INTERFACE MODEL FOR THE NONLINEAR ANALYSIS OF BLOCKY STRUCTURES OF ANCIENT GREEK TEMPLES

The presence of singularity surfaces with reference to the displacement field is a characteristic of a number of structural systems. Strong discontinuities are present in old masonry structures where dry joints connect the blocks or the mortar ageing suggests to neglect the adhesion properties. These structures cannot be considered a continuum but rather an assembly of blocks. These discontinuous structures could be modelled as an assembly of blocks interacting trough frictional joints whose mechanical behaviour is described by appropriate interface laws. In the present work an interface model present in literature is adopted, the double asperity model, which has been implemented in a standard finite element code with the principal aim to develop structural analysis of old monumental masonry structures. The interface model is briefly illustrated and the numerical implementation of the interface laws is described in detail. Numerical examples are presented to simulate the behaviour of a couple of greek temples of Agrigento Italy. These old monumental structures, IV-VI sec. BC, are inserted in the world heritage list by Unesco

An Hypervolume based constraint handling technique for multi-objective optimization problems

Formulation of structural optimization problems usually leads to the individuation of one or more objective functions to be minimized under different constraints. Many multi-objective evolutionary algorithms are approached by a Pareto-compliant ranking method, where no a priori information on the problem is needed and the concept of non-dominated solutions is used. In this paper a constraint handling technique based on the concept of hypervolume indicator is presented. Initially proposed to compare different multi-objective algorithms hypervolume indicator is the only single set quality measure to reflects the dominance of solution’s sets. The constraint handling technique proposed use an extension of stochastic ranking approach for single-objective optimization problem to multi-objective ones. The extension proposed use the hypervolume indicator to compares different solutions and is tested on a structural constrained multi-objective problems. Results show the suitability of the proposed approach

Damage identification by a modified Ant Colony Optimization for not well spaced frequency systems

Recently, it has been shown , that a damage detection strategy based on a proper functional calculated on the analytical signal of the structural dynamical response, consents to identify very low damage level. In this regard, they stressed the efficiency of Hilbert Transform to obtain the analytical response representation that shows more sensitivity for predicting damage with respect to the simple signal response. Then, a damage identification procedure based on the minimization of the difference between theoretical and measured data was proposed with satisfactory results. Unfortunately, this procedure, since the need of use of band pass filter around the natural frequency of the system, fails for structures having closed natural frequencies. By the way, performing procedures for sharply detecting damage in not well spaced frequency structure is a hoary problem. Aim of this paper is to extend the aforementioned procedure to these systems. To aim at this, it is desirable to go further insight into optimization algorithms, suitable for this kind of systems. For instance, it will be interesting considering, the ant colony optimization algorithm (ACO) that is a probabilistic technique for solving computational problems which can be reduced to finding good paths through graphs. Recently ACO has been extended to continuous domain and labeled as ACOð. A novel aspect of the proposed paper is introducing ACOð into the previous procedure avoiding the use of filters, such that may be available for not well spaced frequency system. Moreover, it will be desirable avoiding the use of Hilbert transform, that means apply the identification procedure directly on the acceleration responses and not on the analytical signal response. Therefore, in this paper it will be introduced a procedure for detecting damage in structures having close frequencies, without using analytical signal response

Heterogeneous structures studied by interphase elasto-damaging model.

For all structures that are constituted by heterogeneous materials, the meso-modelling approach is the most rigorous since it analyzes such structures as an assembly of distinct elements connected by joints, the latter commonly simulated by apposite interface models. In particular, the zero-thickness interface (ZTI) models are extensively used in those cases where the joint thickness is small if compared to the other dimensions of the heterogeneosu material. In ZTI models the constitutive laws relate the contact tractions to the displacement discontinuities at the interface, but in many cases the joint response depends also on internal stresses and strains within the bulkmaterial. In this sense the interphase model represents an enhancement of the ZTI because is able to introduce the effect of internal stresses into the analysis. Particular attention is spent to the definition of a damage model in order to describe the propagation of a fracture inside the interphase element. The damage model is developed in a thermodinamically context for plane stress applications

The interphase elasto-plastic damaging model

Heterogeneous materials present a mechanical response strongly dependent on the static and kinematic phenomena occurring in the constituents and at their joints. In order to analyze this kind of materials it is a common practice to distinguish a macroscopic length scale of interest from a mesoscopic one, where the mesoscopic length scale is of the order of the typical dimensions of the constituents. At the mesoscopic level the interaction between the units is simulated by mean of apposite mechanical devices. Among these devices is popular the zero thickness interface model where contact tractions and displacement discontinuities are the primary static and kinematic variables respectively. However, in heterogeneous materials the response also depends on joint internal stresses as much as on contact stresses. The introduction of internal stresses brings to the interphase model or an enhancement of the classical zero-thickness interface. With the term ‘interphase’ we shall mean a layer separated by two physical interfaces from the bulk material or a multilayer structure with varying properties and several interfaces. Different failure conditions can be introduced for the physical interfaces and for the joint material. The interphase model has been implemented in an open-source research-oriented finite element analysis program for 2D applications. Numerical simulations are provided to show the main features of the model

The interphase model applied to the analysis of masonry structures

Masonry material presents a mechanical response strongly dependent on the static and kinematic phenomena occurring in the constituents and at their joints. At the mesoscopic level the interaction between the units is simulated by means of specific mechanical devices such as the zero thickness interface model where the contact tractions and the displacement discontinuities are the primary static and kinematic variables respectively. In many cases the joint response depends also on internal stresses and strains within the interface layer adjacent to the joint interfaces. The introduction of internal stresses and strains leads to the formulation of the interphase model, a sort of enhanced zerothickness interface. With the term interphase we shall mean a layer separated by two physical interfaces from the bulk material or a multilayer structure with varying properties and several interfaces. Adopting the interphase concept, different failure conditions can be introduced for the physical interfaces and for the joint material. In the present work the interphase constitutive laws, taking into account the joint stiffness degradation and the onset of irreversible displacements, are derived in a thermodynamically consistent manner assuming an appropriate form of the Helmholtz free energy, function of the internal and contact joint strains and of other internal variables which regulate the evolution of the non-linear phenomena. The interphase model has been implemented in an open-source research-oriented finite element analysis program for 2D applications