P-Delta Effects
P-Delta Effects
(OP)
Anyone have any documentation on simplified approaches to P-Delta effects, particularly with respect to 3 or 4 story wood framed buildings. (I am hoping for a simplified approach or a document that explains the pseudo load approach better)






RE: P-Delta Effects
P-big delta effects are typically more of a concern in moment frames. P-little delta effects should always be investigated, but this isn't dependent on number of stories or lateral system.
I'll be interested to hear others' opinions on this.
RE: P-Delta Effects
I don't think it can be simpler than that.
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: P-Delta Effects
1) The seismic chapter in ASCE-7 has a simplified method. Section 12.8.7.
2) There is also the B1-B2 method that AISC gives. That's given in section C2.1b (of the 13th edition - Black book). The B1 is intended for moment frames and would probably be taken as insignificant for a shear wall system. Therefore, you'd just use the B2 method.
In addition, there is a good chapter in the 2nd edition of the Seismic design handbook (Farzad Naiem)
RE: P-Delta Effects
the way i understand it you can do pdelta 2 ways.. one using moment magnification B1-B2 method.. two using rigorous pdelta analysis done by FEM softwares..
RE: P-Delta Effects
Also, you have to be careful with the P-delta button. Most only do P-big delta, not P-little delta, so in order to capture the member second order effects you need to break the members you're concerned about into 4 (or so) parts.
RE: P-Delta Effects
RE: P-Delta Effects
RE: P-Delta Effects
If you are designing with the NDS, this is already accounted for in the Combined Bending and Axial Compression equation(Eq 3.9-3).
The terms account for this are the [1-(fc/Fce1)] and 1-[1-(fc/Fce2)-(fb1/Fbe)^2]. That takes care of the member second order effects. It's on page 20 in the '05 NDS.
RE: P-Delta Effects
Sort of an academic point, though. When you're talking about a shear wall structure, the story drift effect should be small.
RE: P-Delta Effects
That's correct regarding P-little delta. I noted that in the post.
I would also hold that the story drift effects are not relevant for an individual stud. I say that for this reason. A single stud, even in a shearwall, is pin-pin member. Even if the stud is differentially displaced by some amount at the top and bottom, it still is only seeing axial load from the floor above. That axial load might be somewhat skewed now in order to follow the longitudinal axis of the stud, but it's still an axial force only. The P-small delta effects are a result of the out-of-plane wind load against the wall. The P-big delta effects are on the shearwall as a whole, not on an individual stud.
RE: P-Delta Effects