Integrated, sustainable, low-impact retrofitting through exoskeleton structures : a case study

Improvement of safety and eco-efficiency of existing buildings is an interdisciplinary problem: this is an established, although recent, research and policy acquisition. The age profile analysis of the EU's building heritage reveals that the main part of this 27 billion m^2 stock was built between 1961 and 1990, and a significant percentage before 1960. Poor thermal and environmental performances, as well as the failure to comply with modern seismic design codes, are common problems that require an integrated solution approach (Caverzan et al. 2016). In this context, exoskeleton structures appear to be a promising retrofitting strategy due to a number of reasons: the potential for a multifunctional design combining structural safety, energy efficiency and environmental sustainability; limited interference with existing structural and nonstructural components; minimal service or business downtime during the retrofitting process (Reggio et al. 2018). In this paper, a case study is presented, dealing with the integrated, seismic and energy, retrofitting of a mid-rise building, located in the city of Torino (Italy). The existing structure, a non-ductile reinforced concrete frame, is coupled via a rigid connection to an exoskeleton structure, realised as a steel braced frame. The exoskeleton structure is set adjacent to the existing structure and designed in order to reduce the seismic response of the latter, in terms of displacements and internal forces. In the perspective of an integrated design approach, the exoskeleton structure is further used to support external thermal insulation panels, aimed at the energy upgrading of the building envelope. Possible interference and synergies between seismic and energy retrofitting requirements are highlighted and discussed.