L’influenza dei materiali sulla deformabilità degli elementi in c.a.

The assessment of seismic demand of reinforced concrete structures, both in terms of forces and displacements, through linear or nonlinear analysis methods, is necessarily based on a correct evaluation of the deformability at yielding of each structural element. This work presents and discusses the results of an extensive parametric analysis aimed at the evaluation of the influence of the mechanical characteristics of materials (steel and concrete) on the deformability of r.c. elements at yielding, both at the section and at the element level. The study is particularly aimed at the characterization of the deformability of elements reinforced with plain bars and therefore representative of pre-1970’s existing buildings. Regression analyses carried out on numerical data allow the proposal of simplified expressions for the estimation of curvature, secant sectional stiffness and fixed-end rotation (chord rotation due to the slippage of reinforcement bars from the connection element) at yielding. The estimation capabilities of the proposed formulations is verified through a numerical-experimental comparison with data from monotonic and cyclic tests conducted on r.c. elements with plain bars.