Pier Stem With High Moments
Pier Stem With High Moments
(OP)
Say I have a spread footing with a relatively tall pier stem or pedestal with very little axial load and very high biaxial bending moments.
Would it be reasonable to simply design this pier stem as a cantilever beam with biaxial moments?
Finding literature on this has been difficult. The minimal axial load and high moments all but eliminate using interaction diagrams....this simply doesn't fit the bill.
Would it be reasonable to simply design this pier stem as a cantilever beam with biaxial moments?
Finding literature on this has been difficult. The minimal axial load and high moments all but eliminate using interaction diagrams....this simply doesn't fit the bill.






RE: Pier Stem With High Moments
RE: Pier Stem With High Moments
That being said, PCA Column handles biaxial moments and axial load pretty well.
RE: Pier Stem With High Moments
I guess I am not really following you on the "Phi" part of your reply.
Care to inform me
RE: Pier Stem With High Moments
http://www.yakpol.net/ShortCol.html
RE: Pier Stem With High Moments
RE: Pier Stem With High Moments
When a beam is subjected to biaxial moments the following approximate interaction equation may be used for design purposes:
Mx/Mux + My/Muy <1.0
Which we have all seen before...
The text goes on to say that the this may be applied to axially loaded members provided that the axial load is no more than 15% of the column capacity of the member.
Would you feel comfortable with this?
RE: Pier Stem With High Moments
have you used this spreadsheet?
RE: Pier Stem With High Moments
RE: Pier Stem With High Moments
RE: Pier Stem With High Moments
For columns, φ = 0.65 while for beams it is 0.90. As your axial approaches zero, ACI allow the "column" φ to change over to a "beam" φ.
RE: Pier Stem With High Moments
I would design it as a beam. If the pedastal is circular then there would be no need to Mx/φMux + My/φMuy <1.0. You could resolve the bi-axial moment and solve for M/φM <1.0.
RE: Pier Stem With High Moments
There is so little axial load (relatively)that I just couldn't see applying any interaction to the design at all.
The pedestal is square and I have designed it as a biaxial beam. I wanted to make it round just for the reason that you state Asixth, but owner says no.
Thanks for the feedback.