P-Delta Question
P-Delta Question
(OP)
Basic question...
If using P-Delta analysis for a secondary analysis is the general rule of thumb that the P-Delta effects only need to be accounted for in the Lateral Force Resisting System (LFRS)?
In other words, secondary members like girts, purlins, or infill beams that are "along for the ride" don't need to be considered in a secondary analysis do they?
My issue is not exactly this straight forward, but....
If using P-Delta analysis for a secondary analysis is the general rule of thumb that the P-Delta effects only need to be accounted for in the Lateral Force Resisting System (LFRS)?
In other words, secondary members like girts, purlins, or infill beams that are "along for the ride" don't need to be considered in a secondary analysis do they?
My issue is not exactly this straight forward, but....






RE: P-Delta Question
RE: P-Delta Question
I don't think that is true if the beams or purlins that take gravity and lateral loads are part of a frame that sees additional lateral deflection due to P-Delta effects.
Othwewise, I would tend to agree.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: P-Delta Question
Seems ridiculous.
RE: P-Delta Question
I have been designing grits and purlins for a long time and never considered them in the second order analysis. This is assuming that the grits and purlins are not carrying compressive forces that would have any effect on the stability of the system (i.e. only used as beams spanning from main member to main member)
RE: P-Delta Question
RE: P-Delta Question
BA
RE: P-Delta Question
RE: P-Delta Question
RE: P-Delta Question
For various reasons the structure is not perfectly symmetrical. As a result, there is some differential lateral deflections in the model that results in bending of the purlins, primarily weak axis bending. A P-Delta analysis exacerbates the problem. I plan to stiffen the frames so as to mitigate this "secondary" effect but this all got me wondering if it was legitimate to ignore these "secondary" effects in the purlins. Hell, a few years back, I would have designed the frames and purlins independently and not take the interaction into account anyway! I realize that as a structural system this is a real phenomena, but I am not sure if it is necessary to go this far.
RE: P-Delta Question