The growing international demand for energy efficiency has paved the way for new attempts in the architectural field, moving towards significant improvements in sustainable building design. The desire to reduce the energy consumption is closely related to the spread of Nearly-Zero Energy Buildings (NZEB) capable of coupling the aesthetic and functional features with energetic aspects to minimize building consumptions. Among the latest generation strategies that have made it possible to achieve this appealing target, façade systems play a fundamental role for the entire building system, not only from an aesthetic point of view but above all in terms of energy saving. Since the nineteenth century, the façade industry has evolved rapidly, leading to the transition from the load-bearing masonry wall to the external self-supporting envelope (the so-called "curtain wall") and, subsequently, to the shift of climate-energy functions from inside to outside, from which the Double Skin Façade (DSF) system was born. Recently, the concept to let DSF be movable with respect to the structure in order to improve the dynamical response of buildings has been proposed by Moon. While, in the past, the idea to let the cladding surfaces to undergo potentially large displacements, was hindered by the difficulty to realize suitable connections, due to the renewed interaction between technology and architecture, the possibility to realize movable and adaptive façades could nowadays be considered technically feasible. All the above mentioned facts provide the main motivation for the work described in this thesis, which aims to investigate advantages and disadvantages of the use of Movable Façades (MF) for vibration reduction of buildings. After a critical analysis of the state of the art, in the first part of the work, the performances of buildings equipped with MF are compared to those of analogous structures equipped with standard Tuned Mass Damper (TMD). As compared to classic TMDs, MFs offer an important advantage stemming from the fact that they use mass already available in the building, without wasting useful indoor space. The analyses show that, despite the strong similarities in the resulting equation of motions, the two systems may exhibit quite different responses and a critical analysis of the differences between the two systems is provided. The comparison shows that, depending on the mass and stiffness ratios, MFs can be potentially very efficient in reducing vibrations of the main structure, reaching levels of efficiency even larger than those obtainable by TMDs. However, the same study also shows that high efficiency of the MF can be obtained only at the price of displacements of the façade so large to significantly exceed functionally admissible levels. The main outcome of the first part of the work is that the limitation of the façade displacements is the paramount issue to be solved to let any application of MF feasible. Accordingly, the rest of the thesis is devoted to propose solutions aimed to solve this problem. In the second part of the thesis, a new connection device for MF is proposed. The device combines two main functional principles: a friction slider, inspired by the Variable Friction Cladding Connection (VFCC) device proposed by Laflamme and coworkers, and a system of dissipative bumper dampers, inspired by solutions adopted in the field of seismic pounding. The conception of the device and its nonlinear modeling are addressed in order to identify the main design parameters that influence the performances of the connection. In the third part of the thesis, the performances of MF connected to the building by simple friction sliders without bumpers are subject to a preliminary evaluation, based on a simplified two degrees-of-freedom (2DOF) model of a mid-rise RC frame building under harmonic excitation. This study shows that, although the presence of large friction dissipation can be, in some conditions, beneficial, large displacements of the façade remain an issue, hence strongly confirming the need of a complete devices equipped with bumpers. The performances of the complete device are then studied by means of parametric nonlinear dynamic analyses aimed to investigate the influence of the main design parameters. The main outcome of this part is that bumpers may be very efficient in reducing the façade displacements while keeping dynamical efficiency. However, it also turns out that the balance between the vibration reduction efficiency and façade displacement control may be delicate, as quite different results can be obtained depending on the frequency of the excitation. This result pointed out the need to re-evaluate the performances of MF under the more realistic situation of a building subject to wind actions, where the combination of several frequencies may give different results with respect to single-harmonic forcing. In the fourth part of the thesis, a multi degrees-of-freedom (MDOF) model of the same building considered in the third one, under the action of wind excitation is developed and used to investigate the performances of the MF connected to the structure by the complete device proposed in the second part. The analyses show that the use of connection devices with larger gaps with respect to bumpers provide better performances in terms of structure displacement although in some conditions acceleration performances may be reduced by impacts with bumpers. In the last part of the thesis, the case of the Isozaki tower, a 51-floors, 220-meters tall building recently realized in Milan (Italy) is studied. To mitigate wind-induced vibrations, Isozaki tower has been equipped with large viscoelastic dampers installed on the top of inclined trusses anchored to the façade and to the ground, externally to the building. Since such trusses have a strong impact in the visual appearance of the building, this case is a prominent example of interaction between structural and architectural aspects. The idea has been to redesign the façade of the tower in such a way to let 8 cladding blocks to rigidly move, relatively to the structure. A MDOF nonlinear model of the Isozaki tower with a multi-block MF has been realized and the performances of the building under the action of wind has been evaluated. The analyses show that, after a proper calibration of the various design parameters, the MF could achieve the desired serviceability performance levels both in terms of accelerations and displacements, without impacting in a significant way the architecture of the building. In conclusion, although real applications of MF are still to come, this thesis addressed some of the main conceptual issues to be solved. Of course, several other problems remain to be solved, especially at the technological level, but the preliminary results obtained here, seem to confirm that the idea initially advanced by Moon could become applicable.
La crescente domanda internazionale di efficienza energetica ha aperto la strada a nuovi tentativi in campo architettonico, orientandosi verso significativi miglioramenti nella progettazione dell’edilizia sostenibile. La volontà di ridurre i consumi energetici è strettamente correlata alla diffusione di Edifici a Energia Quasi Zero (EEQZ) in grado di coniugare le caratteristiche estetiche e funzionali con gli aspetti energetici per ridurre al minimo i consumi degli edifici. Tra le strategie di ultima generazione che hanno permesso di raggiungere questo traguardo, i sistemi di facciata giocano un ruolo fondamentale per l’intero sistema edilizio, non solo dal punto di vista estetico ma soprattutto in termini di risparmio energetico. A partire dal XIX secolo l’industria delle facciate si è evoluta rapidamente, portando al passaggio dalla parete portante in muratura all’involucro esterno autoportante (la cosiddetta "facciata continua") e, successivamente, allo spostamento delle funzioni climatico-energetiche dall’interno verso l’esterno degli edifici, da cui è nata la facciata a doppia pelle. Recentemente, Moon ha proposto l’idea di rendere mobile la facciata a doppia pelle rispetto alla struttura per migliorare la risposta dinamica degli edifici. Se in passato l’idea di far subire alle superfici di rivestimento spostamenti potenzialmente importanti rispetto alla struttura era ostacolata dalla difficoltà di realizzare opportuni collegamenti, grazie alla rinnovata interazione tra tecnologia e architettura, la possibilità di realizzare Facciate Mobili (FM) e adattabili potrebbe oggi essere considerata tecnicamente fattibile. Tutti i fatti sopra citati forniscono la motivazione principale per lo sviluppo del lavoro descritto in questa Tesi, che mira ad indagare vantaggi e svantaggi dell’uso delle FM per la riduzione delle vibrazioni degli edifici. Dopo un’analisi critica dello stato dell’arte, nella prima parte del lavoro, le prestazioni di edifici dotati di FM vengono confrontate con quelle di analoghe strutture dotate di smorzatori a massa accordata tradizionali, meglio noti come TMD. Rispetto ai classici TMD, le FM offrono un importante vantaggio derivante dal fatto che utilizzano massa già disponibile all’esterno dell’edificio, senza sprecare spazio utile interno. Le analisi mostrano che, nonostante le somiglianze nell’equazione del moto risultante, i due sistemi possono mostrare risposte abbastanza diverse, pertanto, viene fornita un’analisi critica delle differenze tra i due sistemi. Il confronto mostra che, a seconda dei rapporti di massa e rigidezza, le FM possono essere potenzialmente molto efficienti nel ridurre le vibrazioni della struttura principale, raggiungendo livelli di efficienza anche maggiori di quelli ottenibili dai TMD; tuttavia l’elevata efficienza delle FM può essere ottenuta solo al prezzo di spostamenti di facciata così grandi da superare i livelli funzionalmente ammissibili. Il principale risultato della prima parte del lavoro è che la limitazione degli spostamenti di facciata è la questione fondamentale da risolvere per rendere fattibile qualsiasi applicazione delle FM. Nella seconda parte della Tesi viene proposto un nuovo dispositivo di connessione per FM. Il dispositivo combina due principi funzionali principali: un cursore ad attrito ispirato ad un dispositivo di connessione ad attrito variabile proposto da Laflamme e suoi collaboratori, e un sistema di ammortizzatori dissipativi in gomma, ispirato alle soluzioni adottate nel campo del martellamento sismico. La concezione del dispositivo e la sua modellazione non lineare sono affrontate al fine di identificare i principali parametri progettuali che influenzano le prestazioni della connessione. Nella terza parte della Tesi, le prestazioni delle FM collegate all’edificio da semplici cursori ad attrito senza paraurti sono oggetto di una valutazione preliminare, basata su un modello semplificato a 2 gradi di libertà (GDL) di un edificio medio-alto in c.a. sotto eccitazione armonica. Questo studio mostra che, sebbene la presenza di una grande dissipazione per attrito possa essere, in alcune condizioni, benefica, i grandi spostamenti di facciata rimangono un problema, confermando quindi con forza la necessità di ricorrere a dispositivi completi dotati di paraurti. Le prestazioni del dispositivo completo vengono quindi studiate mediante analisi dinamiche parametriche non lineari volte ad indagare l’influenza dei principali parametri di progetto. Il risultato principale di questa parte è che i paraurti possono essere molto efficienti nel ridurre gli spostamenti di facciata mantenendo l’efficienza dinamica. Tuttavia, risulta anche che l’equilibrio tra l’efficienza di riduzione delle vibrazioni e il controllo degli spostamenti di FM può essere delicato, poiché si possono ottenere risultati molto diversi al variare della frequenza di eccitazione. Questo risultato ha messo in evidenza la necessità di rivalutare le prestazioni delle FM in uno scenario più realistico di edifici soggetti all’azione del vento, poichè la combinazione di più frequenze può fornire risultati diversi rispetto al forza prodotta da una singola armonica. Nella quarta parte della Tesi viene sviluppato un modello a più-GDL dello stesso edificio considerato nella terza fase, sotto l’azione dell’eccitazione del vento, utilizzato per indagare le prestazioni di FM collegata alla struttura con il dispositivo completo. Le analisi mostrano che l’uso di dispositivi di connessione con gap maggiori rispetto ai paraurti fornisce prestazioni migliori in termini di spostamento strutturale anche se, in alcune condizioni, le prestazioni di accelerazione possono essere ridotte dai contatti con i paraurti. Nell’ultima parte della Tesi viene studiato il caso della torre Isozaki, un edificio di 51 piani alto 220 metri recentemente realizzato a Milano (Italia). Per mitigare le vibrazioni indotte dal vento, la torre Isozaki è stata dotata di quattro coppie di dissipatori viscosi installati alla base di puntoni inclinati ancorati alla facciata, esternamente all’edificio. Poiché tali puntoni hanno un forte impatto sull’aspetto visivo dell’edificio, questo caso è un esempio lampante di interazione tra aspetti strutturali e architettonici. L’idea è stata quella di ridisegnare la facciata della torre in modo tale che gli otto blocchi di rivestimento si muovano rigidamente rispetto alla struttura. È stato realizzato un modello non lineare a più-GDL della torre Isozaki con una FM multiblocco e sono state valutate le prestazioni dell’edificio sotto l’azione del vento. Le analisi mostrano che, dopo un’opportuna calibrazione dei vari parametri progettuali, la FM potrebbe raggiungere i livelli prestazionali desiderati sia in termini di accelerazione che di spostamento, senza incidere in modo significativo sull’architettura dell’edificio. In conclusione, sebbene debbano ancora arrivare applicazioni reali di FM, questa Tesi ha affrontato alcuni dei principali problemi concettuali da risolvere. Naturalmente restano da risolvere altri problemi soprattutto a livello tecnologico, ma i risultati preliminari qui ottenuti sembrano confermare che l’idea inizialmente avanzata da Moon potrebbe diventare applicabile.
Movable façades for vibration reduction of buildings / DI GIOVANNI, Giulia. - (2022 May 23).
Movable façades for vibration reduction of buildings
DI GIOVANNI, GIULIA
23/05/2022
Abstract
The growing international demand for energy efficiency has paved the way for new attempts in the architectural field, moving towards significant improvements in sustainable building design. The desire to reduce the energy consumption is closely related to the spread of Nearly-Zero Energy Buildings (NZEB) capable of coupling the aesthetic and functional features with energetic aspects to minimize building consumptions. Among the latest generation strategies that have made it possible to achieve this appealing target, façade systems play a fundamental role for the entire building system, not only from an aesthetic point of view but above all in terms of energy saving. Since the nineteenth century, the façade industry has evolved rapidly, leading to the transition from the load-bearing masonry wall to the external self-supporting envelope (the so-called "curtain wall") and, subsequently, to the shift of climate-energy functions from inside to outside, from which the Double Skin Façade (DSF) system was born. Recently, the concept to let DSF be movable with respect to the structure in order to improve the dynamical response of buildings has been proposed by Moon. While, in the past, the idea to let the cladding surfaces to undergo potentially large displacements, was hindered by the difficulty to realize suitable connections, due to the renewed interaction between technology and architecture, the possibility to realize movable and adaptive façades could nowadays be considered technically feasible. All the above mentioned facts provide the main motivation for the work described in this thesis, which aims to investigate advantages and disadvantages of the use of Movable Façades (MF) for vibration reduction of buildings. After a critical analysis of the state of the art, in the first part of the work, the performances of buildings equipped with MF are compared to those of analogous structures equipped with standard Tuned Mass Damper (TMD). As compared to classic TMDs, MFs offer an important advantage stemming from the fact that they use mass already available in the building, without wasting useful indoor space. The analyses show that, despite the strong similarities in the resulting equation of motions, the two systems may exhibit quite different responses and a critical analysis of the differences between the two systems is provided. The comparison shows that, depending on the mass and stiffness ratios, MFs can be potentially very efficient in reducing vibrations of the main structure, reaching levels of efficiency even larger than those obtainable by TMDs. However, the same study also shows that high efficiency of the MF can be obtained only at the price of displacements of the façade so large to significantly exceed functionally admissible levels. The main outcome of the first part of the work is that the limitation of the façade displacements is the paramount issue to be solved to let any application of MF feasible. Accordingly, the rest of the thesis is devoted to propose solutions aimed to solve this problem. In the second part of the thesis, a new connection device for MF is proposed. The device combines two main functional principles: a friction slider, inspired by the Variable Friction Cladding Connection (VFCC) device proposed by Laflamme and coworkers, and a system of dissipative bumper dampers, inspired by solutions adopted in the field of seismic pounding. The conception of the device and its nonlinear modeling are addressed in order to identify the main design parameters that influence the performances of the connection. In the third part of the thesis, the performances of MF connected to the building by simple friction sliders without bumpers are subject to a preliminary evaluation, based on a simplified two degrees-of-freedom (2DOF) model of a mid-rise RC frame building under harmonic excitation. This study shows that, although the presence of large friction dissipation can be, in some conditions, beneficial, large displacements of the façade remain an issue, hence strongly confirming the need of a complete devices equipped with bumpers. The performances of the complete device are then studied by means of parametric nonlinear dynamic analyses aimed to investigate the influence of the main design parameters. The main outcome of this part is that bumpers may be very efficient in reducing the façade displacements while keeping dynamical efficiency. However, it also turns out that the balance between the vibration reduction efficiency and façade displacement control may be delicate, as quite different results can be obtained depending on the frequency of the excitation. This result pointed out the need to re-evaluate the performances of MF under the more realistic situation of a building subject to wind actions, where the combination of several frequencies may give different results with respect to single-harmonic forcing. In the fourth part of the thesis, a multi degrees-of-freedom (MDOF) model of the same building considered in the third one, under the action of wind excitation is developed and used to investigate the performances of the MF connected to the structure by the complete device proposed in the second part. The analyses show that the use of connection devices with larger gaps with respect to bumpers provide better performances in terms of structure displacement although in some conditions acceleration performances may be reduced by impacts with bumpers. In the last part of the thesis, the case of the Isozaki tower, a 51-floors, 220-meters tall building recently realized in Milan (Italy) is studied. To mitigate wind-induced vibrations, Isozaki tower has been equipped with large viscoelastic dampers installed on the top of inclined trusses anchored to the façade and to the ground, externally to the building. Since such trusses have a strong impact in the visual appearance of the building, this case is a prominent example of interaction between structural and architectural aspects. The idea has been to redesign the façade of the tower in such a way to let 8 cladding blocks to rigidly move, relatively to the structure. A MDOF nonlinear model of the Isozaki tower with a multi-block MF has been realized and the performances of the building under the action of wind has been evaluated. The analyses show that, after a proper calibration of the various design parameters, the MF could achieve the desired serviceability performance levels both in terms of accelerations and displacements, without impacting in a significant way the architecture of the building. In conclusion, although real applications of MF are still to come, this thesis addressed some of the main conceptual issues to be solved. Of course, several other problems remain to be solved, especially at the technological level, but the preliminary results obtained here, seem to confirm that the idea initially advanced by Moon could become applicable.File | Dimensione | Formato | |
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