Design procedure for orthogonal steel exoskeleton structures for seismic strengthening

The steel exoskeleton systems are widespread structures applied on the external perimeter of an existing building designed to absorb the horizontal actions providing at the same time useful support for energy efficiency upgrading and architectural restyling. The growing interest in the use of exoskeletons is due to the possibility of creating an integrated retrofit (structural, energetic, formal and functional), combining “structural safety” with the concepts of “deep renovation”. Among many solutions present in the literature, in the present work, the steel exoskeletons placed orthogonally to the facade of the existing building have been analysed; this structural typology has the advantage to allow rapid retrofit execution without interfering with the activities carried out within the existing structure. In this framework, the aim of the present work is the introduction of a detailed step-by-step design procedure for steel exoskeletons systems adopted for seismic retrofit of existing buildings looking also at the accessibility and operability aspects. Each step of the procedure was individually explained and it was applied for the design of a strengthening intervention on a real single-storey steel industrial building. The existing building is located in Nusco (Av, Italy) which is classified as in medium–high seismic intensity area which corresponds a peak ground acceleration (ag) equal to 0.238 g. Non-linear analyses were conducted to assess the existing structure’s performance as well as to verify the effectiveness of the strengthening solutions designed. The use of the exoskeleton systems allows to strongly increase both the elastic stiffness and the resistance of the investigated industrial building without interrupting its product activity.