Z Rinaldi

Static vs. Modal Analysis of Asymmetric Buildings: Effectiveness of Dynamic Eccentricity Formulations

The use of modal analysis appears necessary in order to reduce both displacement demand under weak seismic events and ductility demand under strong earthquakes. Static analysis can be effective only if used with proper values of additional eccentricities. To overcome the inaccuracy of the code formulations, the authors propose a simple procedure that gives the exact values of these eccentricities and discuss the influence of the main parameters that govern the structural behavior. They also point out the difficulty in evaluating some parameters (stiffness radius of gyration, structural eccentricity) in the case of multistory buildings and discuss the validity of simplified formulations proposed to overcome this problem. The effectiveness of static analysis, applied to three-dimensional multistory structures with properly evaluated corrective eccentricities, is analyzed with reference both to regularly asymmetric multistory schemes and to an actual irregularly asymmetric structure (the main building of the Faculty of Engineering at the University of Catania, Italy).

A simplified methodology for the evaluation of the residual life of corroded elements

Steel corrosion is one of the most common causes of deterioration of reinforced concrete structures. In fact, the chemical attack causes cracking in the concrete and a number of related effects that weaken the capacity of the composite, as well as reducing the cross-section of the rebars. It is therefore extremely valuable to have methods targeted to the evaluation of the structural damage induced by corrosion for estimating the residual load bearing capacity of a structure, and then for planning the maintenance interventions. The aim of this paper is the development of a simplified methodology capable of providing conservative estimates of the residual life of corroded structures. Because of the great amount of results obtained by the authors, general relationships between the corrosion level and the residual strength and ductility of beams are derived, and their evolution is predicted using conventional deterioration models. The methodology proposed is validated using experimental results from literature.

Precast concrete tunnel segments with GFRP reinforcement

AbstractThe possibility of substituting traditional steel reinforcement with glass fiber–reinforced polymer (GFRP) bars in precast concrete tunnel segmental linings is investigated. The use of GFRP...

Statistical analysis of seismic behaviour of steel frames: Influence of overstrength

Abstract The influence of structural overstrength on the seismic behaviour of steel structures and on the assessment of the q factor has been studied by means of a suitable procedure, based on the selection of a significant set of homogeneous historical earthquakes and on the statistical analysis of the dynamic inelastic response of the structure to these accelerograms. Six schemes of steel frames, proportioned according to different design criteria and therefore with different amounts and distribution of overstrength, have been analysed. Three values of the behaviour factor have been considered for each one. The large number of results, obtained by more than 4800 dynamic analyses, has been elaborated in a statistical way, providing damage level indexes which express the probability of yielding and collapse and the plastic level reached, both for the single section and the whole frame. Interesting conclusions have been obtained. In particular, the effectiveness of the capacity design criteria in reducing the probability of collapse of frames has been highlighted. Similar good results have been obtained even when the same overstrength is given to all columns, without any particular attention to its distribution, while the increment of the beam resistance was not favourable in any case. Moreover, a very large improvement in safety has been obtained with just a little increase in the column strength over that supplied by the application of the capacity design criterion. The global behaviour appears thus connected to a new parameter, herein defined and named “effective behaviour factor”, which takes into account the mean overstrength both of beams and columns

Influence of the steel properties on the ductility of r.c. structures

Aim of this paper is the evaluation of the steel properties influence on the behaviour of reinforced concrete structures, with particular reference to the ductility characteristics. A simplified beam model, subjected to bending moment and axial force, is developed and the relation between average strength and mean deformation is obtained. Furthermore the phenomenon of strain localization in the steel is pointed out.

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...

Numerical modelling of corroded RC columns repaired with high performance fiber reinforced concrete jacket

Reinforcement corrosion can lead to a severe damage in reinforced concrete columns with subsequent loss of bearing capacity. This condition can be deleterious in case of a seismic event. The possibility of repairing and strengthening damaged columns with high performance fiber reinforced concrete (HPFRC) jacketing has been experimentally investigated by some of the authors in previous papers, through full-scale tests on specimens under cyclic loads. The main aim of the intervention was not only to restore the original bearing capacity but also to increase the column durability. In the present paper, a numerical model is developed with the FEM software Diana in order to simulate the cyclic behaviour of corroded r.c. columns reinforced with HPFRC. Particular attention is devoted to the simulation of the corrosion phenomenon and to the strain localization due to the jacket presence. The chemical attack is defined in such a way to account for both the geometrical and mechanical variations of the bar properties. The numerical analyses represent a very useful tool for highlighting the main parameters that have to be considered in evaluating the behaviour of the damaged and then repaired elements. Finally, they constitute a support for the design and, as a consequence, for the reinforcement optimization.

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.

Redistribution of Bending Moment in Continuous Reinforced Concrete Beams Strengthened with Fiber-Reinforced Polymer

The main aim of the paper is the analysis of the moment redistribution capacity of continuous reinforced concrete beams strengthened with fiber-reinforced polymer (FRP) sheets. The interest of the topic lies in the well-known aspect related to the reduction of ductility, very often exhibited by FRP-strengthened structures. This lack of ductility can strongly affect or even prevent the redistribution of bending moments in continuous FRP-strengthened structures. To study this problem, an analytical model, developed by the authors, is adopted, which is able to simulate the nonlinear behavior of reinforced concrete beams with external reinforcement. The obtained results are validated with numerical outcomes and experimental data available in the literature. A wide parametric survey allows the authors to point out the influence of the amount of FRP and its arrangement on the bending moment redistribution capacity of different continuous beams. Finally, a simplified formulation for the evaluation of the redistribution ratio is proposed and its effectiveness is highlighted.

Ultimate Behaviour Of R.c. Frames Under Seismic Loads: Influence Of Design Parameters

A procedure for the analysis of the ultimate behaviour of reinforced concrete (R.C.) frames under seismic loads is defined in detail and it is applied to four schemes, each one designed many times with different behaviour factors and design criteria. The results obtained confirm the effectiveness of the adopted procedure, pointing out the influence of the intensity of the seismic event on the structure. The possibility of relating the entity of damage and the probability of failure to the design parameters allows a proper evaluation of the influence of these parameters, giving the national authorities a powerful tool particularly useful in order to define the optimal value of the boxed coefficients to be inserted in Eurocode 8.