The Emilia earthquake of May 20 and 29 2012 has once more proven that the most critical elements in industrial precast buildings are the connections. Most of the collapses and damages observed may be in fact ascribed to the failure of the connections, or to the lack of connections able to efficiently avoid the loss of support of precast elements. The observed vulnerabilities are mainly due to a design in which the possibility of a seismic event was not considered, being the area struck by the earthquake classified as seismic only since 2003, and being seismic design compulsory only starting from the end of 2004. Precast buildings erected before seismic design was mandatory were conceived to mainly resist gravity forces, with horizontal forces, generally small, due only to wind or to the crane movement. Under these conditions, friction connections, otherwise forbidden in seismic zones, were often adopted between roof elements and main girders, and between the latter and columns, while the lateral restraint of main beams, often made with end forks, was computed to resist small transverse actions, even if the beams were often characterized by large spans and considerable height. The connections between the external cladding panels and the main structure were made using vertical brackets and horizontal retention systems designed to resist the panel weight, and they were certainly not meant to resist a seismic action acting either in the panel plane or transversally to such a plane. Furthermore, such connections were not generally able to allow significant relative displacements between the structure and the panels, thus forcing the panels to act as bracing systems, until the connection failure would be reached. Such vulnerabilities have been recognised by the Law Decree 74 of June 6 2012, converted in Law 122 of August 1 2012, which imposes that in order to obtain the seismic fit for use certificate, the following vulnerabilities should be preliminarily removed in precast industrial buildings: a) lack of connections between vertical and horizontal elements and between the latter ones; b) existence of precast claddings not adequately connected to the main structures; c) existence of un-braced scaffoldings carrying heavy goods which could, during their collapse, affect the main structure causing its damage or collapse. Given the above, the Board of ACI Italy Chapter decided that it would have been of paramount interest to organize, at the University of Bergamo, a workshop on connections in precast structures which would bring together designers and researchers active on the subject. The papers presented at the workshop are published in these proceedings.

Il terremoto Emiliano del 20 e 29 maggio 2012 ha una volta di più dimostrato che l’elemento maggiormente critico negli edifici industriali prefabbricati è rappresentato dalle connessioni. Gran parte dei collassi e dei danni riscontrati in edifici prefabbricati durante il terremoto è infatti imputabile al collasso delle connessioni, oppure alla mancanza di collegamenti che possano efficacemente impedire la perdita di appoggio tra gli elementi prefabbricati. Le carenze riscontrate sono principalmente dovute ad una progettazione nella quale l’eventualità di un evento sismico è stata trascurata, essendo la zona colpita dal terremoto classificata come sismica solamente a partire dal 2003, ed essendo la progettazione sismica in tale zona obbligatoria solo dalla fine del 2004. Gli edifici prefabbricati realizzati prima della entrata in vigore dell’obbligo di progettazione sismica erano concepiti per resistere prevalentemente alle azioni verticali, con azioni orizzontali, generalmente di modesta entità, rappresentate solo dal vento o dalle azioni del carroponte. In tale contesto, tra gli elementi di copertura e le travi e tra quest’ultime ed i pilastri erano frequentemente realizzati vincoli ad attrito, esplicitamente vietati in zona sismica, ed il contenimento trasversale delle travi portanti, frequentemente realizzato con forcelle, era dimensionato per sostenere azioni trasversali di modesta entità, pur in presenza di travi di grande luce ed altezza. I collegamenti tra pannelli di facciata e le strutture prefabbricate era poi affidato ad appoggi e ritenute dimensionate per sopportare il solo peso dei pannelli prefabbricati, e non certamente per sopportare un’azione simica rilevante agente sia nel piano del pannello, sia nel piano ad esso ortogonale. Inoltre, tali collegamenti non erano generalmente in grado di consentire spostamenti significativi tra i pannelli e la struttura, facendo sì che i pannelli si comportassero da elementi di controvento, almeno fin tanto che le connessioni non giungevano a collasso. A riconoscimento di tali carenze, il DL 74 del 6 giugno 2012, poi convertito nella legge 122 del 1 agosto 2012, impone che per avere l’agibilità sismica definitiva negli edifici industriali prefabbricati debbano essere preliminarmente eliminate le seguenti carenze: a) mancanza di collegamenti tra elementi strutturali verticali e elementi strutturali orizzontali e tra questi ultimi; b) presenza di elementi di tamponatura prefabbricati non adeguatamente ancorati alle strutture principali; c) presenza di scaffalature non controventate portanti materiali pesanti che possano, nel loro collasso, coinvolgere la struttura principale causandone il danneggiamento e il collasso. In ragione di quanto sopra esposto, il Board di ACI Italy Chapter ha ritenuto di fondamentale interesse organizzare presso l’Università di Bergamo un workshop che portasse i tecnici ed i ricercatori che si occupano di collegamenti nelle strutture prefabbricate ad un confronto sul tema. Il presente volume raccoglie le memorie presentate durante tale Workshop.

Connections in Precast Concrete : I collegamenti nelle strutture prefabbricate, Workshop proceedings, 5 October 2012, University of Bergamo, Chiostro di Sant'Agostino

RIVA, Paolo;
2013-01-01

Abstract

The Emilia earthquake of May 20 and 29 2012 has once more proven that the most critical elements in industrial precast buildings are the connections. Most of the collapses and damages observed may be in fact ascribed to the failure of the connections, or to the lack of connections able to efficiently avoid the loss of support of precast elements. The observed vulnerabilities are mainly due to a design in which the possibility of a seismic event was not considered, being the area struck by the earthquake classified as seismic only since 2003, and being seismic design compulsory only starting from the end of 2004. Precast buildings erected before seismic design was mandatory were conceived to mainly resist gravity forces, with horizontal forces, generally small, due only to wind or to the crane movement. Under these conditions, friction connections, otherwise forbidden in seismic zones, were often adopted between roof elements and main girders, and between the latter and columns, while the lateral restraint of main beams, often made with end forks, was computed to resist small transverse actions, even if the beams were often characterized by large spans and considerable height. The connections between the external cladding panels and the main structure were made using vertical brackets and horizontal retention systems designed to resist the panel weight, and they were certainly not meant to resist a seismic action acting either in the panel plane or transversally to such a plane. Furthermore, such connections were not generally able to allow significant relative displacements between the structure and the panels, thus forcing the panels to act as bracing systems, until the connection failure would be reached. Such vulnerabilities have been recognised by the Law Decree 74 of June 6 2012, converted in Law 122 of August 1 2012, which imposes that in order to obtain the seismic fit for use certificate, the following vulnerabilities should be preliminarily removed in precast industrial buildings: a) lack of connections between vertical and horizontal elements and between the latter ones; b) existence of precast claddings not adequately connected to the main structures; c) existence of un-braced scaffoldings carrying heavy goods which could, during their collapse, affect the main structure causing its damage or collapse. Given the above, the Board of ACI Italy Chapter decided that it would have been of paramount interest to organize, at the University of Bergamo, a workshop on connections in precast structures which would bring together designers and researchers active on the subject. The papers presented at the workshop are published in these proceedings.
curatela (Atti di Convegno)
2013
Riva, Paolo; Realfonzo, Roberto
File allegato/i alla scheda:
Non ci sono file allegati a questa scheda.
Pubblicazioni consigliate

Aisberg ©2008 Servizi bibliotecari, Università degli studi di Bergamo | Terms of use/Condizioni di utilizzo

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10446/30140
Citazioni
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact