Michael Bryson wrote:
<<If I could get some opinions:
Would you use Fp to determine seismic forces?
Would you consider the stringers as laterally braced by the treads/risers
for bending? for axial load?>>
I'm not sure what you mean by designing stairs for seismic forces. I guess
that I think of them as just another piece of dead load which is tied in to
the main lateral system. Are you using the stairs as some type of brace?
For gravity load I normally assume that the treads provide bracing to the
stringers against lateral-torsional buckling and make sure to detail a
decent connection of the tread to the stringers.
I can't recall looking at a stair to resist axial load but if I did I would
be leery of assuming that treads would provide bracing. It seems to me that
the stringers could buckle parallel to one another and the treads would not
provide any significant resistance.
Fp as per section 1632 of UBC 97 would be appropriate to design the stairs
themselves and particularly their connection to the main lateral force