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

The interphase finite element

Mesomodelling of structures made of heterogeneous materials requires the introduction of mechanical models which are able to simulate the interactions between the adherents. Among these devices is quite popular the zero thickness interface (ZTI) model where the contact tractions and the displacement discontinuities are the primary static and kinematic variables. In some cases the joint response depends also on the internal stresses and strains within the thin layer adjacent to the joint interfaces. The interphase model, taking into account these additional variables, represents a sort of enhanced ZTI. In this paper a general theoretical formulation of the interphase model is reported and an original finite element, suitable for two-dimensional applications, is presented. A simple numerical experiment in plane stress state condition shows the relevant capabilities of the interphase element and allows to investigate its numerical performance. Some defects related to the shear locking of the element are resolved making use of well known numerical strategies. Finally, further numerical application to masonry structures are developed

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

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

Elastoplastic Damaging Model for Adhesive Anchor Systems. I: Theoretical Formulation and Numerical Implementation

In this and in the companion paper, the mechanical response of adhesive anchor systems is theoretically and numerically predicted and experimentally observed. The theoretical prediction is on the basis of an elastoplastic damaging model formulated to predict the structural response associated with the development of a fracture in adhesive anchor systems. This part describes the analytical model developed in the framework of a thermodynamically consistent theory, which assumes adhesion where the structure is sound, and friction in correspondence with the fracture. Isotropic damage is considered. The model can predict the structural behavior at the interface between two surfaces of ductile, brittle, or quasi-brittle materials. The Helmholtz free energy is written to model the materials' hardening or softening. Isotropic damage is considered, and the possible effects of dilatancy are taken into account, including nonassociative flow rules. The formulation is implemented into the finite-element code FEAP. In the companion paper, the new model is adopted to predict the mechanical response to the pullout force of postinstalled rebar chemically bonded in concrete. The analytical model and the numerical implementation are experimentally validated by several pullout tests, which are monitored by using an acoustic-emission technique

VALUTAZIONE DELLA RESISTENZA DI ADESIONE E DELLA LUNGHEZZA EFFICACE DI INCOLLAGGIO NEI GIUNTI ADESIVI TRAMITE LE LEGGI DELL’EFFETTO SCALA

In recent years, growing attention has been paid by researchers in structural mechanics to bonded joints in order to provide theoretical and numerical tools for better understanding the interfacial bonding/debonding phenomena. The research efforts in this area regard the formulation of reliable bond-slip models based on experimental data coming from laboratory tests performed on small specimens [1, 2]. As reported in [3], the mechanical quantities characterizing any interface constitutive law can be derived from the results of the experimental pull tests by a simple procedure making use of a schematization of the structural problem. The application to some single lap joint tests, carried out at the DISAG Laboratory of Palermo University, shows the effectiveness of the procedure