The need to overcome obstacles on very long distances typically implies the design of "streamlined" closed-box bridge decks. The size and lightness characterizing these structures make them very sensitive to dynamic problems and special care must be put in the design against the wind action. Dealing with this aspect, many difficulties are involved both in the wind description and in the computation of the bridge response, making the definition of good numerical codes a fundamental step. Nowadays, numerical models for the design of long-span bridges are mainly linearized models carried out both in frequency and time domain. However, some non-linear models can be found in the time domain. This models are, in fact, more appropriate to describe all the complex aspects related to the aerodynamic forces generated by the high fluctuations of the angle of attack. Unfortunately, such models are strongly limited by their applicability range since they would be more appropriate only to describe the non-linearities associated with the low frequency fluctuations of the incoming wind turbolence. An attempt to take into account also the non-linear contributions of the high frequencies is presented in this thesis where a new numerical approach based on the definition of rheological models has been developed and finally validated. Various simulations have been run to test the numerical procedure and comparisons were made with wind-tunnel tests. Code validation was done in a systematic way, starting from a simple linearized model and increasing the degree of complexity until the procedure was assessed robust enough to sustain the analysis of a full non-linear problem. The wind-tunnel tests were performed at Politecnico di Milano and were part of an international benchmark project conducted by the Politecnico di Milano and promoted by the International Association for Bridge and Structural Engineering (IABSE).
La necessità di sorpassare ostacoli su distanze molto lunghe favorisce la progettazione di ponti a cassone molto snelli. Le dimensioni e la leggerezza che caratterizzano queste strutture le rendono molto sensibili ai problemi dinamici e, in particolare, occorre prestare molta attenzione nella progettazione contro l’azione del vento turbolento. In tal senso, si riscontrano molte difficoltà sia nella descrizione del vento che nel calcolo della risposta del ponte, rendendo pertanto fondamentale la definizione di un buon codice numerico. Al giorno d'oggi, i modelli numerici connessi allo studio di ponti di grande luce sono per la maggior parte modelli linearizzati definiti sia nel dominio delle frequenze sia nel dominio del tempo. Si possono comunque trovare modelli non lineari definiti nel dominio del tempo. Questi modelli sono infatti necessari se si vogliono analizzare tutti gli aspetti complessi legati alle forze aerodinamiche generate dalle grandi fluttuazioni dell'angolo d'attacco. Tuttavia, questi metodi sono fortemente limitati dal dominio di applicabilità poiché adatti a descrivere le non linearità associate solamente alla variazione in bassa frequenza del vento turbolento. Un tentativo di estendere questo approccio anche alle non linearità legate alle alte frequenze è presentato in questo lavoro di tesi in cui un nuovo modello basato sulla definizione di modelli reologici è stato sviluppato ed infine validato. Varie simulazioni sono state condotte per testare il metodo numerico e confronti sono stati fatti con le prove sperimentali eseguite in galleria del vento. La validazione del modello è stata svolta in maniera sistematica, partendo da formulazioni semplici e aumentando il grado di complessità fino a quando la procedura è stata ritenuta sufficientemente robusta per l'analisi di un modello completamente non lineare. Le prove in galleria del vento sono state condotte presso il Politecnico di Milano e sono inserite all'interno di un benchmark internazionale condotto dal Politecnico di Milano e promosso dall'Associazione Internazionale di Ponti e Grandi Strutture (IABSE).
A time-domain approach based on rheological models for the buffeting response of long-span bridges
BRUSAMOLINO, ANDREA
2018/2019
Abstract
The need to overcome obstacles on very long distances typically implies the design of "streamlined" closed-box bridge decks. The size and lightness characterizing these structures make them very sensitive to dynamic problems and special care must be put in the design against the wind action. Dealing with this aspect, many difficulties are involved both in the wind description and in the computation of the bridge response, making the definition of good numerical codes a fundamental step. Nowadays, numerical models for the design of long-span bridges are mainly linearized models carried out both in frequency and time domain. However, some non-linear models can be found in the time domain. This models are, in fact, more appropriate to describe all the complex aspects related to the aerodynamic forces generated by the high fluctuations of the angle of attack. Unfortunately, such models are strongly limited by their applicability range since they would be more appropriate only to describe the non-linearities associated with the low frequency fluctuations of the incoming wind turbolence. An attempt to take into account also the non-linear contributions of the high frequencies is presented in this thesis where a new numerical approach based on the definition of rheological models has been developed and finally validated. Various simulations have been run to test the numerical procedure and comparisons were made with wind-tunnel tests. Code validation was done in a systematic way, starting from a simple linearized model and increasing the degree of complexity until the procedure was assessed robust enough to sustain the analysis of a full non-linear problem. The wind-tunnel tests were performed at Politecnico di Milano and were part of an international benchmark project conducted by the Politecnico di Milano and promoted by the International Association for Bridge and Structural Engineering (IABSE).File | Dimensione | Formato | |
---|---|---|---|
Tesi_AB.pdf
accessibile in internet per tutti
Descrizione: Testo della tesi
Dimensione
24.51 MB
Formato
Adobe PDF
|
24.51 MB | Adobe PDF | Visualizza/Apri |
I documenti in POLITesi sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/10589/152402