STABILITY CHECKS IN SLENDER R/C COLUMNS ACCORDING TO RECENT CODE TRENDS

Stability-related issues are becoming increasingly important in concrete structures, because of the availability of better and better concretes, that are nowadays accepted by the codes of practice for the design of R/C and P/C structures. Increasing concrete strength results in reducing cross sections and enhancing member slenderness, with a direct influence on structural sensitivity to second-order effects. Structural codes currently provide designers with various proposals for the slenderness limits of concrete members. These limits are usually based on the assumption that second-order effects do not exceed 10% of the first-order ones. Consequently, simple theoretical considerations, based on the theory of elastic stability, allow defining the slenderness limits for concrete members. However, such nonlinear phenomena as concrete cracking and steel yielding make any simple approach in handling stability problems highly questionable. In this paper, starting from rather simple theoretical considerations aimed at identifying the basic parameters necessary for defining consistent slenderness thresholds, various proposals available in the scientific literature are presented and discussed. Specific attention is devoted to two formulations recently adopted by both the European and the Italian design codes, for limiting the slenderness of concrete members. Numerical analyses, however, show that these formulations are often non-conservative.