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Metal stairs & story drift

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Our structural engineering firm provides engineering consulting for a
manufacturer of metal stairs.  We have not been able to find any part of the
building code (UBC) that specifically addresses the seismic design
requirements for stairs.  Our present concern is with the relative
seismic-induced motion of one floor to the floor above or below.  The
industry standard practice is to rigidly attach the stairs at each floor
We have noted Section 107.4 from the SEAOC "Recommended Lateral Force
Requirements and Commentary", 1996 edition , which addresses 1994 UBC
SS1630.4.  Is this paragraph intended to include stairs?
We also have specific questions from the 1997 UBC on this topic:
* Sections 1630.9 & 1630.10:  Are calculations required to show that stairs
can accommodate ?M for every stair?  Or is it only required to show that
stairs can accommodate ?M when the building's calculated story drift exceeds
0.025 times the story height (Section 1630.10.2 Exception 1)?
* Section 1632.4: Is this paragraph intended to include stairs?
* Section 1633.2.4: Is this paragraph intended to include stairs?
To summarize our question: When is it necessary to provide calculations and
special details to allow for story drift in stairs?  Are drift-allowing
connections only required where building deflections are unusually large or
does every stair that connects one floor level to the next need to have a
drift-allowing connection at one of the floor levels?  If drift-allowing
connections are required, do they need to allow for movement in all
directions or only parallel to the stringers?
We also welcome any other comments or observations you have about the
performance of steel stairs during seismic events.

Thank you,

Joseph Ward, E.I.T.

Leavitt & Associates Engineers, Inc.
1324 First Street South
Nampa, ID 83651
Phone (208) 463-0333 x12
Fax (208) 463-9040