A method is proposed for the analysis of the nonlinear behavior up to failure of reinforced-concrete membrane elements. The approach considers a linear elastic behavior for concrete before cracking; ...after cracking, the cracks are assumed as having a fixed direction and uniform spacing and cracked reinforced concrete is modeled as an orthotropic material. The basic element of cracked reinforced-concrete membrane is defined and the related stiffness matrix is proposed. The quantities that govern the problem are the opening and the sliding of the crack lips, as well as the strain of the concrete struts that are located between cracks. Applied to a local analysis of cracked reinforced concrete, the above variables allow for the effective modeling of compatibility and equilibrium conditions and take into account phenomena such as aggregate interlock, tension stiffening, and dowel action. To verify the reliability and capability of the proposed method, some comparisons with experimental observations of relevant tests are made.
A mechanical model is proposed to study the behaviour and ductility of reinforced concrete (RC) beams. The aim is to reproduce numerically the experimental results of Weiss et al. (2001), where a ...size effect on the average strain of compressed concrete has been measured by changing the distance of external loads in four point bending beams. Precisely, the mechanical responses of RC members in bending are evaluated by modelling the progressive crushing of compressed concrete. A good agreement between numerical and experimental results has been obtained for different types of beams. The proposed approach also shows some differences from Eurocode 2, where size effect on the structural response of compressed concrete is not taken into account.
Flexural Deformability of Reinforced Concrete Beams Fantilli, Alessandro P; Ferretti, Daniele; Iori, Ivo ...
Journal of structural engineering (New York, N.Y.),
09/1998, Letnik:
124, Številka:
9
Journal Article
Recenzirano
In reinforced concrete beams, the sectional definition of the moment-curvature relationship is not straightforward owing to the presence of cracks. In general, this problem has been solved by ...considering a representative portion of the beam and by defining the curvature 1 r as the ratio between the rotation of the portion considered and its length. Large portions of the beam with many cracks lead to "average" moment-curvature relationship, while small portions delimited by two consecutive flexural cracks lead to "local" moment-curvature relationship. The difference between these two definitions is studied in this paper introducing a "general model." With this model the entire beam is modeled through a succession of blocks divided by flexural cracks taking into account the bond between steel and concrete. Due to the practical impossibility of univocal definition of the crack pattern evolution, it is proposed to use a "range model." This "range," delimited by the curves of maximum and minimum deformability, includes the moment-curvature relationship (locals and average) obtained from all possible crack patterns.
According to many code requirements for concrete structures, the stress in the compressed part of reinforced concrete (RC) beams in bending is usually computed by means of uniaxial stress-strain ...relationships. These approaches sometimes are not able to reproduce the structural response of the beam when crushing of concrete in compression occurs. As a consequence, both the bearing capacity of RC structures and their ductility are roughly estimated. In this paper, the postpeak behavior of compressed concrete is modeled through sliding planes up to the expulsion of v-shaped block. The concrete damage on the surface of these-planes is the cause of the softening branch in the moment-curvature diagrams of RC beams. The proposed mathematical description of the sliding phenomenon also shows how it is impossible to define an univocal stress-strain relationship for concrete in compression, whose softening behavior depends both on the dimension of the compressive zone and on strain gradient (i.e., the curvature).
Failures of structures are often tragic events, however represent an opportunity to improve the understanding of phenomena. In this paper, after the review of Bridge collapses, on August 14, 2018, ...the history of Polcevera Bridge is presented, starting from aging considerations done by its designer Riccardo Morandi in 1981, analyzing the outcomes of inspections in the years from mid ‘80s with references to Italian Regulations on inspections, the interventions done during bridge life, and finally some considerations on its collapse. The case is certainly a reference for reinforced concrete bridges built just after the 2nd world war in a highly corrosion-prone environment due to nearby sea and industrial as well as chloride pollution. Large reference is done to data included into the Report of the Commission of Italian Ministry of Infrastructures for the failure of Polcevera Bridge. Monitoring for assessment of performance decay due to corrosion is discussed with reference to the meaningful example considered.
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