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Scotta, Roberto and Marchi, Luca and Trutalli, Davide and Pozza, Luca (2019) X-bracket. A high-ductility and dissipative connection for earthquake-resistant cross-laminated timber structures. [Technical Report]

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Abstract (italian or english)

Cross-laminated timber is a construction material with significant potential to realize multi-storey earthquake-resistant buildings, exploiting the lightness of timber and the high in-plane strength and stiffness of the shear-wall panels, conferred by cross lamination of massive boards. In such buildings, connections play a vital role to assure an optimal seismic performance. However, traditional connections, i.e., angle brackets and hold-downs, have well-known drawbacks: low dissipative capacity due cyclic deformation of fasteners with consequent wood embedment and possible brittle failures due to uncertainty of actual strength of fasteners and relative overstrength factors. The increasing diffusion of tall cross-laminated timber buildings in high-seismicity areas requires the development of new strategies to increase ductility and dissipative capacities and to improve the reliability of the ductile parts of the structure. Both these purposes can be achieved with the adoption of new connections with optimized cyclic behaviour and localization of deformation in a steel element, preventing damage to the timber panel. A new connection for cross-laminated timber structures named “X-bracket” has been designed and tested at the University of Padova; it works both in tension and shear and can be used as panel-to-panel or panel-to-foundation joint. The special “X” shape is optimized to assure high stiffness and diffused yielding of material, resulting in extraordinarily high ductility and dissipative capacities. Furthermore, the possibility of producing multiple elements from cutting of a mild steel plate with minimal waste of material assures low production costs. This Report presents main details of the X-bracket and summarizes the research activities from the initial design phase to the experimental validation, discussing results from numerical simulations and laboratory tests. Installation, anchoring to the panel and possibility of replacement after a strong earthquake are also addressed and supported by additional tests, to verify the reliable response and controlled overstrength of the X-bracket, in compliance with capacity design.

Abstract (a different language)

L’XLam è un materiale costruttivo con potenzialità significative nella realizzazione di edifici multipiano antisismici, sfruttando la leggerezza del legno e un’elevata rigidezza e resistenza nel piano del pannello, conferiti dalla laminazione a strati incrociati delle tavole in legno massiccio. In tali edifici, le connessioni giocano un ruolo fondamentale nell’assicurare una risposta sismica ottimale. Tuttavia, le connessioni tradizionali, conosciute come angolari e hold-down, presentano alcuni inconvenienti: bassa capacità dissipativa a causa della deformazione ciclica della chiodatura con conseguente perdita progressiva di efficacia a causa del rifollamento del legno; possibilità di rotture fragili a causa delle incertezze sulla reale resistenza della chiodatura e sui relativi fattori di sovraresistenza da utilizzare nella progettazione in capacità richiesta dalle attuali normative. La crescente diffusione di edifici alti in XLam in zone ad alto rischio sismico richiede lo sviluppo di nuove strategie per aumentare la duttilità e la capacità dissipativa e per migliorare l’affidabilità delle parti duttili della struttura. Questi due obiettivi possono essere raggiunti con l’utilizzo di nuove connessioni, aventi un comportamento ciclico ottimizzato, grazie alla localizzazione delle deformazioni in un elemento in acciaio al fine di prevenire il danneggiamento del pannello in legno. La staffa “X-bracket” è una connessione innovativa, progettata e testata all’Università di Padova. Tale connessione lavora sia a trazione che a taglio e può essere utilizzata come giunto tra due pannelli o tra pannello e fondazione. La speciale forma a “X” è ottimizzata per assicurare un’elevata rigidezza e una diffusione dello snervamento del materiale, ottenendo duttilità e capacità dissipative eccezionalmente alte. Inoltre, la possibilità di produrre molteplici elementi dal taglio di una piastra in acciaio, riducendo al minimo lo scarto di materiale, assicura un basso costo di produzione. Questo Report presenta i principali dettagli della staffa X-bracket e riassume le attività di ricerca condotte a partire dalla fase di progettazione fino alla validazione sperimentale, discutendo i risultati delle simulazioni numeriche e dei test in laboratorio. L’installazione, l’ancoraggio al pannello e la possibilità di sostituzione del dispositivo in seguito ad un evento sismico di elevata intensità sono discusse e supportate da test aggiuntivi, al fine di verificare l’affidabilità della risposta sismica e l’effettiva sovraresistenza da assumere nella progettazione in capacità.

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EPrint type:Technical Report
Anno di Pubblicazione:February 2019
Key Words:X-bracket; cross-laminated timber; CLT; XLam; timber structures; innovative connections; dissipative connections; ductile connections; capacity design; earthquake-resistant buildings; numerical simulations; experimental tests. X-bracket; cross-laminated timber; CLT; XLam; strutture in legno; connessioni innovative; connessioni dissipative; connessioni duttili; progettazione in capacità; edifici antisismici; simulazioni numeriche; test sperimentali.
Codice ID:11823
Depositato il:26 Feb 2019 16:13
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