1,721,043 research outputs found
An orthotropic damage model for the analysis of masonry structures
No full textThe paper presents a new orthotropic damage model suitable for the macroscopic modelling of masonry under in plane load. The main aim is to
obtain a simple but effective tool suitable for the numerical simulation of large masonry structures. The validity of the model is confirmed by some numerical application
NUMERICAL MODELLING OF BOND BEHAVIOUR IN RC STRUCTURES AFFECTED BY REINFORCEMENT CORROSION
No full textSteel corrosion in reinforced concrete structures leads to severe degradation processes which usually affect both the ultimate and serviceability limit state performance of the whole construction. Numerical modelling of such a behaviour requires effective non linear models able to capture all the main effects of corrosion (i.e. cracking, reduction in bond strength, reduction in steel cross-section, bond degradation, etc.). This paper discusses these topics by focusing on the effects of corrosion on bond behaviour. In particular, a coupled mechanicalenvironmental damage model is used to simulate the deterioration of concrete (i.e. cover cracking and reduction of mechanical properties), while the effects of corrosion on bond behaviour have been dealt with using two
different approaches, one based on a “frictional type” law and the other on a “damage type” law. A comparison between experimental pull-out test data and numerical results verifies that the proposed procedures can effectively simulate the effects of corrosion on bond behaviour, mainly for the “damage type” approach. Finally the numerical simulation of some experimental tests of corroded beam has been carried out
Constitutive model of concrete damaged by freeze–thaw action for evaluation of structural performance of RC elements
No full textThe coupled environmental-mechanical damage model extended by the authors to include the degradation effects on structural behavior of RC structures due to freezing-and-thawing cycles (FTC) is reformulated and generalized in the present work in order to better simulate the different aspects of the physical phenomenon. In particular the model is modified to consider separately the effect of FTC respectively on compressive and tensile strength and a new relationship to properly evaluate the equivalent number of FTC is proposed. To validate the model, an experimental campaign carried out on simply supported beams subjected to FTC is simulated. By comparing obtained numerical results with experimental evidence, the model is proved to be suitably accurate in reproducing the main aspects observed during tests: failure load, ultimate displacement, and failure mode. Actually the enhancement of freeze and thaw – mechanical model gives the base for the definition of a reliable numerical tool for analysis of RC structures subjected to FTC
Seismic risk mitigation technique for art objects: experimental evaluation and numerical modelling of double concave curved surface sliders
No full textThe opportunity and the advantages of applying base isolation technologies developed for civil structures to small objects are investigated and some considerations related to the scale effects are discussed. A series of experimental tests carried out at SRMD facility in San Diego are presented with the aim to investigate the dynamic response of a system designed to simulate a sculpture isolated by means of Double Concave Curved Surface Sliders. Such devices are specifically re-designed to fit the peculiar situation of light weight objects. In particular the samples used in the experimentation are designed with geometric and inertia characteristics fit for representing the Michelangelo’s sculptures exposed at the “Galleria dell’Accademia” in Florence, Italy. Finally, the main aspects concerning the numerical simulation of the seismic response of the proposed isolated system are discussed, also to investigate the efficiency of the existing numerical models, which are developed for traditional devices, when they are applied on such small and particular objects. The results of the experimental/numerical campaign show a general efficiency of the isolation system in terms of limiting the transferred action. Further study is needed to understand more clearly some local unexpected phenomena emerged from the experimental tests
A New Bond Degradation Model for Freeze-Thaw-Damaged Reinforced Concrete
No full textFreeze-thaw cycles (FTCs) are one the most serious causes of damage in RC structures in cold regions affecting both concrete and bond behavior. In this paper, after a comprehensive review on the effects on concrete and bond of freeze-thaw degradation for ordinary concrete, a new constitutive bond stress-slip law is formulated in the framework of a coupled mechanical-environmental damage model. This law is developed exploiting the versatility of Bezier curves and using an optimization process based on genetic algorithms to select the best form among some options (composite quadratic, composite cubic, and a single fourth-order curve). Moreover, a comprehensive enhanced freeze-thaw degradation (E-FTD) model is developed including the effect of FTCs on bond behavior, by means of a new environmental damage parameter included in the proposed bond stress-slip law. The whole model is formulated, calibrated, and validated referring to all the available experimental data to the authors' knowledge both for compressive and pull-out tests for ordinary concrete. The comparison with the experimental results showed the proposed E-FTD model is able to predict bond strength degradation fairly well and generally on the safe side, capturing also the overall bond-slip curves, making it particularly appealing for the structural analysis of RC elements subjected to FTCs according to an engineering-oriented approach
Structural risk assessment of corroding RC structures under seismic excitation
No full textDurability of reinforced concrete structures is a well known critical issue and civil engineers are aware of the need for durable design, as well as of the importance of maintenance, inspection and, if necessary, reparation/rehabilitation interventions. Furthermore, the assessment of RC constructions, especially of existing ones, is concerned with inevitable high uncertainties about geometry, material properties, applied loads and damage state, thus requiring a probabilistic approach for a reliable evaluation of the present and future performance. These issues become even more crucial in presence of natural hazards striking the structure, such as seismic excitations. In this paper, the major effects of aggressive environments on the seismic response of RC members are analyzed along with a probabilistic risk management procedure. In particular, a 4-steps methodology is developed to investigate the variation of the seismic behavior of a real case study over its service life, in presence of increasing degradation levels. Finally, the seismic risk associated with the long-term performance of the construction is calculated, providing a significant support in the implementation of efficient strategies for risk reduction
Rocking activation of free standing elements in real conditions: A safe experimentally-based acceleration limit
No full textThis paper presents an experimental campaign aimed to characterize rocking conditions of free-standing elements. Focus is given on the minimum horizontal acceleration required to activate rocking. The proposed experimental campaign mainly regards prismatic samples, that differ in size R (ranging from 6.30 cm to 23.0 cm), aspect ratio B/H (mostly 0.20 and 0.33) and material (wood, marble, steel). Small scale specimens are tested since no scale effect is expected in the rocking activation phenomenon. Both harmonic (continuous and pulse) and seismic input signals are applied for a total of more than three hundred tests. Experimental results evidence that, in most cases, rocking occurs for acceleration lower than the value generally assumed as the rocking limit, which is proportional, by acceleration gravity, to the aspect ratio. Therefore, a different value is proposed for the acceleration that triggers rocking phenomenon, with the aim of defining a safe acceleration threshold usable in vulnerability assessment of free standing elements. Actually, this limit takes into account the real conditions of rocking behavior, e.g. element imperfections, not perfectly rigid conditions for both block and supporting floor, not planarity of the contact surfaces
Seismic safety of valuable non-structural elements in RC buildings: Floor Response Spectrum approaches
No full textThe seismic performances of non-structural (NS) components belonging to the category of “valuable elements”, i.e. elements characterized by high value in terms of economic, cultural or strategic purposes, represent nowadays a crucial aspect in seismic safety design and assessment of new and existing buildings. Actually, most valuable NS elements are simply-supported objects, which can be classified as acceleration-sensitive NS elements. Frequently, these elements can be considered dynamically uncoupled from the primary structure to which they are connected, thereby justifying the Floor Response Spectrum methods usually adopted in literature and by most of building codes. This paper presents an extensive parametric study of floor response spectra obtained by linear and nonlinear numerical modeling of RC structures. Two sets of 30 horizontal ground motion scaled acceleration records are generated according to the Ultimate Limit State (ULS) and the Damage Limitation State (DLS) spectra adopted for building design. The numerical floor response spectra and those proposed by codes and international standards are critically compared, and the Peak Floor Acceleration (PFA) and the Peak Floor Velocity (PFV) profiles along the building height are discussed. Finally, a simplified method based on the “stability charts” is developed to assess the seismic safety of free standing NS elements located at the upper floors of the host building
Rischio sismico per beni artistici mobili: confronto tra differenti metodi di valutazione
No full textIn questo lavoro si propone il confronto tra valutazioni di vulnerabilità sismica di beni artistici mobili, in termini di oscillazione e ribaltamento, eseguite con diverse metodologie. Vengono in particolare presi in considerazione il metodo cinematico, lineare e non lineare, proposto dalla normativa italiana per l’analisi dei meccanismi di collasso, ed altri approcci di letteratura, che utilizzano quali parametri di riferimento per valutare la propensione al ribaltamento l’accelerazione, la velocità o lo spostamento. Il confronto tra le differenti metodologie di valutazione della stabilità globale è applicato ad un campione di indagine selezionato nell’ambito della Galleria dell’Accademia di Firenze: alcune grandi statue di marmo ed alcuni busti
An orthotropic damage model for non linear masonry walls analysis: irreversible strain and friction effects
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