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Aging and corrosion of reinforced concrete structures (RCS) is becoming a global problem, thus proper procedures for simulating the structural performance of corroded RCS should be assessed. Among the main corrosion effects, concrete cover cracking and reinforcement cross-section reduction may influence the materials’ constitutive laws, moreover the confinement contribution and the lateral instability of the longitudinal rebars can be modified. In the present paper, the predictive models available in the scientific literature to assess the materials’ mechanical properties of corroded RCS are recalled and employed into a novel model to derive the theoretical moment–curvature relationships for the cross-section of square and rectangular corroded reinforced concrete elements. The model accounts for cover spalling, buckling of longitudinal reinforcing bars, reduction in confinement pressures, reduction in concrete constitutive law due to the concrete cracking induced by rust formation and decay of mechanical properties for corroded reinforcements. The obtained results are compared with the classical simplified models for corroded RCS, highlighting that buckling and confinement variations cannot be disregarded into a reliable modelling strategy, especially when local ductility plays a key role in the performed investigations.

Since the concrete cover cracking is the earliest visible manifestation of corrosion, a relationship between crack opening and corrosion level can be a useful non-destructive tool to estimate the degradation level of an existing RC member. In the present paper, the predictive formulations available in the scientific literature estimating the crack width due to a given corrosion level are accurately described and their reliability is evaluated by a statistical analysis of the error in the predictions. At this aim, an extensive dataset on crack openings of artificially corroded RC specimen reinforced with a single bar, or more bars with large spacing, has been collected. Finally, a novel relationship for the assessment of the corrosion degradation from the surface cracking is presented and validated.

Background: Corrosion of the reinforcing steel is a significant issue in construction engineering. As the corrosive attack propagates, the oxides accumulated on the steel-concrete interface cause a radial internal pressure in the structural element and induce a tensile stress state in the concrete with the consequent cracking. Except for few cases, the main outcomes on the behavior of reinforced concrete structures damaged by corrosion come from experimental results on artificially corroded specimens. For many years, the scientific community has been discussing the feasibility of artificial techniques to simulate the corrosion process in structural element. Specifically, the most disputed method is the accelerated electrolytic corrosion test, often characterized by high current intensities in order to reduce the duration of the experimental surveys. Objective: In the paper the influence of the current density on the degradation of a reinforced concrete element is investigated with particular reference to the kind of formed oxides and to the crack width. Methods: An experimental survey on steel rebars embedded in concrete cylinders and subjected to an electrolytic corrosion has been performed, with different increasing current densities. Furthermore, an analytical model, based on the classical thick-walled cylinder theory already proposed by the authors, is applied for validating the experimental results. Results: The oxides produced by artificial corrosion with different current densities are analyzed with X-ray diffractometry measurements. The influence of the current density on the crack widths is also pointed out. Conclusion: The analyses of the obtained results show that for the analysed specimens and current density range, no significant differences are found for the oxides composition. On the contrary the influence of the current density on the crack width is pointed out, and an upper limit of this parameter is indicated.

The seismic performance of masonry churches is mainly governed by the out-of-plane mechanisms. Among them, the greater seismic vulnerability can be associated to the out-of-plane mechanism of the façade. If the masonry quality ensures a monolithic out-of-plane behaviour, the dynamic analysis of a rigid rocking block allows a reliable estimation of the seismic capacity of the façade, provided that the element boundary conditions are well assessed. In the present paper, the literature rocking models are adopted for a vulnerability assessment of churches' masonry façades characterized by different geometries. At this aim, fragility curves are defined by means of the Cloud Analysis approach considering earthquakes recorded in the Central Italy area to account for the record-to-record variability.

In the present work the mechanical behavior of reinforcing steel rebars deteriorated by corrosion is investigated. The effects of both the degradation morphologies (uniform and localized) are considered. In particular, an experimental survey on artificially deteriorated steel rebars, with different diameters and subjected to different corrosion degrees, was carried out in the Laboratory of the University of Rome Tor Vergata, in order to obtain a uniform corrosion. The specimens were subsequently subjected to monotonic tensile tests in order to investigate the influence of the uniform corrosion on their constitutive relationships. On the basis of the obtained responses, decay equations for the main mechanical properties are developed. Finally, with reference to the pitting corrosion, the data presented in literature are collected and statistically analyzed for defining, in this case also, degradation equations suitable to estimate the variation of the steel mechanical properties.

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.

The historical masonry buildings are characterised by a great vulnerability regard the seismic action, as the recent events occurred in Central Italy have highlighted. During the seismic emergency the authors, in collaboration with the Civil Protection Department as part of the ReLUIS activities, have carried out usability inspections, analysing also the case study described in this paper. The structure, a school in Teramo, was already affected by previously seismic damages and it has been highly involved by the seismic events abovementioned. In this work the results of first inspection, reported in the AeDES form, and a more accurate visual inspection are presented in terms of detection of the crack patterns and evaluation of the seismic damages index. Moreover the vulnerability index has been calculated according to the GNDT 2° level method. The vulnerability index is finally used to calculate the damage index expected for the seismic intensity registered during the seismic event of October 30, 2016, and compared with the observed post-seismic damage level.

The out-of-plane behaviour of the walls as a consequence of an earthquake is the main vulnerability of existing masonry structures. In the case of rigid in compression not tensile resistant material, incremental dynamic analyses may be employed to evaluate the effective strength of a rocking element. When the seismic capacity of the wall is inadequate, retrofit interventions are required to assure an acceptable safety level. Conventional seismic retrofitting techniques on masonry walls influence the seismic performance of the element, which typically is modified in an out-of-plane bending behaviour. In this paper, analytical investigations are presented to investigate the possibility of a seismic retrofitting intervention able to increase the seismic strength of the wall without modifying its seismic behaviour. The analysed retrofitting technique consists in the application of composite vertical bars either in the middle section of the wall or at its external surfaces. The seismic behaviour of the retrofitted masonry wall is analytically evaluated by means of a parametric incremental dynamic analysis, carried out with an ad hoc in-house software. The effectiveness of the intervention is analysed in terms of level of seismic improvement, defined as the ratio between the seismic capacity of the reinforced and unreinforced walls.

The researches on the bond behavior of corroded reinforcements are finalized to the assessment of the structural serviceability loss, providing appropriate tools for the evaluation of the structural integrity, i.e. relation between the corrosion rate and the cracks width detected during visual inspection on existing structures. Unfortunately, several contradictions can be found in the literature and a comprehensive interpretation of the influence of both the concrete cover depths and the reinforcement typology on the corrosion process is still missing. The present work describes the research activities planned in the convention "Effect of corrosion on the steel-to-concrete interaction" and finalized to understand the bond-slip decay in presence of corrosion. REFERENCES The paper is part of the research, “Effect of corrosion on the steel-to-concrete interaction” between Niccolò Cusano University and Oslo Metropolitan University, that financially support the project.

Reinforced Concrete (RC) structures frequently are deteriorated by corrosion attack where pitting morphology is the worst form of degradation. Appropriate vulnerability analyses, accounting for the variation of mechanical properties of material during the time, give an assessment of the residual service life of corroded structures. Aim of the present paper is to evaluate any variation in the seismic behaviour of an irregular poor-designed RC frame subjected to the chloride attack. The progressive stiffness degradation and the effects of higher modes are considered in the study by means of displacement-based adaptive pushover analyses.

Worldwide, steel corrosion is one of the greatest deterioration problems for reinforced concrete structures. Comparing some experimental results from literature with a complex FEM model, the present paper points out the principal aspects that characterize the static behavior of reinforced concrete (RC) elements damaged by corrosion. Moreover, the nondimensional abaci defined for some specific case studies finalized to the evaluation of the residual flexural strength of corroded elements highlight the dangerousness of the corrosion degradation if the failure of the element is governed by the steel. This research received no external funding.

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.

Corrosion is the most commonly severe defect in reinforced concrete (RC) structures and it mainly causes reduced rebar cross-section. The corrosion rate is the determining parameter of the progress of corrosion-induced damage. The present work is focused on the application of finite element (FE) analysis, using DIANA, to predict the residual capacity of reinforced concrete beam with different degree of corrosion. To this aim, existing experimental data is used to develop a FE model of corroded beams and to investigate their behaviour. This model is validated to predict the impact of time and current rate of corrosion on the residual load carrying capacity of corroded RC beams. Open Access CC-BY. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

The aim of this work is to evaluate the influence of corrosion on the lateral displacement capacity and on the global ductility of reinforced concrete (RC) elements, using finite element (FE) analysis. The corrosive phenomenon is simulated accounting for its consequences on the reinforcing bars (variation of the steel geometry and mechanical properties), on the concrete (cracking) and at the interface (variation of the bond-slip behaviour). The parametric analysis, using numerical models, highlights how corrosion significantly changes the structural performance of the element in terms of deformability.

Existing reinforced concrete elements are typically subjected to ageing and corrosion, leading to significant structural capacity decay. The variation in the steel-to-concrete interaction is one the first effects of corrosion, that consequently modify the bond-slip relationship. On a structural point of view, this implies a variation of the crack pattern, an increase of the element deformability, and an enlargement of the crack width. Several studies, available in the technical literature, analyse the corrosion influence on the bond properties by means of small specimens, in which only the local bond-slip behaviour can develop. In this paper, in order to investigate the problem at a full-scale level, three meters long tie rods were cast, artificially corroded and tested in the Laboratory of Materials and Structures of the University of Rome Tor Vergata. Each specimen was characterized by a 150 × 150 mm2 cross-section and reinforced with a O16 steel bar placed at the centerline of the element. The specimens were artificially corroded up to about 4% corrosion level (in terms of mass loss) and subjected to tensile test. The obtained results clearly highlight the influence of the corrosion of the bond transmission mechanism.

The problem of the durability of reinforced concrete structures is arisen, dramatically, in the last decades, showing that one of the most dangerous degradation phenomena is connected to the rebars corrosion. When active corrosion grows the oxides occupy a volume of about 2–4 times, with respect to the sound bar, causing a loss of bond, cracking and cover spalling. In this paper the corrosion effects at the steel–concrete interface are analysed. At this aim, pull-out tests are carried out, with different corrosion levels, for the definition of the bond-slip constitutive relationships of the damaged rebars. Furthermore, an analytical model is developed for evaluating the internal pressure due to corrosion products, for concrete specimens without stirrups, in order to provide a procedure for the definition of the maximum bond as a function of the corrosion percentage. Finally the analytical results are validated through a comparison with the experimental outcomes.

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. 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 strength variation with the time can be easily evaluated and then the life cycle and the timing of repair or rehabilitation strategies can be estimated. Originality/value The proposed methodology can be considered a very simple, but useful tool for a first analysis of the strength reduction in time, due to chloride pitting corrosion, before performing more complex and time-spending analyses.

In moderate and aggressive environmental condition, old reinforced concrete structures are often subjected to corrosive phenomena. Corrosion causes cracking, loss of diameter in reinforcement and variation of the bond behavior between steel and concrete. Then, in presence of cyclic actions like the seismic ones, old R.C. elements vary their ultimate drift, ductility, plastic rotation capacity and energy dissipation with the corrosion level. The problem is of current interest: the issue has been introduced in some paragraph of the Model Code 2010 and a committee is now drafting a new document on assessment strategies on existing concrete structures also damaged by corrosion.In this work, a first step on the analysis of the impact of the corrosion on the seismic behavior of R.C. elements is assessed: by mean FEM analyses, of a poor detailed column/foundation joint is analyzed in a parametric way in order to evaluate the influence of the bond-slip degradation by corrosion on the element flexural capacity.

The ultimate behavior of thin reinforced concrete structures, such as slabs, can be governed by punching due to point loads. This premature brittle failure mode can occur in bridge deck slabs, often subjected to severe conditions of loads concentrated in small areas, and characterized by a reduced thickness. In this kind of structures, a proper punching reinforcement is not applicable, but the local and global behavior can be improved by the addition of short fibers. Three full-scale slabs, simulating bridge decks, were tested in the Laboratory of the University of Rome Tor Vergata, to investigate the effect of lightweight fiber reinforced material on the punching shear resistance. Furthermore, ashes coming from the combustion of Municipal Solid Waste (MSW), with pozzolanic reaction, were added to the concrete mix. The obtained results are presented, discussed and compared with the MC2010 provisions.

This paper presents the experimental behaviour of two reinforced concrete T-beams strengthened in shear with CFRP. The beams are extracted from an important building of the mid-'30s in Rome. The goal of this research is to evaluate the shear strength of the retrofitted beams with the simultaneous occurrence of a negative bending moment. The tests are performed at the Experimental Laboratory of the Structural Department of the University “Roma Tre”. In the meantime the two beams are modelled with the software ATENA in order to perform numerical simulations of the tests. The numerical results seem to be in good agreement with the experimental data in terms of load– displacement response, strain state, crack pattern and failure mode.

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.

This paper presents a finite element analysis on two reinforced concrete beams, extracted from an important building of the '30s in Rome, strengthened in shear with C-FRP and subjected to the simultaneous occurrence of a negative bending moment and shear stresses. The commercial program ATENA was used to perform numerical simulations of the tests. The numerical results seem to be in good agreement with the experimental data in terms of load-displacement response, strain state, crack pattern and failure mode.