While conventional compression members including W-shapes are typically limited by flexural (Euler) buckling about the local weak axis
of bending, cruciform members in combined compression and bending are typically limited by torsional buckling.
These comparisons reveal that the presence of residual stresses play an important role on both carrying capacity and inelastic behaviour, during the loading process, and this effect becomes more effective with highest compressive axial load and when bending takes place about weak axis bending.
As it can be seen, the strain softening effect exhibited by the concrete in compression ([gamma] > 0) indicates lower bending capacity of cross section and also "snap-back" behaviour for bending-moment-curvature about weak axis; this effect is more accentuated as degree in confinement is decreased.
The complete moment-curvatures have been depicted both for strong and weak axis of bending and the plastic status of the cross-section associated to different values of the reference strain imposed in the most compressed point of the cross section has been revealed on the graph.
The numerical studies carried out in the present study reveals that the presence of the residual stresses, for encased steel section, play an important role on both ultimate strength capacity and inelastic behaviour, at different stages of loading, and this effect becomes more effective with highest compressive axial load especially when bending takes place about weak axis of the steel profile.
where [E'.sub.T] = enhanced fictitious E of the truss web with T-brace; [E.sub.W] measured E of the test web; [I.sub.W] = measured I (weak axis) of the test web; [E.sub.B] = measured E of the brace; [I.sub.B] = measured I (strong axis) of the brace.
Since we desire a fictitious E for the web that is buckling about the weak axis, the effective [E'.sub.T] is obtained by dividing the fitted regression equation by the weak axis I of a 2 by 4 web (0.984 [in..sup.4]) as follows: