Behavior and retrofitting of single-leaf vaults under distributed horizontal forces

In this paper, the seismic vulnerability of single-leaf vaults undergoing horizontal actions is discussed, and an innovative strengthening technique is proposed. The extreme vulnerability of these structures was frequently assessed after recent earthquakes, when a significant number of single-leaf vaults collapsed, regardless of the earthquake intensity and of the level of the structure global damage; and highlights the need for structural strengthening interventions. In this paper, the vault seismic vulnerability is discussed based on the results of an experimental study on the behaviour of a single-leaf vault subjected to cyclic unsymmetrical loads. A special testing bench is adopted, which allows tilting the specimen both clockwise and counter-clockwise. In the tilted position, each vault segment is subjected to both relative vertical and horizontal forces, corresponding to the gravity load force components evaluated along and normal to the tilted axis. The resulting load distribution simulates the seismic action acting on the vault ring. Furthermore, lightweight ribs are proposed as an innovative solution to upgrade the seismic performance of existing single-leaf vaults. Ribs can be designed to behave like external retaining structure, preserving the vault shape by constraining the uplift deflection in the case of unsymmetrical load conditions. Further experimental tests will assess the efficiency of the proposed lightweight rib reinforcement solution, and clarify the role of the reinforcement-to-vault connection.