Sulla verifica di colonne snelle in c.a. alla luce delle recenti disposizioni normative

Stability-related issues, usually controlling design of steel structures, are getting more and more important even for concrete ones as more and more resistant materials are nowadays available and allowed by codes of standard for structural concrete. Indeed, increasing concrete strength results in reducing cross sections and, consequently, increasing member slenderness directly affecting second-order effect sensitivity of structures. Structural codes currently provide designers with several proposals for slenderness limits of concrete members. Those limits are usually derived on the basic assumption that second order effects are not greater than 10% of the first order ones. Consequently, simple theoretical considerations based on the theory of elastic stability lead to define relevant slenderness limits of concrete members. Despite that theoretical simplicity, the behaviour of concrete structures is affected by non-linear phenomena such as concrete cracking and steel yielding which cannot by easily handled within the elastic theory. The present paper, starting from simple theoretical considerations aimed to recognize the basic parameters needed for defining consistent slenderness thresholds, deals with assessing various proposals derived by the scientific literature. In particular, focus is placed on two formulations recently adopted by both the European and the Italian codes for limiting slenderness of concrete members. Numerical analyses point out that those formulations are often unconservative.