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.

No abstract

In this Chapter we present the basic experimental facts on masonry materials and introduce simple and refined models for masonry. The simple models are essentially macroscopic and based on the assumption that the material is incapable of sustaining tensile loads (No-Tension assumption). The refined models account for the microscopic structure of masonry, modeling the interaction between the blocks and the interfaces.

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.

No abstract

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

No abstract