S Imperatore

Strength decay of RC sections for chloride attack

Purpose – Corrosion of reinforcement, and mainly the one induced by chloride attack, is one of the leading causes of deterioration in reinforced concrete structures. Then, it is very important to develop a simplified analytical tool, able to simulate the corrosion processes and the consequences for the structural safety. The paper aims to discuss these issues. Design/methodology/approach – Aim of this paper is the definition of a simplified integrated procedure, able to predict the decay with the time of the bending moment and axial force resistance of a reinforced concrete section, exposed to a chloride attack. Starting from various literature findings, the rebar mass loss in time is evaluated and related to the chloride distribution and content in time. Then the mechanical properties of the corroded rebars are evaluated by means of strength decay laws developed by the authors. Finally, moment-curvature relationships and bending moment – axial force (M-N) interaction envelopes are defined. Findings – The...

Force reduction factor for out-of-plane simple mechanisms of masonry structures

The dynamic behaviour of existing masonry buildings mainly depends on the out-of-plane response of the vertical walls. A proper evaluation of their response can be analytically performed considering the dynamic equation of motion of the rigid body, in the framework of rigid in compression no tension material. The above equation is numerically solved with increasing magnitude of the seismic action, until the collapse condition of the wall, due to a lack of equilibrium, is reached. In the paper two local collapse mechanisms are considered, the two sided and the one sided rocking. The influence of considering a simplified trilinear moment-rotation law is also discussed. For each mechanism, the force-reduction factor, defined as the ratio between the seismic acceleration value causing the collapse of the masonry element and the one corresponding to the activation of the rocking motion, is evaluated. The dependence of this factor on the main parameters of the model is deeply investigated by means of numerical analyses, varying the geometrical characteristics of the panel, the energy dissipation model and the features of the seismic input. A power function law between an effective force reduction factor, defined as the ratio of the force reduction factor multiplied for the gravitational acceleration to the peak ground acceleration, and the Housner Spectrum Intensity is identified for both the examined models. These laws allow accounting for the so-called scale effect within a force-based framework. Eventually, novel formulations for evaluating the force reduction factor of two and one sided rocking systems are here proposed. Their effectiveness has been also highlighted considering both spectrum-compatible accelerograms and natural records.

Mechanical Behaviour of Corroded Rebars in Reinforced Concrete Elements

Corrosion of the reinforcement is a common form of degradation of reinforced concrete structures. As a matter of fact the chemical attack varies the mechanical properties of both the steel rebars and concrete, and the bond characteristics. The study presented in the paper is mainly devoted to the analysis of the corrosion effects on the steel rebars and at the steelconcrete interface, and their influence on the local and global behaviour of simple R/C elements. At this aim, experimental analyses are developed, for the calibration of the constitutive relationships of both the steel rebars and the bond-slip response, in presence of corrosion. Finally the obtained laws are implemented in an analytical model, developed by the authors, in order to evaluate the influence of the corrosion on the global behaviour of simple R/C beam elements.

Seismic Behaviour of Rocking Elements Reinforced with Composite Materials

Seismic behaviour and vulnerability of existing masonry structures are typically characterized by out-of-plane response of vertical walls. The dynamic response of such elements can be analytically assessed considering the dynamic equation of rigid bodies not resistant to tensile stresses. Many studies available in literature have highlighted the vulnerability of this type of structures against out-of-plane movements. In order to withstand horizontal seismic actions, appropriate and effective retrofitting interventions have to be properly designed. In this paper, the rocking response of a masonry wall retrofitted with elastic GFRP bars is investigated. A parametric survey is also carried out, to evaluate the increase in strength of the masonry wall, due to the presence of the composite material.