The latent threat of destructive earthquakes, in addition to the growing awareness of the need for environmentally sustainable housing, calls for an upgrade of the existing building stock to enhance both its structural safety and energy efficiency.

The high seismic risk of countries in the Mediterranean area  (e.g. Italy, Greece and Turkey) is the result of high seismic hazard combined with densely populated areas (exposure) and ageing of the building heritage. This is often characterised by deficiencies in anti-seismic design and poor construction quality (vulnerability), considering that significant progress in this field has only recently been achieved. From the environmental perspective, buildings as a whole are one of the main causes of climate change, being responsible for 34% of global energy demand and 37% of CO₂ emissions.

In response to the dual need to mitigate seismic risk and reduce the carbon footprint, a series of different timber-based reinforcement solutions have been developed in recent years. Such solutions include strong-backs, CLT panels and hybrid systems, which have shown promising results. These solutions enable the improvement of the structural and energy performance of buildings through the integration of structural reinforcement with insulating materials. They also reduce the invasiveness of reinforcement thanks to the lightness and compatibility with historical materials and minimizes the environmental impact through wood's inherent sustainability.

However, it should be noted that existing solutions still have some critical limitations, including high costs, a limited degree of prefabrication, and poor adaptability during construction phases.

To overcome these limitations, a new timber-based solution called TimberGrid was developed within the SAFER-REBUILT project (funded by the European Union - Next Generation EU, Mission 4, Component 2, CUP H93C22000610002).

The system consists of a timber lattice structure composed of columns, beams and diagonals, which are connected by screws and carpentry joints. The lattice is anchored to the existing masonry using diffuse dowel-type fasteners (at approximately 4-5 m²) and connected to the base by means of anchor connections, typical of platform-type structures (e.g. hold downs and angles). The TimberGrid project has been developed with the aim of improving the seismic safety and energy performance of unreinforced masonry buildings (URM), through rapid and minimally invasive intervention (social sustainability), using "less-engineered" timber products from short supply chains (economic sustainability), easier waste management and recycling of materials (environmental sustainability).

In order to identify the best grid layout and the most effective joint configurations, an extensive numerical analysis was conducted. Firstly, a simplified approach was used with the finite element software SAP2000, where failure modes of the URM wall to be strengthened were imposed by the authors for an initial verification of the solution's effectiveness. Then, to support the results from the simplified approach, a detailed numerical model was created using the finite element software Midas FEA NX.  

This paper presents the outcomes of the TimberGrid reinforcement system development process, optimised for existing unreinforced masonry structures, aiming at enhancing the effectiveness of current timber-based strengthening techniques. Numerical analyses were crucial for calibrating the full-scale experimental tests planned within the project and for designing the relative test set-up.