ABSTRACT
This chapter points out that the buckling behaviour of slender columns may differ significantly when RAC is used in place of NAC, contrary to short columns (chapter 18). The main parameters responsible for the difference are discussed: smaller elastic modulus for RAC; consequently, modified stress-strain law in compression (a model valid for RAC as well as NAC is proposed, which needs only to know the strength and the modulus); creep higher for RAC. Considering the lack of tests of slender reinforced RAC columns, an analogy is done with LWC (Light Weight Concrete) and some comparative tests on slender reinforced LWC and NAC columns are presented, only under short term loading. Furthermore, some parametric calculations by means of the so-called model column method are done. They show that the decrease in buckling load of RAC slender columns with respect to NAC will remain moderate for short term loading (effect of modulus), but may be important for long term loading (cumulative effects of modulus and creep). Finally, the modifications of the EC2 calculation rules at the ULS that would be necessary for RAC are analyzed, such as the limit of slenderness below which the second order effect can be neglected.
