Design guidelines for precast structures with cladding panels

The current design practice of precast buildings is based on a frame mode, where the peripheral cladding panelsenter only as masses without anystiffness. The panels are then connected to the structure with fastenings dimensioned with a local calculation on the basis 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 (Italy) in 2009, Grenada (Spain) in 2010, and Emilia (Italy) in 2012. 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 were urgently required. The research project SAFECLADDING was thus aimed at investigating, by means of a balanced combination of experimental and analytical activity, the seismic behaviour of precast structures with cladding wall panels and at developing 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. The final outcome of the SAFECLADDING project is represented by a set of documents providing the design guidelines produced by the consortium. The guidelines have a theoretical derivation supported by the experimental results of the testing campaigns and numerical simulations performed within the project. General know-how on production practice and international literature on the subject have been also considered. The present document provides the design guidelines for precast structures with cladding panels. A companion document provides the design guidelines for the wall panel connections.