J. Toti

Interface Elements for the Analysis of Masonry Structures

The present paper deals with the modeling of the mechanical behavior of masonry elements regarded as heterogeneous systems, made of mortar and bricks joined by means of interfaces. The adopted computational strategy consists of modeling the brick units, the mortar joints and the interfaces responsible for the mortar-brick decohesion mechanisms; to this end, a special interface model combining damage and friction is adopted. A numerical procedure, based on the backward Euler time-integration scheme, is introduced; the time step is solved adopting a displacement driven predictor-corrector algorithm. Some numerical applications are performed in order to assess the ability of the proposed model and algorithm in reproducing the nonlinear response of masonry elements. Finally, unreinforced and FRP-reinforced masonry arches, for which experimental results are available, are modeled and the mechanical response is investigated. The results obtained by the numerical model are put in comparison with the experimental ones, showing the ability of the proposed model to simulate the behavior of the unreinforced and reinforced masonry arches in term of ultimate load, nonlinear behavior and collapse mechanism.

Modeling approaches for masonry structures

Different scale approaches, micromechanical, multiscale and macromechanical or phenomenological, are presented to study the structural response of masonry elements. First, a micromechanical model is introduced and the masonry is considered to be a heterogeneous material, made of mortar and bricks joined by interfaces, where the mortarbrick decohesion mechanisms occur. To this end, a special interface model combining damage and friction is proposed. Then, two multiscale procedures are presented, that consider regular arrangements of bricks and mortar, modeled by nonlinear constitutive laws which account for damage and friction effects. A homogenization technique is developed to derive two different equivalent continuum models at the macro-level, a micropolar Cosserat continuum and a nonlocal Cauchy model. Finally, a macromechanical model, based on the adoption of a classical No-Tension Material (NTM) model, and on the presence of irreversible crushing strains, is proposed. A zero tensile strength is assumed, thus fracture strains arise when the stress is zero. Moreover, an elastoplastic model is considered for the material response in compression. Numerical applications are performed on a masonry arch and two masonry panels, by adopting the three approaches presented. Comparisons with experimental outcomes, published elsewhere, are performed.

Ecosmart Reinforcement for a Masonry Polycentric Pavilion Vault

In the cultural life of modern societies great importance has acquired the preservation of existing and, in particular, ancient architectural heritage. With the inherent historical aspects, the economic implications have to be taken into account as well. Indeed, especially European cities and countries receive significant economic advantages by the existence of monuments and ancient suburbs. In this context, structural maintenance, strengthening and monitoring has gained an important academic and professional impulse. The present paper aims to present the results of a real scale experimental work regarding the application of an innovative seismic retrofitting technique for masonry walls and vaults by Hydraulic Lime Mortar strengthened by Glass Fiber Reinforced Polymer textile grids (HLM-GFRP) embedding new sensing systems as fiber optical sensors. The real scale specimen is a masonry polycentric pavilion vault that was damaged during the L’Aquila earthquake of April 2009. The need of eco compatibility of bonding material with masonry support implies the use of HLM-GFRP as strengthening system. On the other hand, the use of Fiber Bragg Grating (FBG) has a large number of advantages in opposite to electrical measuring methods. Example are: small sensor dimensions, low weight as well as high static and dynamic resolution of measured values, distributed sensing feature allowing to detect anomalies in load transfer between reinforcement and substrate and the location of eventual cracking patterns. A suitable Finite Element (FE) model is developed both to assess the effectiveness of the HLM-GFRP strengthening layers in retrofitting of the masonry vault and to define the strain field essential to the design of the FBG sensors network.

A coupled interface-body nonlocal damage model for the analysis of FRP strengthening detachment from cohesive material

In the present work, a new model of the FRP-concrete or masonry interface, which accounts for the coupling occurring between the degradation of the cohesive material and the FRP detachment, is presented; in particular, a coupled interface-body nonlocal damage model is proposed. A nonlocal damage and plasticity model is developed for the quasi-brittle material. For the interface, a model which accounts for the mode I, mode II and mixed mode of damage and for the unilateral contact and friction effects is developed. Two different ways of performing the coupling between the body damage and the interface damage are proposed and compared. Some numerical applications are carried out in order to assess the performances of the proposed model in reproducing the mechanical behavior of the masonry elements strengthened with external FRP reinforcements.

Seismic Retrofitting and Structural Health Monitoring of a Masonry Vault by using GFRP Grids with Embedded FBG Sensors

Fiber reinforced polymer (FRP) materials are currently used for strengthening of masonry structures. The behavior of this retrofit technique depends on the bond characteristics of the FRP to the external surface of the structure. A promising method to control the durability of the FRP reinforced structures is to incorporate fiber optical sensors (FOSs) in the composite material during its application or manufacture. The research leads to design of composite systems for the seismic retrofitting of an ancient masonry vault. The reinforcement technique involves the use of composite systems made up by FRP integrated with FOSs. The FOSs are employed as diagnostic tool for structural health monitoring. doi: 10.12783/SHM2015/202

Damage propagation in a masonry arch subjected to slow cyclic and dynamic loadings

In the present work, the damage propagation of a masonry arch induced by slow cyclic and dynamic loadings is studied. A two-dimensional model of the arch is proposed. A nonlocal damage-plastic constitutive law is adopted to reproduce the hysteretic characteristics of the masonry material, subjected to cyclic static loadings or to harmonic dynamic excitations. In particular, the adopted cohesive model is able to take into account different softening laws in tension and in compression, plastic strains, stiffness recovery and loss due to crack closure and reopening. The latter effect is an unavoidable feature for realistically reproducing hysteretic cycles. In the studied case, an inverse procedure is used to calibrate the model parameters. Then, nonlinear static and dynamic responses of the masonry arch are described together with damage propagation paths.

An approach for the modeling of interface-body coupled nonlocal damage

Fiber Reinforced Plastic (FRP) can be used for strengthening concrete or masonry constructions. One of the main problem in the use of FRP is the possible detachment of the reinforcement from the support material. This paper deals with the modeling of the FRP-concrete or masonry damage interface, accounting for the coupling occurring between the degradation of the cohesive material and the FRP detachment. To this end, a damage model is considered for the quasi-brittle material. In order to prevent strain localization and strong mesh sensitivity of the solution, an integral-type of nonlocal model based on the weighted spatial averaging of a strain-like quantity is developed. Regarding the interface, the damage is governed by the relative displacement occurring at bond. A suitable interface model which accounts for the mode I, mode II and mixed mode of damage is developed. The coupling between the body damage and the interface damage is performed computing the body damage on the bond surface. Numerical examples are presented.

Elementi di interfaccia per l’analisi di strutture murarie

The present paper deals with the modelling of the mechanical behaviour of masonry elements regarded as heterogeneous systems, made of mortar, bricks and interfaces. Thus, the adopted computational strategy consists in modelling the brick units, the mortar joints and the interfaces responsible for the mortarbrick decohesion mechanisms; to this end, a special interface model combining damage and friction is proposed. A numerical procedure, based on the backward Euler time-integration scheme, is introduced; the time step is solved adopting a displacement driven predictor-corrector scheme. Some numerical applications are performed in order to assess the performances of the proposed model and algorithm in reproducing the nonlinear response of masonry material due to damage localization. Finally, a masonry arch model is studied, comparing the numerical results with experimental ones; it is show the ability of the proposed model to simulate the global behaviour of the arch structure in term of ultimate load and collapse mechanism.