No abstract

In the present paper, we apply the theorems of limit analysis to vaults modeled as masonry-like materials, that is, unilateral continuous bodies. On allowing for singular stresses, we consider statically admissible stress field concentrated on surfaces lying inside the masonry. Such structures are unilateral membranes, whose geometry is described a la Monge , and the equilibrium of them, under vertical loads, is formulated in the Pucher form. The problem is reduced to pere roca a single partial differential equation of the second order where the shape f and the stress function F appear symmetrically. The unilateral restrictions require that the membrane surface lies in between the extrados and intrados surfaces of the vault and that the stress function be concave. Such a constraint is, in general, not satisfied on a given shape for given loads: in such a case, the shape has to be modified to fit the constraint. In a sense, the unilateral assumption renders the membrane an underdetermined structure that must adapt its shape in order to satisfy the unilateral restrictions. A number of simple examples are presented to illustrate how the method works

Masonry has historically been one of the most widely used construction materials. Despite this, there is a lack of computational tools for the analysis of masonry structures compared with what is available for steel and concrete structures. One of the main reasons is likely to be found in the peculiar mechanical behavior of masonry, which shows a small and unpredictable resistance in tension and a nonlinear inelastic behavior in compression. In this paper we put forward a constitutive model for masonry based on the extension to associate path-dependent plasticity of the classical normal, elastic, no-tension model. This new model allows the onset of fracture and irreversible crushing of the material and accounts for a wider variety of stress states within the structure, highlighting the progress of pseudorigid kinematics. The elastoplastic problem is decomposed into a sequence of nonlinear elastic problems formulated in variational form, which are solved by searching for the minimum of a suitable functional via descent methods. The model is implemented in variational finite element code and validated against analytical solutions and experimental tests. Applications to realistic cases are presented showing the capability of the model to reproduce nontrivial cracking and crushing patterns.

The idea of a no-tension (NT) material underlies the design of masonry structures since antiquity. Based on the NT model, the safety of the structure is a problem of geometry rather than of strength materials, in the same spirit of the “rules of proportion” of the medieval building tradition. The use of singular stress fields for equilibrium problems of NT materials in 2d, has been recently proposed by Lucchesi et al. to produce statically admissible stress fields; here we introduce a simple way to construct singular stresses, based on the Airy’s stress formulation. We interpret the singular part of such stress fields as axial contact forces acting on ideal 1d structures arising inside the body, in the same spirit of Strut and Tie methods. A number of simple problems of equilibrium concerning typical walls, arches and portals, is solved in terms of stress fields having regular and singular parts, by adopting the direct and the stress function formulation. The validity of the rules of proportion described by Derand and Gil is also verified

A few years ago, Anisakis infection was almost unknown. Since the first observation in the Netherlands in 1960, several cases of gastrointestinal infections due to a zoonosis sustained by this nematode have been described in countries in which the consumption of raw or uncooked fish (e.g., marinated or salted) is common. Japan alone accounts for 90% of all cases of anisakiasis described in the literature because of the widespread use of raw fish in traditional Japanese cuisine, with sushi and sashimi. Nonetheless, other cases have been reported in Europe, North and South America, and Asia. In Italy, this zoonosis is rare and mostly transmitted by the ingestion of marinated anchovies in coastal areas, or fashion foods (sushi, sashimi, etc.) in inland areas. Once eaten, this parasite can cause an acute form of disease characterized by severe abdominal pain, and for this reason many patients receive the final diagnosis only on obtaining the surgical specimen. Since conservative medical treatment for acute anisakiasis relies on endoscopic removal of the nematode from the gastrointestinal wall if performed within 12h from the ingestion of contaminated fish, it should be compulsory to consider this parasitosis in the accident and emergency department. Here we describe two cases of infection by Anisakis simplex due to ingestion of marinated anchovies in a coastal area of the Tyrrhenian Sea and discuss the types and varieties of Anisakis infection in humans.