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NFPA 221 tied-firewall multiple bay

Question asked by sbeard on Mar 10, 2020
Latest reply on Mar 10, 2020 by milt.werner

NFPA 221 gives an option for a tied-fire wall (sect 6.4).  Rather than having the fire side super structure release and fall away, leaving the wall intact;  the superstructure is tied across the wall, and lateral bracing provided on non-fire side, so that when the fire side collapses, the wall can resist the catenary forces from the collapsed portion of the building despite still being attached.   It can be useful in high seismic areas where buildings need to be tied together.


Section says that non-fire side must be braced to resist the maximum lateral pull that can be develop from the collapse. 

The formula for the force (eq A.5.4) grammatically uses the singular from when describing the length of the collapsing beam,

Unfortunately, the illustration only show a single bay building.


Is the length of the collapsed beam (or sum of beams), the all the perpendicular beams from wall to edge of building? or is it just the length of the first bay?

This may be a question of whether during failure multiple beams sag, or whether the first bay from the wall sags all the way to the slab with the beams further away fully laying on the slab.