Mariateresa Lombardo

Stochastic Modeling of Chaotic Masonry via Mesostructural Characterization

The purpose of this study is to explore three numerical approaches to the elastic homogenization of disordered masonry structures with moderate meso/macrolengthscale ratio. The methods investigated include a representative of perturbation methods, the Karhunen-Lo eve expansion technique coupled with Monte-Carlo simulations and a solver based on the Hashin-Shtrikman variational principles. In all cases, parameters of the underlying random eld of material properties are directly derived from image analysis of a real-world structure. Added value as well as limitations of individual schemes are illustrated by a case study of an irregular masonry panel.

Elastic wave dispersion in microstructured membranes

The effect of microstructural properties on the wave dispersion in linear elastic membranes is addressed in this paper. A periodic spring-mass lattice at the lower level of observation is continualized and a gradient-enriched membrane model is obtained to account for the characteristic microstructural length scale of the material. In the first part of this study, analytical investigations show that the proposed model is able to correctly capture the physical phenomena of wave dispersion in microstructured membrane which is overlooked by classical continuum theories. In the second part, a finite-element discretization of microstructured membrane is formulated by introducing the pertinent inertia and stiffness terms. Importantly, the proposed modifications do not increase the size of the problem compared wiith classical elasticity. Numerical simulations confirm that the vibrational properties are affected by the microstructural characteristics of the material, particularly in the high-frequency regime.

Performance-based seismic analysis of light SDoF secondary substructures

A novel procedure is presented for the application of the PBE (performance-based engineering) methodology to the seismic analysis and design of light secondary substructures. In the proposed technique, uncertainty is conveniently represented in the reduced modal subspace rather than geometric domain, which significantly reduces the number of uncertain parameters. The random response of a primary structure under earthquake excitation is investigated, various cases of linear and nonlinear secondary subsystems are examined and the propagation of uncertainty from the dynamic properties of the primary structure to the seismic performance of the secondary subsystems is quantified.

Stochastic analysis of fractional oscillators by equivalent system definition

Fractional oscillators have been recently proposed as damping devices under the configuration of Fractional Tuned Mass Dampers (FTMD), realized by connecting an oscil- lating mass to the primary structure through a viscoelastic link with inherent fractional con- stitutive law. The characteristic tuning frequency for the FTMD has been identified with the Damped Fractional Frequency (DFF), defined as the frequency at which the squared abso- lute value of the transfer function of the device attains its relative maximum. The definition of the DFF constitutes an interesting step towards the analysis of fractional oscillators in the frequency domain. In this paper, a simplified frequency domain approach is presented for the design of fractional oscillators subjected to stationary white noise. The analysis of the frac- tional oscillator is performed by using an equivalent single degree of freedom system with linear viscous damping. The aim is to obtain a clear understanding of the physical dynamic effects of the variations in the fractional oscillator parameters, in terms of damping and natu- ral frequencies. Moreover, the use of an equivalent system allows for the straightforward ap- plications of stochastic analysis to determine an approximate closed-form expression of the response variance.