Papers by Author: Bernardino Chiaia

Abstract: The conventional framework for Structural Health Monitoring (SHM) primarily focuses on individual structures. However, to effectively identify the most vulnerable elements, preliminary studies are required at a wide area scale. This becomes particularly challenging in urban settings, where numerous buildings of varied shapes, ages, and structural conditions are closely spaced from one another. A twofold task is therefore required: the automated identification and differentiation of various structures, coupled with a ranking system based on perceived structural risk, here assumed to be linked to their deformation patterns. It integrates displacement measurements acquired through the Differential Synthetic Aperture Radar Interferometry (DInSAR) technique, specifically employing the full-resolution Small Baseline Subset (SBAS) approach, with Hierarchical Clustering. The effectiveness of this method is successfully demonstrated and validated in two selected areas of Rome, Italy, serving as case studies. The results achieved on this wide area scale monitoring can be used to select the constructions that need a more in-depth assessment.

Abstract: The paper aims to analyse the e ects of topography and building position on themagnitude of pressure exerted by snow avalanches against buildings, through a structural backanalysis and numerical uid-dynamics. Studying a real snow avalanche impact occurred in2008 which destroyed a village in Valsavarenche (Aosta Valley - IT), the attention is focused onthe avalanche ow deviation caused by the destructive interaction with a rst building, whichprotected part of a second building beyond it. By means of photographical and in situ survey,a detailed description of avalanche geometrical, dynamical and physical properties is outlined.A structural investigation, based both on debris arrangement and on measurements on theundamaged parts of buildings is also carried out.Thus, a back analysis is carried out in order to de ne collapse dynamics and to estimate theupper and the lower bound of impact pressure. Afterwards, numerical uid-dynamical analysesare performed to simulate di erent impact scenarios and to understand the e ects of obstacleson avalanche behavior: a qualitative measure of the interactions among buildings, which maymutually protect one another, is obtained.

Abstract: We analyze the distribution of grains in solid cubes of ice in terms of deterministic and stochastic 3d fractal models. We argue that the fractal dimension D or the Hurst exponent H optimally describe the void distribution in the snow sample and can be used as a parameter to describe the mechanical properties of snow at different scales.

Abstract: An energy-based criterion is introduced in order to investigate the nonlinear dynamic response of RC beams subject to rapid and unexpected damages. Since only static pushover analysis is necessary, the structural behavior of the damaged members can be evaluated with a new simplified procedure. It is firstly applied to the case of elastic–perfectly plastic continuous beam, when one of the supports is quickly removed. In such a situation, the proposed procedure gives satisfactory results if compared to those of a more rigorous dynamic analysis. By means of a nonlinear static analysis, which encompasses also the post-peak response, the energy-based approach is also applied to concrete beams. More specifically, it is used to predict the bearing capacities of reinforced concrete beams, having different steel rebars, when they suddenly lose a single support.

Abstract: The mechanical model of a number of biological tissues is a membrane, i.e., a sheetlike structure with small thickness, where deformation and stress can be described locally in two dimensions. Many bio-membranes, particularly if subjected to large mechanical loads, present a fibrous structure, with stiff fibers, sometimes with preferential orientations, embedded in a more compliant matrix. Among this tissues are, e.g., the arterial walls, the amniotic membrane, and the skin. The stiff fibers, typically made of collagen, are initially wrinkled and they follow the deformation of the embedding matrix without contributing to the mechanical response until they are fully distended. In this paper, the response of a fibrous membrane is described in the framework of hyperelasticity, with aim to the implementation in an existing finite element code. A micro-mechanical recruitment model, based on the statistical distribution of the activation stretch of the collagen fibers is introduced, leading to the definition of a simple form of the strain-energy function, depending on physically well-defined parameters. After some validation tests performed in homogeneous strain conditions, an application to the study of the stress field around circular holes in large deformation is presented, showing the capabilities of the proposed model.

Abstract: The apparent shear strength of rock discontinuities is lower than that of small scale samples. At the same time, the sliding behavior is characterized, in situ, by marked instabilities. Numerical algorithms permit to calculate contact forces at any point, and to describe the stick-slip transition. On the other hand, the critical aspects are not captured by classical theories. Multiscale simulations show that the contact domain between rough surfaces is a lacunar set. This explains the size-dependence of the apparent friction coefficient. By applying an increasing tangential force, the regime of partial-slip comes into play. However, the continuous and smooth transition to fullsliding predicted by the Cattaneo-Mindlin theory is not occurring in real situations. We implement a numerical renormalization group technique, taking into account the redistribution of stress consequent to partial-slip. This permits the critical value of the tangential force to be found. The critical force is less than the one predicted by Coulomb’s theory, and depends on the specimen size and on the topology of the interface.