Effect of strain hardening on the limit slenderness for semi-compact sections

The cross-sectional classification forms a key precondition for the safe design of steel sections against local instabilities, as this determines their allowable stress utilization and deformation capacity. This paper focuses on the effect of the stress-strain relationship and of strain hardening on the limiting slenderness values that distinguish between slender or semi-compact (elastic) and compact (plastic) sections. Using test-validated numerical (GMNIA) simulations on short beams, four independent cases were investigated i) elements supported on one edge in pure compression, ii) elements supported on both edges in pure compression, iii) elements of I-sections supported on both edges in pure bending and iv) elements of hollow sections supported on both edges in pure bending. The results of the numerical simulations were analyzed. In particular, the maximum achieved moment was compared with the plastic moment resistance. Thus, a statement could be made on whether the plastic moment resistance could be reached and consequently whether the cross-section should be assigned as a semi-compact (class 3) or compact (class 2) section. From this, limit slenderness values could be determined and correlations to the hardening behavior could be found and integrated into corresponding design formulas.

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