Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Parametric analysis on external dissipative link system for seismic protection of low rise r.c. buildings
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The seismic rehabilitation of existing r.c. and masonry buildings is a topical issue in Civil Engineering. A useful technique consists in the introduction of external bracing system. This kind of intervention can be improved throughout the introduction of dissipative links, here investigated with the help of some examples.. The links are made of common steel profiles: length, geometry and its disposition are considered as design parameters. A general procedure of link-bracing optimization is proposed applying a set of identical external restraints . The adopted dissipative links consent a cheaper and effective design both in terms of ULS than in DLS: the damages are addressed in a small area permitting an easy replacement of the links in case of earthquake.  
Analysis of the Fatigue Damage Behavior of AW2099-T83 Al-Li Alloy under Strain-Controlled Fatigue
No full textMicrostructural characteristics, monotonic and strain-controlled cyclic axial behaviors of AW2099-T83 Aluminum-Lithium alloy were investigated. Grain sizes and structures are not uniform in the different orientations studied. High strength and low ductility characterize the tensile behavior of the alloy under static loading. Strain-controlled fatigue testing was conducted at strain amplitudes ranging from 0.3% to 0.7%. Over this range, macro plastic deformation was only observed at 0.7%. Cyclic stress evolution was found to be dependent on both the applied strain amplitude and the number of cycles. Limited strain hardening was observed at low number of cycles, followed by softening, due probably to damage initiation. With low plastic strain, analytical approach was adopted to profile the damaging mechanism for the different applied strain amplitude. Because of the absence of fatigue ductility parameters due to low plasticity, a three-parameter equation was used to correlate fatigue life. Fractured specimens were studied under SEM to characterize the fracture surface and determine the controlling fracture mechanisms. The fractography analysis revealed that fracture at low strain amplitudes was shear controlled while multiple secondary cracks were observed at high strain amplitude. Intergranular failure was found to be the dominant crack propagation mode
Comparison of Two Parameters Models for clay brick masonry confinement
Get PDFMasonry elements are often strengthened in order to improve their structural capacity. Generalized methods to assess the behavior of confined masonry columns are not available in the technical literature. They have been usually derived from concrete confinement models. However, concrete and masonry present several crucial differences due to their physical and mechanical properties. In fact, generalized models to assess the axial capacity of masonry columns were limited by the strong variability and heterogeneity of physical and mechanical properties. However, the recent scientific researches provided relevant information on the experimental behavior of confined masonry columns. In this paper, a confinement model has been proposed to assess the axial capacity of clay brick masonry strengthened using several strengthening systems. The model has been validated by means of comparisons with experimental results. In order to assess the potential of the proposed model, the comparison was carried out also with other available mechanical models
3D limit analysis of masonry pavilion domes on octagonal drum subjected to vertical loads
Get PDFWithin the framework of limit design applied to masonry structures, this paper aims at analyzing the different behavior of a pavilion dome according to the adopted construction and reinforcement technologies. By using the static theorem applied to the dome discretized in rigid macro-blocks of variable shape aligned along parallels and meridians, a mathematical model have been constructed in order to search for the load collapse multiplier, and thus to evaluate the degree of structural safety. Then, the associated failure mechanism is represented at the instant in which the collapse is reached. The program that implement the modeling is sufficiently versatile and, in addition to the mechanical characteristics, allows to define the intrados profile, the thickness variability, as well as to insert any window opening in the drum, the lantern at the top and the hoops at each level. The results shown here concern some numerical applications carried out on a theoretical dome, as well as those related to a first approach to the analysis of the dome of Santa Maria del Fiore in Florence by Brunelleschi
Minimum energy strategies for the in-plane behaviour of masonry
Get PDFUnreinforced masonry is the most diffused construction material in the major part of historical centers in Europe. In a building subjected to earthquake forces the contribution of in-plane shear resistance of the masonry walls is a determinant factor for the stability of the whole structure. In particular, the masonry piers are the structural elements subjected to the combination of normal and shear forces. In general, ductile tools to model the in plane behaviour of masonry are always welcome in order to evaluate the capacity of walls subjected to vertical and horizontal actions. In this framework, two no-tension approaches to model the behaviour of masonry walls loaded with in-plane forces, involving a minimum energy procedure, are presented. Both the procedures allow the representation of the stress maps in the panel in case of monotonic increase of shear load. The results of the numerical analyses are compared and discussed
Influence of biochar additions on the fracture behavior of foamed concrete
Get PDFThe present study concerns the experimental investigation of foamed concretes with 1600 kg/m3 density that incorporate biochar additions in the mix. A series of small notched beams are prepared to determine the fracture energy in CMOD (crack mouth opening displacement) mode and the mechanical properties in terms of flexural and compressive strength. Besides the evaluation of such properties for classical foamed concrete, the influence of the addition of biochar in the lightweight cementitious paste is comparatively investigated. Two different concentrations of biochar are analyzed, namely 2% and 4% of the cement weight, and two different curing conditions are studied, namely in air and in water at controlled temperature for 28 days. The results demonstrate that better fracture behavior are obtained with 2% biochar and air curing conditions. The biochar additions in moderate concentrations (e.g. 2%) seems to make the fracture surface more tortuous, thus justifying the numerical outcomes, and does not impair the flexural strength. Further microstructural investigation is underway to confirm the experimental observations. This research paves the way for a promising construction material that is more environmentally friendly and sustainable than traditional materials used in the building industry
Micromodels for the in-plane failure analysis of masonry walls: Limit Analysis, FEM and FEM/DEM approaches
Get PDFIn the last decades the modeling of masonry structures has become an argument particularly appealing for many researchers and a large variety of numerical techniques have been formulated with the aim to produce practical applications in civil engineering, with special reference to the preservation and restoration of cultural heritage. Nevertheless, the question appears today still far from being resolved in a general way. The characteristics of frailty, heterogeneity and anisotropy of masonry, as well as the extreme variety of the building/construction rules strongly compromise the possibility of a unified description of its mechanical behavior.
In this work a comparison of different models and techniques for the assessment of the mechanical behavior of two-dimensional block masonry walls subjected to the static action of in-plane loads is presented. Different approaches and numerical models are considered: a Limit Analysis approach (LA), a FEM/DEM procedure and a non-linear heterogeneous Finite Element analysis (FE). In particular, the Limit Analysis is able to provide fast and reliable results in term of collapse multiplier and related mechanism. Here a standard Limit Analysis is adopted via a homemade procedure based on Linear Mathematical Programming, considering friction at interfaces. Analyses are performed referring to benchmark examples from literature
Behavior and damage of a pipe in the presence of a corrosion defect depth of 10% of its thickness and highlighting the weaknesses of the ASME / B31G method
Get PDFThe company DRC (pipe repair Department) located within the SONATRACH Company of oil and gas in Algeria, which is responsible for the repair of pipelines for the transport of gas or crude petroleum, will rehabilitate old pipes that have operated on-line for approximately 30 years or come from remaining projects. On the assumption that rehabilitating a pipeline means making it workable under the same conditions as a new structure and reducing the overall cost of the project. The abandonment of these tubes will have an important environmental and financial impact. The rehabilitation, which consists of recovering the maximum of tube, already used, therefore reduces the cost of the project. Inspection and evaluation of corrosion defects are carried out in accordance with ASME/31G method that is applied to low alloyed carbon steels with corrosion defects having soft profiles with low stress concentration.
Our research will consist in developing a method using a behavior-damage coupling of the material to highlight the weaknesses of the ASME / B31G method and show for defects whose depth does not exceed 10%, these defects can survive hydrostatic testing but will develop during service when the pressure is variable
Using DIC techniques to measure strain ranges inside the cyclic plastic zone ahead of a fatigue crack tip
Get PDFA stereo microscope coupled to a 3-D Digital Image Correlation system is used to measure strain ranges on the cyclic plastic zone ahead of a fatigue crack-tip. First, a very refined speckle pattern is applied on the surface of a disk-shaped compact tension specimen of 1020 low-C steel by spraying toner powder over a layer of white paint, a suitable technique to produce the very small dots needed to map surface strain loops on that small region. This technique can achieve enough resolution to measure elastoplastic strain ranges Δε near the crack tip, which cause damage accumulation inside the cyclic plastic zone as the crack grows. The applied technique can identify as well the effects of other nonlinear phenomena that happen in the near-tip region, such as crack closure. Therefore, such measurements can be used to verify the validity of the hypotheses behind the main fatigue crack growth models
Prediction of thermomechanical behavior of acrylonitrile butadiene styrene using a newly developed nonlinear damage-reliability model
Get PDFThe aim of this work was to evaluate the influence of temperature on the mechanical behavior of an amorphous polymer, namely acrylonitrile butadiene styrene (ABS), based on a series of uniaxial tensile tests on smooth specimens at different temperatures. The results demonstrate that the behavior of the polymers is strongly dependent on the temperature. Its influence on the physical characteristics during the study of polymer behaviors cannot be denied, particularly when the processes of shaping are investigated, which require significant contributions of heat and mechanical effort. For this reason, this study consists of predicting the evolution of ABS damage in two main zones. The first is the industrial zone, in which the configuration of macromolecular chains is largely immobile, and the temperature is below the glass temperature (Tg = 110°C). In this zone, a damage model based on the obtained experimental results allowed us to determine three stages of damage evolution, and then to specify the critical fraction of life, at which the material becomes unstable and defective, for the purpose of predictive maintenance. The second zone is that of thermoforming, in which the temperature is above the glass temperature, Tg. In this zone, the macromolecular chains tend to move more freely as the temperature increases. The same damage model was adopted to follow the flow process according to the fraction of life that represents the critical material parameter. This study also includes a comparison between the static (experimental) damage models and unified theory (theoretical) damage models