A lumped stress method for plane elastic problemsand the discrete-continuum approximation

This paper proposes a rational method to approximate a plane elastic body through a latticed structure composed of truss elements. The method is based on the introduction of a relaxed stress energy that allows an extension of the original problem to a larger space of admissible stress fields, including stresses concentrated along lines. Use is made of polyhedral approximations of the Airy stress function. The truss analogy is employed to obtain a displacement formulation. The paper includes several numerical applications of the method to sample problems, a numerical convergence study and comparisons with exact solutions and standard finite element approximations

Application of the modified finite particle method to the simulation of the corneal air puff test

We present a numerical procedure for the simulation of the air puff test, a medical procedure used by ophtalmologists for the identification of the Intra Ocular Pressure, and potentially useful for the identification of material properties of the human cornea. The problem involves the modeling of the cornea, that is a biological tissue, modelled as an hyperelastic material, and the aqueous humor, that is, the fluid filling the anterior chamber of the eye, that is treated as a Newtonian fluid, and modelled using a meshfree formulation, useful for the solution of a Fluid-Structure Interaction problem. Fluid and Structure are coupled using a Dirichlet-Neumann iterative approach, which permits the adoption of a partitioned coupling approach and explicit, fast solvers for the different subproblems

Anisotropic constitutive equations and experimental tensile behavior of brain tissue

The present study deals with the experimental analysis and mechanical modeling of tensile behavior of brain soft tissue. A transversely isotropic hyperelastic model recently proposed by Meaney (2003) is adopted and mathematically studied under uniaxial loading conditions. Material parameter estimates are obtained through tensile tests on porcine brain materials accounting for regional and directional differences. Attention is focused on the short-term response. An extrapolation of tensile test data to the compression range is performed theoretically, to study the effect of the heterogeneity in the tensile/compressive response on the material parameters. Experimental and numerical results highlight the sensitivity of the adopted model to the test direction

Food safety in hospital: knowledge, attitudes and practices of nursing staff of two hospitals in Sicily, Italy

BACKGROUND: Food hygiene in hospital poses peculiar problems, particularly given the presence of patients who could be more vulnerable than healthy subjects to microbiological and nutritional risks. Moreover, in nosocomial outbreaks of infectious intestinal disease, the mortality risk has been proved to be significantly higher than the community outbreaks and highest for foodborne outbreaks. On the other hand, the common involvement in the role of food handlers of nurses or domestic staff, not specifically trained about food hygiene and HACCP, may represent a further cause of concern. The purpose of this study was to evaluate knowledge, attitudes, and practices concerning food safety of the nursing staff of two hospitals in Palermo, Italy. Association with some demographic and work-related determinants was also investigated. METHODS: The survey was conducted, by using a semi-structured questionnaire, in March-November 2005 in an acute general hospital and a paediatric hospital, where nursing staff is routinely involved in food service functions. RESULTS: Overall, 401 nurses (279, 37.1%, of the General Hospital and 122, 53.5%, of the Paediatric Hospital, respectively) answered. Among the respondents there was a generalized lack of knowledge about etiologic agents and food vehicles associated to foodborne diseases and proper temperatures of storage of hot and cold ready to eat foods. A general positive attitude towards temperature control and using clothing and gloves, when handling food, was shared by the respondents nurses, but questions about cross-contamination, refreezing and handling unwrapped food with cuts or abrasions on hands were frequently answered incorrectly. The practice section performed better, though sharing of utensils for raw and uncooked foods and thawing of frozen foods at room temperatures proved to be widely frequent among the respondents. Age, gender, educational level and length of service were inconsistently associated with the answer pattern. More than 80% of the respondent nurses did not attend any educational course on food hygiene. Those who attended at least one training course fared significantly better about some knowledge issues, but no difference was detected in both the attitude and practice sections. CONCLUSION: Results strongly emphasize the need for a safer management of catering in the hospitals, where non professional food handlers, like nursing or domestic staff, are involved in food service functions

Chap 4: Practical applications of unilateral models to masonry structures

This Chapter is devoted to the application of unilateral models to the stress analysis of masonry structures. Some 2d applications of what we call the simplified models for masonry, are discussed and studied. Though the essentially unilateral behaviour of masonry is largely recognized, some prejudices still persist on the possibility of making the No-Tension (NT) assumption a practical model for designing engineers. The results here presented demonstrate that the unilateral model for masonry can be a useful tool for modeling real masonry structures. In the exposition the critical points are emphasized and strategies to handle them are suggested, both for the most primitive model (namely the Rigid NT material), and for the more accurate Normal Elastic NT and Masonry-Like (ML)materials. The first tool here introduced for applying the No- Tension model to structures is the systematic use of singular stress and strain fields. Next a number of closed form solutions for NENT and ML materials is discussed. Finally a numerical approach based on descent is proposed for handling the zero-energy modes typical of unilateral materials. Some numerical solutions and comparisons with analytical solutions and test results are also presented

Static analysis of a Guastavino helical stair as a layered masonry shell

An analytical structural study of general helicoidal timbrel shells is presented. The study is concerned in particular with Guastavino staircases based on a circular planform. Such stairs are composite masonry structures formed by a two or three layers of tiles disposed in a herringbone-pattern. The analysis is based on the assumption that the material is unilateral, namely a No-Tension material in the sense of Heyman; in particular the safe theorem of Limit Analysis is employed. In the spirit of the safe theorem the structure is stable if a statically admissible stress field can be constructed; for the unilateral material here employed, singular stress fields, that is stress concentrated on surfaces (membranes) or lines (arches) are allowed. The statically admissible stress fields that are constructed, combining membrane stresses and 3d diffuse uniaxial stresses, are purely compressive and balance transverse loads either uniformly distributed or localized. A simple order-of-magnitude calculation confirm that bending and torsion resistance is small compared to the structural demand, and that a purely compressive membrane equilibrium stress field is required; the level of compressive stresses required to balance the load is below the limit compressive threshold

The Equilibrium of Helical Stairs Made of Monolithic Steps

An analytical structural study of helicoidal masonry stairs made of monolithic steps, built in torsionally at their external boundary, and supported on an inner rib, is presented. The results of the analysis are applied in particular to the case study of the triple helical stair of San Domingos de Bonaval. The analysis is based on the assumption that the material of the rib is unilateral, namely a no-tension material in the sense of Heyman; in particular the safe theorem of Limit Analysis is employed. In the spirit of the safe theorem the structure is stable if a statically admissible stress field can be constructed. For the unilateral material employed here, singular stress fields, that is stress concentrated on lines (arches) are allowed. The statically admissible stress fields here constructed, combining concentrated stresses and 2D diffuse uniaxial stresses, are purely compressive and balance the transverse loads