1,721,037 research outputs found
Research developments on bond between corroded steel and concrete (Key-note lecture)
No full textCorrosion of steel in concrete has the most detrimental effect on reinforced concrete structures. Among the other effects, corrosion deteriorates the interface between steel and concrete. Bond between steel and concrete is at the base of all the resisting structural mechanisms in reinforced concrete structures and therefore its modification is fundamental in case of anchorages and laps of reinforcing bars on existing structures. Despite the considerable number of research papers, some critical aspects should be taken into account when considering experimental test on bond in presence of corrosion. An overview of the latest experimental activities is presented, and some research challenges related to the reliability of test conditions and the significance of the obtained data are discussed
Residual crack width in RC and R/FRC ties subjected to repeated loads
No full textDurability of reinforced concrete (RC) structure is mostly related to the ability of concrete cover to protect the embedded rebar from corrosion initiation and propagation. As cracks due to loads or rheological phenomena are almost inevitable, the geometry of crack pattern in service is a key parameter that needs to be evaluated in plain and fiber-reinforced R/FRC members. In fact, not only the direct ingress of aggressive agents, such as oxygen and water, is a function of crack width, but also concrete carbonation and the chloride ion ingress are accelerated by the presence of wide cracks. Furthermore, the use of fiber reinforced concrete requires detailed investigations, in order to define the relationship between durability and crack width even in presence of cyclic loads. Accordingly, in this research project, crack width is measured by using traditional mechanical strain gauges and a new device based on the optical conoscopic holography. The latter allows the non-contact measure of crack profile, at the end of each loading cycle, both in plain and fiber-reinforced ties subjected to sets of repeated loads. As a result, contrarily to crack width at the peak of load, the width of residual cracks is not always reduced by the presence of fiber, and this could affect the durability of RC and R/FRC structures
Serviceability behaviour of PC structures by probabilistic and fuzzy probabilistic approaches
No full textThe evaluation of the safety level in concrete structures should be carried out considering the stochastic behaviour of the main parameters involved, not only under ultimate conditions, but also under serviceability and durability conditions. Particularly in concrete structures, the large variability of mechanical and rheological parameters may give rise to important deviations from the expected behaviour if a deterministic approach is used. On the other hand, it is well known that the probability density function and its parameters cannot be univocally defined. To overcome this problem, the fuzzy probabilistic theory may be used in the processing of stochastic parameters, taking into account their fuzzy nature. In this paper, a probabilistic analysis and a fuzzy probabilistic analysis of a bridge prestressed beam is performed in order to evaluate its behaviour under serviceability conditions, with particular attention to the crack formation limit state. Shrinkage, creep and tensile strength are considered to be stochastic variables, whilst for the other variables involved (e.g. live loads, etc.) are considered to be deterministic values. The comparison between the two approaches put demonstrates the peculiarity of the fuzzy probabilistic procedure that reproduces a more comprehensive safety estimate method
Crack opening evolution in corroded confined reinforced concrete ties
No full textCorrosion of reinforcement deteriorates reinforced concrete structures reducing the structural performance both in service and ultimate conditions. Dealing with service condition, a key aspect is the crack opening value due to load that is direct consequence of bond between steel and concrete. The addition of corrosion modifies further this relationship inducing over-proportional effects in terms of damage. In this paper the results of an experimental campaign on confined reinforced concrete specimen are presented. The study of the effect of crack opening evolution on structures subjected to cyclic loading and corrosion allows to find some relationship and to highlight the interrelation among number of loading cycles, corrosion, crack opening, tension stiffening and loss of bond
Early age behaviour of massive concrete piers
No full textIn the proposed work the study of the structural effects of hydration heat and differential shrinkage on structures realized by means of massive concrete castings is presented. The object of the study are several circular piers of a viaduct built in Northern Italy. In the first weeks after the removal of the scaffoldings an evident crack pattern was noticed on the body of a great number of piers. The crack opening was of a few tenth of millimeters. The formation of the cracks also occurred before the dead load of the girder and the service loads were applied. Aim of this work is the numerical simulation of what occurred to the structure in the first hours after the casting and in the following days, in order to establish the causes of the unforeseen cracking. A diffused cracking phenomenon rising in the first days after the casting with a pattern similar to the one seen in situ has been numerically reproduced by means of a non linear finite element coupled thermal and mechanical analysis. Crack width was then calculated according to Model Code 90 and Eurocode 2 formulations, obtaining results in good agreement with the values measured in site. The result obtained gives a clear answer of what were the main causes of the damage: hydration heat, absence of curing, dimension of the casting, differential shrinkage, evolution of concrete mechanical properties in time during the hardening reaction
Integration of Digital Image Correlation in Flexural Tests for the Corrosion Evaluation of Ferrocement Plates
No full textFerrocement is a thin reinforced cementitious composites of hydraulic
cement mortar with layers of wire steel mesh, which has been widely used in the
roofing systems in major 20th-century architectures. However, few studies have
analyzed its durability for preservation purposes and stiffens time-dependency
evolution. In the present paper the results of a recent testing campaign on ferrocement specimens subjected to a corrosive environment are presented. The experimental campaign in monitored by 3D-Digital Image Correlation (DIC) signal
processing. In particular, the external evidence obtained by the reconstruction of
the strain field may be directly correlated with the 3-D localization of the microraking formation in the tested specimen obtained by AE detection. The aim was
to assess the behavior of historical ferrocement (used by Pier Luigi Nervi in his
constructions) and its durability for identifying the best procedures to protect and
preserve it
A Model for the Analysis at ULS of Corroded RC Beams
No full textThe proposed model is able to consider the interaction between bending, shear and normal forces. Some experimental tests present in the literature, where the structural behaviour of reinforced concrete beams in presence of corrosion of longitudinal and transversal rebar was investigated, were used in the present study in order to validate the proposed model. The numerical results seem to be in good agreement with the experimental ones
Shape sensing with inverse Finite Element Method for slender structures
No full textThe methodology known as "shape sensing" allows the reconstruction of the displacement field of a structure starting from strain measurements, with considerable implications for structural monitoring, as well as for the control and implementation of smart structures. An approach to shape sensing is based on the inverse Finite Element Method (iFEM) that uses a variational principle enforcing a least-squares compatibility between measured and analytical strain measures. The structural response is reconstructed without the knowledge of the mechanical properties and load conditions but based only on the relationship between displacements and strains. In order to efficiently apply iFEM to the most common structural typologies of civil engineering, its formulation according to the kinematical assumptions of the Bernoulli-Euler theory is presented. Two beam inverse finite elements are formulated for different loading conditions. Depending on the type of element, the relationship between the minimum number of required measurement stations and the interpolation order is defined. Several examples representing common applications of civil engineering and involving beams and frames are presented. To simulate the experimental strain data at the station points and to verify the accuracy of the displacements obtained with the iFEM shape sensing procedure, a direct FEM analysis of the considered structures is performed using the LUSAS software
The Antifragility of FRC in the Crack Pattern of Reinforced Concrete Ties
No full textTo assess the durability of Reinforced Concrete (RC) structures, a model capable of predicting the crack pattern of RC ties is herein introduced. Based on the classical tension-stiffening equations, such model provides the transfer length, which in turn depends on the bond-slip mechanism between steel and concrete. The aim is to compute the length of a tie which shows a single crack in the serviceability stage. In this particular situation, if the geometry does not change, transfer length only depends on the strength of plain or fiber-reinforced concrete (FRC). Nevertheless, the experimental investigation, performed on RC and R/FRC ties with the same geometrical and mechanical properties, reveals two different crack patterns. Specifically, RC ties show multiple cracking, whereas only one crack tends to appear in presence of FRC. This dichotomy can be ascribed to the so-called antifragility, which can be considered as the capacity of FRC to gain strength from its intrinsic disorder
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