spiral stairs
spiral stairs
(OP)
I am in the procerss of designing a spiral stair and I do not know how to calculate the moment on the spiral column.
What are the load consideration? I am assuming all the load on one side thinking of people liningto the same side.
Do you have any ideas or suggestions?
What are the load consideration? I am assuming all the load on one side thinking of people liningto the same side.
Do you have any ideas or suggestions?






RE: spiral stairs
Carl Bauer
www.bauerconsultbotswana.com
RE: spiral stairs
If made of reinforced concrete it will be somewhat (but not completely) insensitive to eccentricity of load coming from the use of the stair. For a steel central member under the steps better model the steps as cantilevers directly.
The stairs made spiral as cantilevers from a central column are even more directly modelizable.
RE: spiral stairs
It is a steel stair free standing for two landings. The owner does not want the stair attached on the 2nd and 3rd floors landings. In the architectural drawings the architect is proposing a 5" circular column, that based on the loads per step it will be enough as per the aisc manual.
I am treating it as single cantilivered steps. But my real question is: When the stair is in full use, that would be a full evacuation of the building, I am assuming one person per step, we are creating 28 small simultaneous moments that as Carlbauer in his post said we could consider 1KN per step. How will be the column designed?
Another consideration would be having people standing on just one side of the stair, creating a similar moment that would be aplied on the column at the steps intervals, forcing some sort of buckling stresses on the steel column.
Again, any ideas?
RE: spiral stairs
After P-Delta with the if necessary reductions on axial and bending stiffness taken unto account, you can use directly the forces got for design without further amplification in one strength of materials approach if you dismiss the in-member out of alignment, which is normally safe enough given the scarce magnification resulting when the segments are short, or you use the equations in chapter H of LRFD with K=1 and non-sway since after such P-Delta Analysis the ends of the segments have been brought to a stable position and such ends can be assumed linearly fixed.
RE: spiral stairs
Pandeo de Estructuras
Felix Escrig
Publicaciones de la Universidad de Sevilla
QuUotes ELASTIC critical loads for columns
For a double pinned colum with uniform distributed load along the colum
Case II.15 at p. 56
where the forces keep orientation after buckling (gravity)
gives a critical load 1.88pi^2EI/L^2 or
K=1/1.88=0.53
Some accounted inelasticity (maybe on account of loss of stiffness cause spanish code NBE EA-95 a bigger value for K
from the formulation in Table 3.2.4.5 the same case gives K=0.729, which should be a more proper value for of K for your case since from a code, more conservative, and presumably accounting about phenomena that mere elastic buckling factor cares not.
If you provide some fixity at the base both references can guide you to lower Ks.
RE: spiral stairs