressive collapse. The project is a “Low Level of Protection” building that meets all setback requirements. I am unclear on how to interpret UFC 4-023-03 section 2-2.2 “Upward Loads on Floors and Slabs”. It states “In each bay and at all floors and the roof, the slab/floor system must be able to withstand a net upward load of a magnitude 1.0D+0.5L.” It goes on to say “Design the floor system in each bay and its connections to the beams, girders, columns, capitals, etc to carry this load.”

 

In the case of steel beams supporting concrete on metal deck I assume the concretes slab on metal deck will need to be designed for that upward pressure as well as its connection to the supporting structure. Where I am unclear is, are the floor beams required to be designed for the upward load applied to their tributary area with the bottom flange un-braced? If so, is bottom flange bridging typical provided to if reduce the beam section. Or does the upward load requirement only apply to the slab and its connections and not to the beams?

 

Also, is brick veneer on metal stud backup an allowable exterior wall construction for this type of project? All of the research I have found so far addresses the building structure and not so much the building envelope. Are there any special requirements to using brick veneer on metal stud for exterior walls on this type of project?

 

David M. Watt

 



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