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Mesomodelling of structures made of heterogeneous materials requires the introduction of mechanical models which are able to simulate the interactions between the\ud 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\ud thin layer adjacent to the joint interfaces. The interphase model, taking into account these additional variables, represents\ud 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\ud element are resolved making use of well known numerical strategies. Finally, further numerical application to masonry structures are developed

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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.

This paper presents a study on the use of acoustic emission (AE) to assess the structural soundness of concrete reinforced with chemically bonded anchors. The results of an experimental work based on six pullout tests monitored using an AE instrumentation suite are reported below. In every test one rebar was embedded in the hardened concrete by means of polyester resin. The AE was adopted to moni- tor the onset and progression of any structural damage. The parametric analysis, the intensity analysis and the moment tensor analysis of AE data were used to discriminate among different sources of damage. The technique shows promise for field application and may contribute to fully understand the structural mechanism in the rebar/adhesive/concrete sys- tems