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RE: Metal stairs & story drift

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Mr Ward

I believe that a better code provision is Section 1631.2.4 (1994 UBC since
my 97 copy is at the office) which states "All framing elements not
required by the design to be a part of the lateral-force-resisting system
shall be investigated and shown to be adequate for vertical load-carrying
capacity when displaced 3(Rw/8) times the displacements resulting from the
required lateral forces."  The 97 UBC should be slightly different but
having the same effect.

It is the  intent of the code that these provisions apply to stairs
regardless of the drift of the building.  The code provision applies to
drifts in any direction.  You can accomodate the movement by a slip joint
or by means of some ductile detailing that will deform but not fail.

There have been reports of damage to stair framing as a result of an
earthquake.

Remember that code provisions are minimums.  In any case you should design
all elements for the expected forces and displacements that those elements
will see.  


Mark Gilligan


++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 
It seems a bit of a stretch to apply rules for concrete columns to metal
stairs.  Anyway, we are curious to know how you detail concrete stairs to
accommodate delta-M, and would welcome a sample detail at fax number (208)
463-7670.

Thank you,
Joseph Ward