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

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.