168 research outputs found
An introduction to the regional Italian project ProSisMu devoted to the seismic protection of ancient masonry structures
No full textProSisMu (acronym of the Italian translation of Seismic Protection of Masonry structures) is an Italian project ideated by the synergy of the ERREGI group, a company which works in the civil and architectural engineering field, and the scientific contribution of the University of Rome Sapienza, Department of Structural and Geotechnical Engineering, recently approved to be financed by the regional finance company FILAS, Lazio Italy. The problem of seismic protection of historic masonry structures is always current in Italy, a country reach of history and of an extensive cultural heritage. The tragic seismic events happened in this territory, the last significant one refers to the L'Aquila earthquake in April 2009, together with the necessity of restoration and preservation of the cultural heritage, faced the necessity of a systematic analysis of the kind of structural damages induced on masonry structures. This work aims to illustrate the program of the project which shall be realized in the next two years. © 2012 IEEE
Masonry walls as orthotropic no tension structures
No full textIn this paper, following the research line proposed by Signorini (1925) and previously by
Milankovicth (1910), a semi-analytical approach for the analysis of masonry walls - treated as
horizontally multi-layered strata of no-tension material - is proposed in order to evaluate the stress
distribution generated by applied loads. The main applications concern walls subjected only to
vertical loads, although it is assumed that a constitutive friction relationship is guaranteed along the
horizontal joints, in the presence of horizontal actions. The goal is to identify in the masonry wall the
actual bearing sub-structures by defining at each vertical and horizontal level the transversal sections
generated by the unilateral behaviour. The method proposed will allow identifying the partition of the
wall into macro elements, which depend on the centre of applied loads, and wall and bricks
geometrical features. The technique adopted to approach the problem can be referred to as the search
for the best shape. Two cases are discussed: corbelled masonry wall surrounding windows and arch
behaviour of masonry over the window
On the behaviour of ancient masonry structures subjected to static loads: Case studies
No full textThe paper deals with the mechanical behaviour of ancient masonry constructions subjected to static vertical loads. The cases considered concern structures designed to cover a given span. Masonry is modelled as a no-tension orthotropic. Three cases are analysed. The purpose of the study is to recognise for each case the bearing structure. As a consequence of the modelling the masonry is divided into macro-elements separated by possible fracture lines which define the starting of probable regions where damage can be localised
Controllo semi attivo di strutture adiacenti mediante dispostivi magnetoreologici: teoria, sperimentazione e modellazione
No full textIn questa tesi si sono invece affrontati, gli aspetti legati alla teoria,
sperimentazione e modellazione di sistemi strutturali controllati mediante
dispositivi semi attivi MR.
Partendo da una sommaria panoramica dello stato dell’arte sul controllo
semi attivo (Capitolo 2) e delle applicazioni riferite a differenti problemi
strutturali, principalmente nel settore dell’ingegneria civile, si è poi inteso
approfondire l’analisi dei dispositivi semi attivi, capaci di variare in tempo
reale le proprie caratteristiche meccaniche per mezzo di un algoritmo di
controllo.
Il Capitolo 3 è focalizzato sulla descrizione di una specifica classe di dispositivi
semi attivi, i dispositivi magnetoreologici (MR). Sono descritte le
interessanti proprietà che possiedono i fluidi MR che costituiscono l’elemento
peculiare del dispositivo, il loro principio di funzionamento, gli aspetti
legati alla modellazione reologica e, infine, le numerose applicazioni che essi
trovano in diversi campi dell’ingegneria.
Nel Capitolo 4, al fine di chiarire l’importanza di un algortimo nell’impiego
di sistemi di controllo semi attivo, sono richiamati i fondamenti
della teoria del controllo, legandoli ai concetti di stabilità ed ottimalità.
Successivamente, sono descritte alcune tecniche di progetto del controllore,
dalle quali vengono ricavati degli algoritmi noti di letteratura. Dalla teoria
del controllo ottimo, in particolare, è ricavato l’algoritmo di controllo che è
stato utilizzato nella sperimentazione dinamica su tavola vibrante. Infine gli
algoritmi selezionati sono applicati in un esempio illustrativo (telaio a quattro
gradi di libertà con controvento elastico e dispositivo MR posto al primo
piano) volto a chiarire gli aspetti computazionali e a valutarne l’efficacia
A semi-analytical approach for the contact dynamics of ancient columns modeled as rigid blocks
No full textThe problem of conservation and protection of
architectural heritage against dynamic inputs such as the case
of earthquakes has represented for years an important task in
the field of structural engineering with the aim of describing
and understanding the behaviour of monumental structures.
This work deals with monumental structures made of large
and heavy stone blocks, simply supported to each other, a
typical technology used to build the Greek temples. The plane
dynamics of a rigid rectangular block simply supported on a
horizontally moving ground, with friction and unilateral
constraints at ground contact, is modeled by means of a new
semi-analytical approach for non-smooth contact dynamics
recently developed by one of the authors [1]. The dynamics -
formulated as a contact problem governed by Signorini’s and
Coulomb’s laws - is converted into an equivalent problem of
static balance by making use of specific projective techniques
in the configurations space. The procedure is then applied to a
numerical model, so that a code can be implemented where the
dynamics of the block is fully modeled according to the various
possible mechanisms considering both phases of smooth and
non-smooth contact dynamics; moreover normal and
tangential contact reactions during smooth dynamics, and
corresponding impulses during non-smooth, are estimated at
each step. Either extended or single point contacts are then
possible with consequent sliding, rocking or sliding-rocking
modes, so as the possibility of impacts and also of free
dynamics when contact is lost. Analyses are conduced and then
compared to corresponding cases previously treated in
literature, in order to validate the proposed numerical method
for the rocking mode. Moreover, dynamic evolution of the
block is represented graphically in order to observe different
configurations at each instant of time. The goal is to
understand the dynamic behaviour of the block under several
input intensities in order to prevent excessive sliding or
overturning and to localize with sufficient precision the
position of the block after the earthquake
Seismic simulation and base sliding of concrete gravity dams
No full textA simplified procedure to estimate possible base sliding of concrete gravity dams induced by an earthquake is proposed on the basis of results obtained by parametric analysis. A simple mechanical model is developed to take into account the most relevant parameters influencing seismic response such as dam-water and dam-foundation interaction. In order to catch base residual displacement, a threshold value for the sliding foundation resistance is fixed. The dam is modelled as an elastic linear single degree of freedom system. The hydrodynamic effects of the water in the reservoir are taken into account with generalized supplementary mass and force as well as by adding supplementary damping. The foundation resistance is modelled with the Mohr-Coulomb criterion including a frictional and a cohesive component and the presence of a passive wedge resistance is also considered. A comprehensive numerical analysis of the response of concrete gravity dams subjected to several natural earthquake records relative to events mainly happened in Italy is carried out to estimate base residual displacement. Different parameters are considered in the analysis such as dam height, foundation rock parameters, water level, seismic intensity. As a result a simplified methodology is developed to evaluate base residual displacement, once known dam geometry, response spectrum of the seismic input, and the soil characteristics. The procedure permits to assess seismic safety of the dam with respect to base sliding, as well as water level reduction necessary to render the dam safe enough
A simplified procedure to estimate base sliding of concrete gravity dams induced by an earthquake
No full textIn this study a simplified procedure to estimate possible base sliding of concrete gravity
dams induced by an earthquake is proposed. A simple mechanical model is developed to take
into account the most relevant parameters influencing seismic response such as dam-water and
dam-foundation interaction. In order to catch base residual displacement, a threshold value for
the sliding foundation resistance is fixed. The dam is modelled as an elastic linear single degree
of freedom system. The hydrodynamic effects of the water in the reservoir are taken into account
with generalized supplementary mass and force as well as by adding supplementary damping.
The foundation resistance is modelled with the Mohr-Coulomb criterion including a frictional
and a cohesive component and the presence of a passive wedge resistance is also considered.
A comprehensive numerical analysis of the response of concrete gravity dams subjected to several
natural earthquake records relative to events mainly happened in Italy is carried out to
estimate base residual displacement. Different parameters are considered such as dam height,
foundation rock parameters, water level, seismic intensity. As a result a simplified methodology
is developed to evaluate base residual displacement, once known dam geometry, response spectrum
of the seismic input, and the soil characteristics. The procedure permits to assess seismic
safety of the dam with respect to base sliding, as well as water level reduction necessary to
render the dam safe enough
Equipment isolation systems by means of semi active control devices
No full textIn this paper the isolation of a single equipment by means of a semi active control device item is investigated. The configuration of ground-mounted equipment, that is an equipment directly mounted on the ground, is studied, and a single horizontal component of ground acceleration is assumed as base excitation, having considered the sliding response of the equipment among the possible response modes. A numerical study on a single-DOF structural model equipped with a continuously variable elastic device subjected to harmonic input is discussed. The proposed control algorithm is based on semi active continuous control. The performances of the isolated equipment are compared with those of the corresponding case having assumed the semi active device operating in ON-OFF mode and conventional passive control, in order to investigate the applicability of a semi active continuous control law for the reduction of the dynamic response of structural base-excited systems
Seismic safety against base sliding of concrete gravity dams
No full textSeismic safety against base sliding of Italian concrete gravity dams subjected to strong earthquakes is reached by
means of a simplified procedure. The mechanical model is represented by a single degree of freedom system
having dynamical characteristics which take into account dam-water-foundation interaction. To catch plastic
displacement the non linearity of the substructure is modelled, having fixed a threshold value for the sliding
foundation resistance presented with the Mohr-Coulomb yielding criterion including a frictional and a cohesive
component. The positive effect of a passive wedge resistance is also included. Non linear dynamic response to
several natural earthquakes is evaluated for typical examples of Italian concrete gravity dams, considering the
effect of different foundation rocks. On the basis of the obtained results a simplified procedure to have a first
estimate of the base sliding without performing non linear analysis is proposed
Vibration Analysis and Models of Adjacent Structures Controlled by Magnetorheological Dampers
No full textThis paper deals with the vibration analysis of adjacent structures controlled by a magnetorheological (MR) damper and with the discussion of a numerical procedure for identification and definition of a reliable finite element model. The paper describes an extensive experimental campaign investigating the dynamic response, through shaking table tests, of a tridimensional four-story structure and a two-story structure connected by an MR device. Several base excitations and intensity levels are considered. The structures were tested in nonconnected and connected configuration, with the MR damper operating in passive or semiactive mode. Moreover, the paper illustrates a procedure for the structural identification and the definition of a reliable numerical model valid for adjacent structures connected by MR dampers. The procedure is applied in the original nonconnected configuration, which represents a linear system, and then in the connected configuration, which represents a nonlinear system due to the MR damper. In the end, the updated finite element model is reliable and suitable for all the considered configurations and the mass, damping, and stiffness matrices are derived. The experimental and numerical responses are compared and the results confirm the effectiveness of the identification procedure and the validation of the finite element model
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