Daniele Ferretti

Damage assessment of fortresses after the 2012 Emilia earthquake (Italy)

The medieval fortresses are a very common and distinctive type among the Emilian historical constructions and the earthquake of May 20 and 29, 2012 highlighted their high vulnerability. Starting from the analysis of the geometrical and constructive features, the interpretation of their seismic vulnerability has been based on an accurate damage assessment and supported by the numerical results of typical configurations. An abacus of recurring seismic damage mechanisms in fortresses has been proposed: it in particular concerns the towers and their interaction with the fortress perimeter walls. Moreover, the seismic response of the most important fortresses in the epicentral area has been described referring to their historical notes, the recent interventions and their influence on the seismic damage.

Non-linear model for R/C tensile members strengthened by FRP-plates

Abstract Transverse cracking in reinforced concrete (R/C) members strengthened by FRP plates and subjected to axial loads is analyzed. A non-linear model is developed, where cohesive stresses in concrete across cracks and non-linear bond–slip law between steel bars and concrete are used. The non-linear governing equations are solved via finite difference method. Comparisons with experimental results confirm the validity of the model. Numerical examples are also presented, simulating tests on plated and unplated R/C members with displacement, force, or crack opening control. The examples show that external FRP-plating is effective in reducing crack width and, consequently, in increasing axial stiffness of tensile members.

Analysis of damage mechanisms suffered by Italian fortified buildings hit by earthquakes in the last 40 years

This paper presents an empirical approach to studying the seismic behaviour of fortified buildings, including castles, fortresses, and citadels. The first step for a focused preventive intervention on this building typology, characterised by the presence of towers, defensive walls and other particular elements, is to identify recurring vulnerabilities. Over 750 castles and 7 seismic events which have hit Italy in recent decades have been considered, including the earthquakes in Central Italy in August and October 2016. For each seismic event, the characteristics of the earthquake have been described by means of shake maps, while the castles in the area have been identified and inserted in a specifically formulated geographic information system. Subsequently, a thorough archival and bibliographical research on the damage suffered by the most significant case histories allowed the comparison of the damage observed in the castles with different characteristics in terms of soil, materials, building typologies and conservation status. A previously proposed table of damage mechanisms was adopted and verified on a larger number of castles, suggesting some modifications. Lastly, statistical analysis on these data was conducted in order to inspect possible connections between building features, peak ground acceleration and damage mechanisms. The results have shown a good agreement with the existing vulnerability curve and the small amount of numerical analyses proposed in the literature for the same building typology.

A New Numerical Approach to the Structural Analysis of Masonry Vaults

The present paper concentrates on the numerical modelling of masonry vaults, adopting a type of analysis first developed at the University of Parma for applied mechanics, based on the use of non-smooth dynamics software, through a Differential Variational Inequalities (DVI) formulation specifically developed for the 3D discrete elements method. It allows to follow large displacements and the opening and closure of cracks in dynamic field, typical of the masonry vaulted structures. Once the modelling instrument was calibrated, thanks to the comparison with the recurrent damage mechanisms previously analysed, it was also applied to foresee the behavior of the same structure with different actions and with different types of strengthening. The development of damage mechanisms, both in quasi-static cases (for insufficient lateral confinement or for possible soil settlements) and in the occurrence of seismic events, make this type of structures very difficult to be modelled precisely with other methods. Given the three-dimensional CAD model of a vault modeled with a great number of masonry units with specific positions and pattern, the method proved to be able to reproduce the behavior of the structure under both static and seismic loads, showing the mechanism of collapse, the network of contact forces, the displacements and other useful data. The aim is to inspect the possible influences in the structural behavior given by the discrete geometry and the changes in the mechanisms development given by different strengthening interventions. Once the modeling instrument will be calibrated, also through the comparison with real cases and with the results obtained through limit analysis, it will be possible to adopt it as a base also for the prevision of the future behavior of the vaults subjected to strengthening, avoiding uncalibrated and uncritical applications of materials based more on trends rather than on a thorough analysis for the specific case.

Mechanical and Mineralogical Characterization of Mortar in Masonry Buildings Damaged by the 20-29th May Earthquake in Emilia

The aim of the work is to characterize mechanical and chemical properties of the mortar, and thus the masonry, of historical buildings damaged by the Emilia May 20-29th 2012 earthquakes. The attention was focused on historical strategic buildings, located in Modena district. The experimental campaign here reported was carried out for each building through four steps: first, a mechanical characterization of masonry was performed in situ using non-destructive and semi-destructive methods (step 1); then, some materials were collected in order to obtain standard specimens of mortar joint and brick (step 2). In laboratory, those samples were properly prepared for testing (step 3) with compression and flexural test setups; finally, a limited number of those mortar samples were tested in order to obtain their chemical properties (step 4). The in-situ and laboratory test results were separately elaborated for mortar and brick, to characterize the single masonry components. The results were then used to estimate the characteristic masonry parameters. Criteria to obtain the masonry behavior were reviewed in order to give the average masonry parameters. The characteristic and average values of compression strength were compared with ranges provided in the codes for the same masonry typology.

Investigation of Mode I fracture toughness of red Verona marble after thermal treatment

The present paper aims to assess the effect of freeze/thaw cycles on fracture behaviour of a natural stone: the red Verona marble. A wide variety of specimen types and methods to determine Mode I fracture toughness of natural stones are available in the literature and, in this context, the model originally proposed for plain concrete, i.e. the Two-Parameter Model (TPM), is adopted. Such a method is able to take into account the slow nonlinear crack growth occurring before the peak load, typical of quasi-brittle materials, with the advantage of easy specimen preparation and simple test configuration. In the present paper, the atmospheric ageing is simulated by means of thermal pre-treatments consisting of freeze/thaw cycles. Experimental tests are carried out using three-point bending Single-Edge Notched (SEN) specimens, according to the TPM procedure. The effects of thermal treatment on both mechanical and fracture parameters are examined in terms of elastic modulus and fracture toughness, respectively. KEYWORDS. Mode I Fracture Toughness; Red Verona Marble; Thermal Treatment; Two-Parameter Model.