No abstract

Correct estimate of curvature ductility of reinforced concrete members has always been an attractive subject of study as it engenders a reliable estimate of capacity of buildings under seismic loads. The majority of the building stock needs structural assessment to certify their safety under revised seismic loads by new codes. Structural assessment of existing buildings, by employing nonlinear analyses tools like pushover, needs an accurate input of moment-curvature relationship for reliable results. In the present study, nonlinear characteristics of constitutive materials are mathematically modelled according to Eurocode, currently in prevalence and analytical predictions of curvature ductility of reinforced concrete sections are presented. Relationships, in explicit form, to estimate the moment-curvature response are proposed, leading to closed form solutions after their verification with those obtained from numerical procedures. The purpose is to estimate curvature ductility under service loads in a simpler closed form manner. The influence of longitudinal tensile and compression steel reinforcement ratios on curvature ductility is also examined and discussed. The spread sheet program used to estimate the moment-curvature relationship, after simplifying the complexities involved in such estimate, predicts in good agreement with the proposed analytical expressions. Avoiding somewhat tedious hand calculations and approximations required in conventional iterative design procedures, the proposed estimate of curvature ductility avoids errors and potentially unsafe design

The proposal of the present work is to furnish a general approach to construct exact elastic solutions for FGM cylinders, made of a central core and n arbitrary cylindrical hollow homogeneous and isotropic phases. The hypothesis of axis-symmetrical boundary conditions is here assumed in order to analyze a class of elastic problems which present no-decaying of selected mechanical quantities and in particular of the axial strains ε 33 in the radial direction, being x 3 the axis of the laminated cylinder. To construct a robust mathematical procedure for obtaining exact elastic solutions for axis-symmetrical n-plies-Functionally Graded Material Cylinders (n-FGMCs), a theorem is first given for qualifying the space of the solutions and then their mathematical form is identified, when the object exhibits no-decaying of the axial strain. By starting from the classical Boussinesq-Somigliana-Galerkin vector and specializing it to torsionless composite cylinders characterized by no-decaying of the axial strain, a special form of the bi-harmonic Love's function χ (i) (r, x 3 ) is finally obtained. It is then demonstrated that the differential boundary value problem (BVP) always can be translated in an equivalent linear algebraic one, first solving an in cascade one-dimensional Euler-like differential system (field equations) and then writing the boundary conditions by means an algebraic system ruled by a (6n + 4)-order square matrix P. At the end, constructive and existence theorems are formulated and proved, showing examples in comparison with literature data.

In a.d. 79, the catastrophic eruption of Vesuvio, which later was described in two famous letters by Pliny the Younger to Tacitus the Historian, destroyed Pompeii, Hercolaneum, Oplontis and Stabiae, resulting in many thousand of victims. After a few hours of the eruption, the several-kilometre-high volcanic column began to collapse, provoking strong air shocks as well as destructive pyroclastic density currents, which travelled down the volcano slopes. In 2000, an archaeological excavation survey, which was performed on the east slope of the volcano in the Terzigno-Vesuvio area at a distance of about 5 km from the vent, brought to light the ruins of several Roman villas that were completely destroyed by these currents during the a.d. 79 eruption. The present paper proposes a new structural analysis, which starts from the study of the damage produced on partially collapsed masonry walls, and determines the dynamic pressures of the currents that overran this site. The nonlinear structural analysis, which is based on strength values obtained by means of experimental tests, is of the 'inverse type' and takes into account the limit behaviour of the ancient Roman masonry. The values of the dynamic pressures that were capable of producing the collapse of the masonry walls were obtained by utilising a modern limit analysis theory. The obtained results show that dynamic pressures of a few kPa (1-5) were able to cause masonry buildings to collapse. These values are consistent with those proposed in some of the latest volcanological studies made by numerical simulations of pyroclastic flow propagation. It is shown here that these dynamic pressures are even able to determine the collapse of both modern reinforced concrete and masonry wall buildings that are largely present in the area. Therefore, in possible future eruptions, dynamic pressures of this magnitude would flatten a large urbanised area, where~700,000 people are currently living. The obtained results give a better definition of both the risk to pyroclastic currents in possible Vesuvio eruptions and provide new guidelines for construction in the neighbouring zones.

In recent years the use of distributed optical fiber sensors for measurements of strain in beams, by means of the Brillouin scattering effect, has been proposed. Several works pointed out the practical difficulty of this kind of measurement, connected both to theoretical and to experimental problems, e.g. mechanical characterization of optical fibers, decaying of strains in the protective coatings, spatial resolution of the Brillouin scattering, brittleness of the glass core, elastic–plastic response of the polymeric jackets, end effects and the different responses of the fiber for dilatation and contraction. Dealing with each of the above problems still requires a great research effort. However, recent literature shows that distributed optical fiber measurement techniques are extremely useful for finding qualitative responses in terms of strains. Indeed, in spite of the above-mentioned uncertainties, the great advantage of the proposed distributed measurement of strains remains evident for the safety assessment of large structures, such as bridges, tunnels, dams and pipelines, over their whole lifetimes. In view of this, in the present paper the detection of defects or damage in bending beams—by using distributed optical fiber sensors in a method based on time domain stimulated Brillouin scattering—is proposed. In particular, laboratory tests were carried out to measure the strain profile along a steel beam. Two tests were performed: the first one involves an integral steel beam, while the second experiment is performed on a damaged beam. Comparison between these two tests allows the detection of the position and the establishing of bounds on the size of the defect. At the end, the quality and accuracy of the measurements are discussed and a sensitivity analysis of the strain readings taking into account the bonding conditions at the interface between the structure and the fiber is also carried out by means a parametric numerical simulation.

No abstract

No abstract

No abstract