Evaluation of the effect of full and partial retrofit of timber floors in an urban masonry cluster building

Understanding the seismic response of retrofitted urban masonry clustered buildings (UMCBs) is essential for post- earthquake reconstruction planning, as highlighted by the 2009 L’Aquila and 2016 Central Italy events. This study investigates the effectiveness of floor strengthening by replacing existing timber floors with reinforced concrete slabs, using finite element modeling in DIANA FEA. The retrofit is analyzed both in a single unit—varying the number and position of strengthened floors—and in the full cluster, where only some units are retrofitted. The case study is a UMCB in Castelsantangelo sul Nera, damaged by the 2016 earthquake. Results from non-linear static analyses and tensile strain distributions show that partial strengthening by position offers limited benefits, and strenghtening only the roof may worsen the response. Increasing the number of replaced floors improves shear capacity almost linearly. However, retrofitting the entire cluster with concrete slabs reduces displacement capacity compared to additional sheathing solutions. Strengthening isolated units within a cluster leads to unrealistic base shear increases in adjacent units. Future work will implement discontinuities among units to better capture inter-unit interactions and explore more compatible retrofit strategies that preserve the original seismic behaviour.