Since its conception in the mid 90’s, cross-laminated timber, known also as CLT or X-Lam, has achieved a great popularity as construction material thanks to its numerous intrinsic qualities, worldwide effort to build reliable structures in seismic-prone areas and necessity to build a more eco-friendly environment. Many tests have been carried out in the last 15 years, aimed to better understand the behavior of connections in CLT buildings, CLT assemblies and CLT structures in order to provide reliable rules for designers to design structures made of CLT in any loading condition. Based on these tests, many numerical models have been suggested through the years. They represent a fundamental tool for the design of CLT structures when specific design problems arise. Despite many years of efforts, reliable design rules are still missing in almost every code worldwide and many are still the unknown related to CLT structures behavior at many levels (connections, assemblies, structures). This thesis summarizes three years of numerical investigations, which have faced different problems related to the comprehension of CLT assemblies and structures behavior under dynamic loading conditions. The first part of this path focused on the continuation of a previous study made within the Master Degree thesis, which was the formulation of a simplified method to obtain an axial-load/bending moment limit domain for a CLT panel connected to the supporting surface through hold-down and angle bracket connections. Without test results of interest, the focus of the study returned to be the formulation of simple methods for CLT assemblies design. The problem of panel-to-panel connections was investigated. In particular, the stiffness of such connections related to the rocking behavior of 2-panel wall assemblies was studied through full-scale tests and FE numerical analyses. A formula for the design of these connections was firstly suggested and then, after further analyses, revised and corrected. In order to extend the analyses and consider more complex assemblies, the influence of diaphragm and wall-to-diaphragm connections stiffness on the rocking behavior of wall assemblies was numerically investigated, taking into account configuration with and without diaphragm, varying several parameters to obtain statistically significant results. In the summer of 2017 the candidate actively participated to the NHERI TallWood Project, an American research project intended to test CLT structures in order to provide design rules for these structures in the future US codes. Sponsored by the Colorado State University, in the person of Professor John W. van de Lindt, the candidate collaborated to the setup of a 2-story CLT building that was tested on the UCSD shaking table located in San Diego (California). In order to assess the most proper value of damping for CLT structures under low-intensity seismic events and to better investigate the potential of the component approach for the modelling of CLT structures, the 0,15 g shaking table tests of the 3-story building within the SOFIE Project were reproduced and analyzed. Further considerations on the role of friction for this type of structure have been made together with the problem of linear analyses for CLT structures (non-symmetric response for tension-compression loaded connections).
Dalla sua concezione a metà degli anni novanta, il legno lamellare a strati incrociati, anche noto come CLT o X-Lam, ha raggiunto grande popolarità tra i materiali da costruzione grazie alle numerose innate qualità, gli sforzi a livello mondiale per costruire strutture affidabili in zone a rischio sismico e la necessità di costruire un ambiente più eco-sostenibile. Molti test sono stati fatti negli ultimi 15 anni, volti a comprendere meglio il comportamento delle connessioni in edifici in CLT, di parti strutturali o di intere strutture in CLT, in modo da fornire regole affidabili per i progettisti per progettare strutture in CLT sotto ogni condizione di carico. Sulla base di questi test, molti sono stati i modelli numerici che sono stati suggeriti negli anni. Questi rappresentano uno strumento fondamentale per la progettazione di strutture in CLT quando insorgono specifiche problematiche ed un approccio analitico da solo non è sufficiente. Nonostante i molti anni di sforzi, non esistono ancora affidabili metodologie di progetto nella quasi totalità dei codici a livello mondiale e ancora molte sono le incognite relative al comportamento delle strutture in CLT a molti livelli (connessioni, parti strutturali, strutture). Questa tesi riassume tre anni di ricerche numeriche, le quali hanno affrontato diversi problemi relativi al comportamento di elementi strutturali e strutture in CLT sotto azioni dinamiche. Durante la prima parte di questo percorso l’attenzione è stata posta sulla continuazione di un precedente studio, portato avanti durante la tesi di laurea magistrale, il quale era incentrato sulla formulazione di un metodo semplificato per la costruzione di un dominio resistente sforzo normale-momento flettente per pannelli in CLT connessi alla base da connessioni tipo hold-down e angle bracket. In mancanza di risultati di test di interesse, la concentrazione è stata rivolta ancora alla formulazione di metodi semplificati per la progettazione di elementi strutturali in CLT. È stato analizzato il problema delle connessioni pannello-pannello all’interno di una stessa parete. In particolare, è stata studiata la rigidezza di queste connessioni in relazione al comportamento ribaltante di pareti a due pannelli attraverso l’analisi di test a scala reale indipendenti e analisi numeriche agli elementi finiti. Una formula per il calcolo di queste connessioni è stata dapprima proposta e poi, dopo ulteriori analisi, rivista e corretta. Per estendere l’analisi e considerare elementi strutturali più complessi, è stata investigata, a livello di analisi numerica, l’influenza del solaio e delle connessioni parete-solaio superiore sul comportamento ribaltante delle pareti, prendendo in considerazione configurazioni con e senza solaio, variando diversi parametri di modo da ottenere risultati statisticamente significativi. Nell’estate del 2017 il candidato ha partecipato attivamente al NHERI TallWood Project, una ricerca statunitense intesa a testare strutture in CLT per fornire regole di progettazione per tali strutture nei futuri codici nazionali. Sponsorizzato dalla Colorado State University, nella persona del Prof. John W. van de Lindt, il candidato ha collaborato alla preparazione di un edificio con due orizzontamenti fuori terra testato sulla tavola vibrante della UCSD a San Diego (California) Per valutare il più corretto valore di smorzamento per strutture in CLT sotto l’azione di eventi sismici di bassa intensità, sono stati riprodotti numericamente ed analizzati i test su tavola vibrante del progetto SOFIE a 0,15 g. Ulteriori considerazioni sono state fatte sul ruolo dell’attrito su questo tipo di strutture e sul problema delle analisi lineari per strutture in CLT (risposta non simmetrica di connessioni caricate in tensione-compressione).
Numerical modelling and design methods for CLT structures / Tamagnone, Gabriele. - (2019 Mar 28).
Numerical modelling and design methods for CLT structures
TAMAGNONE, GABRIELE
2019-03-28
Abstract
Since its conception in the mid 90’s, cross-laminated timber, known also as CLT or X-Lam, has achieved a great popularity as construction material thanks to its numerous intrinsic qualities, worldwide effort to build reliable structures in seismic-prone areas and necessity to build a more eco-friendly environment. Many tests have been carried out in the last 15 years, aimed to better understand the behavior of connections in CLT buildings, CLT assemblies and CLT structures in order to provide reliable rules for designers to design structures made of CLT in any loading condition. Based on these tests, many numerical models have been suggested through the years. They represent a fundamental tool for the design of CLT structures when specific design problems arise. Despite many years of efforts, reliable design rules are still missing in almost every code worldwide and many are still the unknown related to CLT structures behavior at many levels (connections, assemblies, structures). This thesis summarizes three years of numerical investigations, which have faced different problems related to the comprehension of CLT assemblies and structures behavior under dynamic loading conditions. The first part of this path focused on the continuation of a previous study made within the Master Degree thesis, which was the formulation of a simplified method to obtain an axial-load/bending moment limit domain for a CLT panel connected to the supporting surface through hold-down and angle bracket connections. Without test results of interest, the focus of the study returned to be the formulation of simple methods for CLT assemblies design. The problem of panel-to-panel connections was investigated. In particular, the stiffness of such connections related to the rocking behavior of 2-panel wall assemblies was studied through full-scale tests and FE numerical analyses. A formula for the design of these connections was firstly suggested and then, after further analyses, revised and corrected. In order to extend the analyses and consider more complex assemblies, the influence of diaphragm and wall-to-diaphragm connections stiffness on the rocking behavior of wall assemblies was numerically investigated, taking into account configuration with and without diaphragm, varying several parameters to obtain statistically significant results. In the summer of 2017 the candidate actively participated to the NHERI TallWood Project, an American research project intended to test CLT structures in order to provide design rules for these structures in the future US codes. Sponsored by the Colorado State University, in the person of Professor John W. van de Lindt, the candidate collaborated to the setup of a 2-story CLT building that was tested on the UCSD shaking table located in San Diego (California). In order to assess the most proper value of damping for CLT structures under low-intensity seismic events and to better investigate the potential of the component approach for the modelling of CLT structures, the 0,15 g shaking table tests of the 3-story building within the SOFIE Project were reproduced and analyzed. Further considerations on the role of friction for this type of structure have been made together with the problem of linear analyses for CLT structures (non-symmetric response for tension-compression loaded connections).File | Dimensione | Formato | |
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