External timber-based low-damage exoskeletons for enhanced structural safety and energy efficiency.

The European building stock, mostly built post-World War II with no regard to seismic design and energy efficiency principles, is unsurprisingly facing significant safety and energy efficiency challenges. The structural/seismic vulnerability of existing buildings has been further confirmed by recent earthquake disasters (e.g., L’Aquila 2009, Emilia 2012, Centre Italy 2016, Turkey & Syria 2023), whereas the energy inefficiency is underscored by high energy consumption rates. An unprecedented effort is therefore required to achieve energy savings and decarbonization targets by 2030 and 2050, respectively, to meet the ambitious goals of the European Green Deal. Although several technical solutions are available for improving the energy efficiency, it is advantageous to pursue integrated renovation strategies (i.e., structural and energy efficient), especially when dealing with buildings located in zones with moderate-to-high seismicity. This work explores the application of exoskeleton-type solutions for integrated building renovation. Specifically, external load bearing systems consisting of low-damage timber-based structural members (i.e., Pres-Lam technology), that upgrade the seismic performance by working in parallel with the existing building. Such solution is attractive, given the potential to execute the intervention entirely from outside the building, limiting occupant disruption and avoiding decanting of inhabitants. This aspect is crucial in motivating owners to choose a combined renovation, rather than just focusing on the energy one. If the system is structurally unsafe, even low-to-moderate earthquakes can easily damage it, making the energy improvements ineffective. Concurrently, the exoskeleton operates as the support for a high-multi-performance “double-skin” facade system, contributing to enhanced energy efficiency and facilitating a holistic renovation. The main goal of this work is to prove the effectiveness of the proposed integrated renovation strategy through an illustrative case study. The overall performance of both the as-built and the retrofitted structures is assessed by means of seismic and dynamic energy analyses. Building on such results, a loss assessment procedure is implemented to quantify the overall socio/economic/environmental impact in the building lifespan. The findings provide evidence of the efficiency of the proposed strategy to enhance the seismic resilience and the environmental sustainability of the solution.