Papers by Author: Giuseppe Mancini

Abstract: According to Eurocode, robustness is the ability of a structure to withstand events like fire, explosions, impact or the consequences of human error, without being damaged to an extent disproportionate to the original cause.Avoiding the progressive collapse of a building in presence of accidental loading conditions is one of the challenges for the designers.The tie-force method is actually one of the most used design techniques for resisting progressive collapse, whereby a statically indeterminate structure is designed with reference to local simplified models determined in accordance to the failure mode considered.In this work a computational study of a reinforced concrete frame is presented. The beam-column assembly represents a portion of the structural framing system of a ten-story reinforced concrete frame building and is subjected to monotonically increasing vertical displacement of the center column to simulate a column removal scenario.Two different finite element models, with distinct levels of modeling, are used in order to compare the numerical results with the experimental ones coming from a full-scale test, and evaluate the ability of the models to simulate the structural behavior of the frame.

Abstract: Bond between steel and concrete plays an important role in the structural behaviour of reinforced concrete structures. In the present paper, bond tests on r.c. specimens in presence of corrosion are performed in order to evaluate the effect of corrosion on bond mechanism. The results of the tests on concrete specimens with RILEM type shape, reinforced with ribbed steel bars of 12 and 16 mm of diameter, with and without confinement, in presence of an increasing level of corrosion up to 20%, are presented. An electrochemical procedure using a current density of 200 µA/cm² is employed to produce corrosion. The test results show the effect of oxidation of the reinforcement at the interface with concrete and consequent surface cracking, the change of performance in terms of bond and the change of failure mechanism.

Abstract: The design of concrete structures exposed to environmental attack requires serious attention for concrete durability. Early age cracking due to autogenous deformations should be avoided.In this work the study of the structural effects of hydration heat and rheological behaviour of a massive concrete casting is presented. The object of the study is a skyscraper foundation slab. Aim of the work is the numerical simulation of what occurs to the structure during the hardening, in order to avoid unforeseen autogenous cracking and therefore the choice of a tailor-made concrete mixture able to fulfil the performance criteria.Non-linear finite element coupled thermal and mechanical analyses have been performed taking into account: hydration heat generation and dispersion, dimension and sequence of the casting, evolution of concrete mechanical properties in time during the hardening reaction, creep and differential shrinkage.

Abstract: The paper addresses a generalized perturbation method for the uncertainty analysis of concrete structures subject to reinforcement corrosion. The initiation phase is modelled by the well known Ficks 2^nd law of diffusion. Deterioration models derived from experimental studies and a non-linear finite element (FE) model are used to simulate the structural behaviour of beams from the serviceability to the ultimate conditions. The time of corrosion initiation and the failure load are expressed by a Taylor series expansion about the origin of the space of independent standard normal random variables.

Abstract: In the present work, an experimental campaign on reinforced concrete elements subjected to simultaneous loading and degradation due to corrosion is presented. The specimens are loaded in tension and the cycling action is designed in order to simulate in terms of stress peak and stress variation, the effect of the passage of vehicles under fatigue design situations. The environmental action is simulated by means of corrosion induced with an electrochemical process; the corrosion rate is chosen in order to obtain about 27 years of equivalent carbonation attack within 25 days of test. In the mean time, 6.5·106 loading cycles are achieved. In addition to those standard tests, also other static tests were conducted in order to have a comprehensive analysis of the deterioration processes. Evolution of transversal crack due to loading and of longitudinal cracks due to corrosion is monitored. They can be related to the internal bond condition between steel and concrete. Results highlight the differences in terms of corroded and uncorroded specimens, static and cycling test and also different loading amplitude. Finally it can be observed as the growing of the damage is significantly different when a cycling action, combined with a chemical attack, is present.

Abstract: Bond between steel and concrete in reinforced concrete structures plays a fundamental role. The stress transfer mechanism depends on the condition of the contact surface between the two materials, the mechanical characteristics of concrete near the rebar and on the available level of confinement. Corrosion of reinforcing bars in concrete structures modifies those three factors. Because of corrosion, on the rebar surface a granular oxide layer is present and with its expansion it generates a significant radial pressure; consequently tensile stresses grow till cracking of the concrete cover with a subsequent reduction of the confinement effect. Moreover the presence of a mechanical action modifies the resisting mechanism producing an increasing damage. In this study, a model is presented for the numerical simulation of experimental tests on r.c. ties subjected to mechanical action; furthermore some considerations on reinforced concrete ties subjected also to corrosion effect are reported. From those analyses it is possible to estimate a modified bond-slip law between the reinforcing bars and the concrete, in order to take into account the level of damage.

Abstract: Corrosion modifies the steel-concrete interface in reinforced concrete structures. The efficiency of the connection between the two materials is reduced and the structural behavior both in service and in ultimate condition is affected. Moreover in structures subjected to cyclic load, a simultaneous mechanical deterioration due to the load is present. In this work an experimental analysis on reinforced concrete structures under both cyclic load and corrosion of reinforcing bars is presented. Three couples of reinforced concrete ties are connected in series and subjected to the same stress variation in order to produce the cracking conditions and to activate the bond mechanism. However, while one of the two reinforced concrete ties is only subjected to cyclic load, the second one is also corroded using an accelerated electrochemical corrosion process. The simultaneous effect of the cyclic load and corrosion is evaluated monitoring the crack opening on the structures during the test and by means of visual inspection of the sample. The test results show the correlation between the mechanism of bond and the average level of stresses for an amplified stress range.