Reduction of the lateral thrust of masonry arches and vaults with FRP composites

Fiber-reinforced polymer (FRP) composites are being increasingly used for rehabilitation and strengthening of masonry structures and, in particular, to strengthen masonry arches and vaults against their most critical failure mechanisms. The FRP reinforcement, introducing tension resistance, allows the line of thrust to fall outside the thickness of the arch. This fact has two important consequences: the capacity of the arch itself is increased, and the lateral thrust transmitted to the piers is reduced, thereby increasing the capacity of the "arch + piers" system. While the first effect has been stressed by existing research, less attention has been paid to the second effect, which nevertheless is very important for practical applications. In this paper, the effect of bonding an FRP sheet to the intrados of a circular arch on the minimum value of the lateral thrust is evaluated analytically. The model is then applied in particular to the four lateral arches of an edge vault. Edge vaults are a valuable part of the architectural and cultural heritage of some regions of Italy, and are structurally similar to cross-vaults except for the presence of a double-curvature shell portion in the middle of four barrel webs. These vaults are usually subjected to symmetric loading, as a result of the large dead-to-live load ratio. Hence, collapse of a vault typically occurs when no tie-rods or tie-beams are adopted and the piers are unable to bear the thrust of the vault. The paper also illustrates results of an experimental investigation on masonry edge vaults strengthened with FRP composites and subjected to uniform loading with measurement of the lateral thrust. Test results and theoretical predictions are presented and discussed.