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Nonlinear Plane Frame Analysis

Nonlinear Plane Frame Analysis

Nonlinear Plane Frame Analysis

Note: I already posted this in "Structural Engineeringa and Other Technical Topics" Forum but I thought people in this forum might be more likely to have knowledge of this:

I am attempting to program a second order (geometrically nonlinear) plane frame analysis based on the Direct Analysis Method in AISC (reduced stiffness, notional loads, etc.) to use for designing Moment Frames. I already programmed a first order plane frame analysis program in C++ that works perfectly. My question is when doing a second order analysis, how should I apply the loads. I could apply the loads all at once and do Newton-Raphson iterations until I converge on a solution for the displacements, OR I could apply the gravity loads all at once and the lateral loads incrementally like a pushover analysis does, OR I could apply all of the loads incrementally. Computational time is only a little bit of an issue because the moment frames we work with are pretty small BUT I do run 14 or so load combinations and I check several different designs (meaning different W-Shapes). That means if I am checking 20 designs that would be 20 x 14 = 280 analyses and that usually takes my program about 25 seconds or so. Any input would be great because I really am just sort of flying by the seat of my pants on this project and I couldn't find any information that I thought was relevant to my specific project.

RE: Nonlinear Plane Frame Analysis

For second order analysis I would think applying all the gravity loads first and then increment your lateral loads would be the most appropriate. This would result in the limiting p-delta effect, as opposed to incrementing all the loads at once which could result in a higher permissible lateral load at failure.

RE: Nonlinear Plane Frame Analysis

It would be better to move the discussion to the other thread, since there are six replies there.

Doug Jenkins
Interactive Design Services

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