SAFECLADDING · IMPROVED FASTENING SYSTEMS OF CLADDING WALL PANELSOF PRECAST BUILDINGS IN SEISMIC ZONES

The current design practice of precast buildings is based on a frame model where the peripheral cladding panels enter only as masses without anystiffness. The panels are then connected to the structure with fastenings dimensioned with a local calculation on the base of their mass for anchorage forces orthogonal to the plane of the panels. This design approach does not work, as it was recently dramatically shown by several recent violent shakes, like L’Aquila in 2009 and Grenada in 2010. The panels, fixed in this way to the structure, come to be integral part of the resisting system conditioning its seismic response. The high stiffness of this resisting system leads to forces much higher than those calculated from the frame model. These forces are related to the global mass of the floors and are primarily directed in the plane of the walls. Furthermore, the seismic force reduction in the type of precast structures of concern relies on energy dissipation in plastic hinges formed in the columns. Very large drifts of the columns are needed to activate this energy dissipation foreseen in design. However, typically the capacity of the connections between cladding and structure is exhausted well before such large drifts can develop. Therefore, the design of these connections cannot rely on the seismic reduction factor used for design of the bare structure. New technological solutions for connectors with proper design approaches areurgently required. The research project SAFECLADDING is thus aimed to investigate, by means of a balanced combination of experimental andanalytical activity, the seismic behaviour of precast structures with cladding wall panels and to develop innovative connection devices and novel design approaches for a correct conception and dimensioning of the fastening system to guarantee good seismic performance of the structure throughout its service life.