1,720,988 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
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
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
Considerations on the optimal design of semi active magnetorheological dampers
No full textIn this paper the optimal semi active control of a system subjected to seismic input is studied. The control algorithm, working in ON-OFF mode, is based on the instantaneous optimal control theory. By taking advantage of this theory, an innovative methodology to obtain global optimal control, that is optimality along the whole seismic event, is proposed in order to surpass the disadvantage of instantaneous control which reaches local optimality only. The control device is a magnetorheological damper, modelled as a Bouc-Wen element in parallel at a viscous element. The variable parameter to be optimized is the input voltage. The time lag of the device is modeled as well. The procedure proposed is applied to a case study representing a four story structure controlled by a semi active bracing which uses a magnetorheological damper. Analyses with several seismic inputs, representing both cases of near and far field earthquakes, are carried out and results obtained with optimal control along the whole seismic event are compared with instantaneous optimal control
Optimal passive control of adjacent structures interconnected with non-linear hysteretic devices
No full textIn this paper, the optimal passive control of adjacent structures interconnected by nonlinear hysteretic devices is studied. For nonlinear devices the versatile Bouc–Wen model is adopted, whereas for seismic excitation a Gaussian zero mean white noise and a filtered white noise are used. To solve nonlinear equations of motion a simplified solution is carried out using a stochastic linearization technique. The problem of the optimal design of the devices is studied and solved in the case of a simple two-degrees-of-freedom model. In the optimization problem, an energy criterion associated with the concept of optimal performance of the hysteretic connection is used. The energy performance index is defined as a measure of the ratio between the energy dissipated in the device and the seismic input energy on the structure. Only two parameters are considered in the optimization problem of the device yielding force and elastic stiffness. The rigid and elastic plastic models for the device are studied and compared. The design procedure leads to very simple indications on the optimal values of the device's mechanical parameters; these optimal values substantially depend only on the mass and stiffness ratio between the two structures. Finally, some concise results about the effectiveness of the hysteretic connection for the seismic response mitigation of coupled structures are also given
A reduced order model for optimal design of 2-mdof adjacent structures connected by hysteretic dampers
No full textCoupling adjacent structures with supplemental control devices appears to be a useful method to mitigate structural response. In this work, a reduced order model for optimal design of two multi-degree-of-freedom (2-mdof) structures connected by hysteretic dampers is studied. The seismic input is modeled as a Gaussian white-noise stationary stochastic process. Since the passive connection is modeled as a nonlinear hysteretic element, represented by the differential Boue-Wen law, a stochastic linearization technique is applied in order to simplify the problem. The design procedure is based on replacing the 2-mdof system, with a generalized two single-degree-of-freedom (2-sdof) system, by using the principle of virtual displacements; here, each structure is represented by an elementary oscillator interconnected by a hysteretic device. Once the equivalent structural parameters of the generalized 2-sdof system is known, it is possible to carry out the optimal design of the connection by using simple spectra obtained by the authors in a previous work, where the optimal design of a horizontal hysteretic link connecting a 2-sdof system has been studied and solved. Illustrative examples confirm the entire methodology and also verify the effectiveness of hysteretic connection on seismic response. (c) 2007 Elsevier Ltd. All rights reserved
Investigation on the optimal properties of semi active control devices with continuous control for equipment isolation
No full textThe paper treats the semi active isolation of a single equipment, acceleration sensitive, by means of a variable elastic control device. A numerical study on a single degree of freedom (SDOF) structural model equipped with a continuously variable elastic device subjected to harmonic input is presented. The utilized control algorithm is derived by the Lyapunov method and specialized in order to obtain instantaneous optimality. In order to minimize the dynamic response of interest, i.e. the equipment absolute acceleration, some parameters that define the algorithm and the device are conveniently selected. The purpose of the paper is to investigate the optimal isolation properties of semi active variable stiffness devices with continuous control across the whole frequency spectrum. The performances of the isolated equipment are evaluated in terms of absolute acceleration transmissibility. Semi active continuous control is compared with semi active ON-OFF mode and conventional linear passive control. Results show that it is possible to choose conveniently the parameters regulating semi active continuous control in order to limit the absolute acceleration transmissibility at all the frequencies. In literature from problems concerning vibration isolation, transmissibility is alternatively defined in terms of absolute acceleration or displacement. Here, absolute displacement transmissibility is also estimated. It is observed that in case of semi active control, there are differences between the two transmissibility representations, and they do not lead to analogous results for evaluating the performance of the control system
Sperimentazione Dinamica su Tavola Vibrante di Strutture Controllate mediante Dispositivi Magnetoreologici
No full textNella presente memoria si riportano i risultati di una campagna sperimentale svolta su tavola vibrante presso il Centro di Ricerca ENEA, Casaccia, su due strutture adiacenti collegate da dispositivi semi attivi magnetoreologici. Il modello fisico, in scala 1:5, è costituito da due telai rispettivamente di 4 e 2 livelli, in acciaio, opportunamente controventati nella direzione ortogonale al moto sismico imposto. Il dispositivo magnetoreologico utilizzato, prodotto dalla Lord Corporation, ha una forza massima nominale di 4448 N, in corrispondenza di una corrente continua di input di 1 A, pari ad un voltaggio di 2.5 V. Esso può lavorare in modalità passiva, ovvero assegnando livelli di tensione costanti, o in modalità semi attiva, ovvero assegnando livelli di tensione variabili nel tempo, regolati attraverso un prescelto algoritmo di controllo. Il collegamento tra le due strutture è realizzato al secondo livello, dove sono attesi i maggiori spostamenti relativi, in modo da attivare significativamente anche le capacità dissipative dello smorzatore. L’algoritmo di controllo utilizzato è di tipo ON-OFF e discende dalla teoria del controllo ottimo istantaneo; esso si basa sulla minimizzazione istantanea di un opportuno indice di prestazione. Lo scopo della campagna sperimentale svolta è quello di verificare l’efficacia del controllo di strutture adiacenti sottoposte ad eccitazione sismica alla base, mediante dispositivi magnetoreologici. Al riguardo l’intera sperimentazione ha approfondito i seguenti aspetti: l'implementazione del sistema di controllo ed in particolare dell'algoritmo semi attivo utilizzato, la selezione del voltaggio di input ottimo, il confronto con altre strategie di controllo, l'influenza del tipo di input sismico, gli obiettivi di protezione selettiva e globale. I risultati ottenuti mostrano l’efficacia di tale tecnologia di controllo per la riduzione della risposta sismica di strutture adiacenti
Dimensionamento ottimale di dispositivi isteretici a collegamento di strutture adiacenti sottoposte ad eccitazione alla base.
No full textCaratterizzazione di un dispositivo magnetoreologico mediante prove sperimentali
No full textThe paper approaches the problem of structural control by means of the semi active technology. The experimentation is on a prototype magnetorheological (MR) device, produced by Lord Corporation. Both passive and semi active tests are conducted on the MR damper applying respectively different constant voltage levels and variable voltage levels, by using an optimal control algorithm, to define damper’s mechanical characteristics. An identification is then conducted focusing attention on two models, known from literature: Bingham model and modified Bouc-Wen model. Moreover an estimate of electrical delays for the MR damper is carried out
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