Stabilization of Masonry Arches by Hidden Prestressing Cabels with the Possibility of Clearence the Space by Removing the Forged Tie Rod

Stabilization of baroque masonry structures with flat arches by longitudinal prestressing can be advantageously carried out by deliberately introducing a system of prestressing forces into the structure so that the normal effects of the prestressing force exceed the radial effects. Then the arch is transformed into a prestressed tie beam with a curved centreline. Additional prestressing is possible by the method of substitute cable ducts. Then the construction of the masonry arch becomes a prestressed tie rod supporting the wall pillars and even preventing their further spreading, as happens with the original and unprestressed arch. The paper is addressed to the professional community, which, especially in the field of monumental Baroque masonry structures, often deals with failures of masonry arches and vaults. These structures are usually broken by cracks in the top. The supporting structures must resist the long term arching force, which has an oblique direction. While its vertical component creates no problems, the horizontal component of the arc force is considerable and, in addition, acts in the long term already to load the dead weight of the vaulted structure. Horizontal displacements at the base of the vault (of the supports) are the most prevalent failures, accompanied first by the formation of transverse cracks in the top section of the vault. Stabilization is a key step for their permanent rehabilitation. By the additional prestressing, the structure supported by the supports becomes a prestressed tie rod, which in turn prevents further failure development until the pressure reserve is exhausted. The method is so effective that it even allows the original forged tie rod to be removed. The removal of the forged rod of the masonry arch is an example of the high efficiency of the described method. It is a former Baroque granary adapted into a living space. Two roughly elliptical arches of brickwork of 300/600mm top section span the space with clearances of 6.0m and 6.3m. The masonry is made of solid bricks with lime mortar. The passage height under the arches was insufficient, only 1.72 m. It was raised to 2.4 m after the arch was prestressed and the forged tie rod removed. The paper contains examples of the structural design, realization and measurement of the deformation response of the structure. The method can be effectively used to stabilize masonry arches in the case of low stiffness of supports or to free space by removing a forged tie rod. Measurements of the implemented structure show its effectiveness and long-term reliability.