Antonio Tralli

A thermodynamically consistent nonlocal formulation for damaging materials

A thermodynamically consistent nonlocal formulation for damaging materials is presented. The second principle of thermodynamics is enforced in a nonlocal form over the volume where the dissipative mechanism takes place. The nonlocal forces thermodynamically conjugated are obtained consistently from the free energy. The paper indeed extends to elastic damaging materials a formulation originally proposed by Polizzotto et al. for nonlocal plasticity. Constitutive and computational aspects of the model are discussed. The damage consistency conditions turn out to be formulated as an integral complementarity problem and, consequently, after discretization, as a linear complementarity problem. A new numerical algorithm of solution is proposed and meaningful one-dimensional and two-dimensional examples are presented.

Damage assessment of fortresses after the 2012 Emilia earthquake (Italy)

The medieval fortresses are a very common and distinctive type among the Emilian historical constructions and the earthquake of May 20 and 29, 2012 highlighted their high vulnerability. Starting from the analysis of the geometrical and constructive features, the interpretation of their seismic vulnerability has been based on an accurate damage assessment and supported by the numerical results of typical configurations. An abacus of recurring seismic damage mechanisms in fortresses has been proposed: it in particular concerns the towers and their interaction with the fortress perimeter walls. Moreover, the seismic response of the most important fortresses in the epicentral area has been described referring to their historical notes, the recent interventions and their influence on the seismic damage.

AN UNSYMMETRIC STRESS FORMULATION FOR REISSNER-MINDLIN PLATES: A SIMPLE AND LOCKING-FREE RECTANGULAR ELEMENT

In the present paper a simple mixed-hybrid element for the linear analysis of Reissner-Mindlin plates is discussed. The element is derived from a modified Reissner functional and standard bilinear (isoparametric) interpolation for displacement and rotations is assumed whereas local stresses (rather than stress resultants and moments) are explicitly modelled. It is assumed that in plane shear stresses are not a priori symmetric. This choice allows to decouple the equilibrium equations, and involves introducing an in-plane infinitesimal rotation field, corresponding to drilling degrees of freedom. Out-of-plane shear stresses are then obtained such that equilibrium equations are exactly satisfied. The proposed element does not exhibit locking effects at all: i.e. the shear deformation energy is zero in the thin plate limit. Details of the formulation are provided, and the performances of the element are assessed with reference to well-established benchmark problems.

Computational Methods for Masonry Vaults: A Review of Recent Results

The present paper makes a critical review of some methods and models, now available in the technical litera- ture and commonly used in the analysis of masonry vaults up to their collapse, by highlighting advantages and drawbacks of each approach. All methods adopted to describe the mechanical behavior of masonry structures, in order to be reliable, must take into account the distinctive aspects of masonry, namely the scarce (or zero) tensile strength, the good resistance in compression and the occurrence of failure mechanisms through rotation-translation of rigid macro-blocks. Classic no- tension material models disregard the small existing tensile strength and make the assumption of (1) infinitely elastic be- havior in compression and (2) isotropy, giving thus the possibility to deal with either semi-analytical approaches (espe- cially for arches) or robust numerical procedures. More advanced but rather complex models are nowadays able to deal al- so with anisotropy induced by texture, small tensile strength and softening in tension, as well as by finite strength in com- pression. Traditionally - and nowadays it is still an opinion commonly accepted, in contrast with step by step complex procedures, Limit Analysis has proved to be the most effective Method for a fast and reliable evaluation of the load bear- ing capacity of vaulted masonry structures: classic lower and upper bound theorems recall respectively the concepts of equilibrium and occurrence of failure mechanisms with rigid elements. The so-called Thrust Network Method moves its steps from lower bound theorems, whereas FE limit analysis approaches with infinitely resistant elements and dissipation on interfaces take inspiration from the upper bound point of view. An alternative to Limit Analysis is represented by tradi- tional FEM combined with either elastic-plastic or damaging models with softening, commonly used for other materials but recently adapted also to masonry. They are able to provide a large set of output numerical information but further studies are still needed to ensure their proper application.

ArchNURBS: NURBS-Based Tool for the Structural Safety Assessment of Masonry Arches in MATLAB

AbstractA new approach toward a fully computer-aided design (CAD) integrated structural analysis of arched masonry structures is proposed and a new MATLAB-based computational tool, named ArchNURBS, is developed. It is addressed to professionals dealing with the restoration or structural rehabilitation of historical constructions, who need to assess the safety of masonry arches under assigned load distributions. By using it, they can easily produce estimates of the carrying capacity of curved masonry members, and specifically arches of arbitrary shape. A CAD environment, which is very popular among professionals, can be employed to provide a nonuniform rational B-splines (NURBS) representation of arch geometry. On the basis of this representation, it is possible to perform both an elastic isogeometric analysis and a limit analysis of the structure up to the collapse load. Moreover, the developed tool is devised for handling the presence of fiber-reinforced polymers reinforcement strips at the extrados and/...

Numerical insights on the seismic behavior of a non-isolated historical masonry tower

In this paper, numerical insights on the seismic behavior of a non-isolated historical masonry tower are presented and discussed. The tower under study is the main tower of the fortress of San Felice sul Panaro, a town located near the city of Modena (Italy). Such a tower is surrounded by adjacent structural elements and, therefore, is not isolated. This historical monument has been hit by the devastating seismic sequence occurred in May 2012 in the Northern part of the Emilia region (the so-called “Emilia earthquake”), showing a huge and widespread damage. Here, in order to understand the behavior of the structure, its interaction with the adjacent buildings and the reasons of the occurred damage, advanced numerical analyses (both nonlinear static and dynamic) are performed on a 3D finite element model with different levels of constraint supplied by the adjacent structural elements and a detailed comparison between the simulated damage and the actual one is carried out. The results of the conducted numerical campaign show a good agreement with the actual crack pattern, particularly for the model of the tower that considers the adjacent structural elements.

Design of a crystalline undulator based on patterning by tensile Si3N4 strips on a Si crystal

A crystalline undulator consists of a crystal with a periodic deformation in which channeled particles undergo oscillations and emit coherent undulator radiation. Patterning by an alternate series of tensile Si3N4 strips on a Si crystal is shown to be a tractable method to construct a crystalline undulator. The method allows periodic deformation of the crystal with the parameters suitable for implementation of a crystalline undulator. The resulting periodic deformation is present in the bulk of the Si crystal with an essentially uniform amplitude, making the entire volume of the crystal available for channeling and in turn for emission of undulator radiation.

Fast Kinematic Limit Analysis of FRP-Reinforced Masonry Vaults. I: General Genetic Algorithm–NURBS–Based Formulation

AbstractA new approach for the limit analysis of masonry vaults retrofitted with fiber-reinforced polymers (FRP) based on an upper bound formulation is presented in this paper. In particular, a new...

Fast Kinematic Limit Analysis of FRP-Reinforced Masonry Vaults. II: Numerical Simulations

AbstractA new approach for limit analysis of masonry vaults retrofitted with fiber-reinforced polymers (FRPs) based on an upper bound formulation is presented. Part I of this paper was devoted to d...

Buckling of Timoshenko Beams in Frictionless Contact with an Elastic Half-Plane

AbstractThis paper deals with the buckling analysis of Timoshenko beams of finite length in frictionless contact with an elastic substrate in a generalized plane stress or plane strain regime. The proposed FEM makes use of a mixed variational formulation based on the boundary integral equation commonly referred to as the Flamant solution. The corresponding finite-element model for the soil-structure interaction system adopts two-node locking-free finite elements for the Timoshenko beam and a constant soil reaction underlying each foundation element. Significant cases are thoroughly discussed, and a classical two-dimensional finite-element model is developed to have reference solutions. Numerical examples show that the proposed model is very simple and effective, and the Timoshenko beam model appears to be very useful in determining buckling loads in good agreement with reference solutions. Conversely, the Euler-Bernoulli beam model provides satisfactory results for long beams on soft soil only.