15 Dec

Rational Buckling Analyses to AS4100 or NZS3404 (Part 4)

In the last post we looked at the basic method of undertaking a flexural buckling analysis using Mastan2 and interpretation of the results. We compared a couple of the built-in equations in AS4100 & NZS3404 relating to the \alpha_m factor and got reasonable agreement.

I stressed that getting the elastic buckling moment out of a buckling analysis does not equate to determining the design capacity. We briefly mentioned the \alpha_s factor in passing. This is a scaling factor which is determined from the reference buckling moment M_{oa} and the nominal section capacity of the member in bending M_{sx}, it is intended to essentially account for a number of 2nd order effects. Basically converting our theoretical buckling value to a “design” value that accounts for real-world things like the fact that all members have initial imperfections (they are not perfectly straight), all beams have some degree of residual stresses (which results in some regions of the section yielding prior to others and resulting in reductions in stiffness with respect to the resistance to buckling).

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