PDELTA QUESTION CLARIFIED

Question

PDELTA QUESTION CLARIFIED

IJR (Structural)

(OP)

26 Dec 00 03:13

Thanks CV and NO KNOW for response. Let me clarify. Guide to Stability Design Criteria for Metal Structures suggests Pdelta as one among three procedures for determination of strength of frames designed using Allowable Stress Method(item 15.12,1976),suggesting K=1 and direct use of second order moments. Edward L. Wilson in his book "3D static and dynamic analysis of Str." page 11-11 also refers to this procedure. In K methods, compressive strength is divided by a factor of safety dependent on K-based slenderness. In moment magnification actual compressive stress is divided by "allowable" Euler stress which is also K-based.

My question is we have two points here: Allowable Compressive Strength and Moment Magnification due to axial load level. Will blindly putting K=1 work or are there extra considerations?.

Merry X-mas to all fellow engineers

cv (Structural) · Answer 1 · 2000-12-27 05:54:48

I think Compressive Strength is itself and Moment magnification comes from the displacment of nodes and bow efect between nodes. If the FEA have both PDelta ( displacment of nodes ) and Pdelta ( bow efect ) then we are near the real behaviour of the model. I think the only thing and the most important is to load the model by steps of load and not suddenly, to give way to the update of the geometric matrix.

I do appreciate your coments.
Regards

CV
carlosvalinhas@netcabo.pt

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PDELTA QUESTION CLARIFIED