STRENGTHENING OF MASONRY VAULTS WITH STEEL REINFORCED GROUT

Abstract

In a period characterized by the urgent need of ensuring an adequate safety level to the building stock, including architectural heritage, Steel Reinforced Grout (SRG), comprising Ultra High Tensile Strength Steel cords embedded in a mortar matrix, is emerging as a particularly advantageous solution for the externally bonded strengthening of existing structures. Nevertheless, its development is still at a relatively earlier stage with respect to the already well-established Fibre Reinforced Polymers (which make use of organic matrices) as well as to other mortar-based composite materials, such as Textile Reinforced Mortars or Fabric Reinforced Cementitious Matrix (which comprise carbon, glass, basalt or PBO meshes). Therefore, a deep knowledge needs to be gained on mechanical properties, acceptance criteria and behaviour of reinforced structural members in order to develop suitable design relationships and assessment criteria, which would allow for a more confident use of SRG in structural rehabilitation practice. This work provides a wide experimental evidence of SRG composites with lime-based mortars for the reinforcement of masonry vaulted structures. First, direct tensile tests on bare textile specimens and SRG coupons as well as single-lap shear bond tests were performed to investigate the main mechanical properties (tensile strength and stiffness, crack pattern, cordto- matrix and SRG-to-substrate load transfer capacity, failure modes) and derive fundamental acceptance and design parameters. Then, bond tests were performed on curved substrates to investigate the influence of convex and concave curvatures on the SRG-to-masonry bond behaviour. Both double-lap double-prism test and three point bending tests were performed to study intermediate debonding mechanisms and analyse the effect of testing setups. Simplified relationships were also derived that account for substrate curvature, which may be useful for a preliminary estimate of SRG bond stregnth. Finally, full-scale tests on masonry vaults reinforced either at the extrados or at the intrados with different SRG systems were carried out. Specimens were provided with buttresses and backfill. Reinforcements included connectors at the abutments or along the barrel vault. The use of unconventional measurement techniques, such as the digital image correlation, provided information on crack occurrence and arch-fill interaction. Test outcomes revealed the effectiveness of SRG in improving the load-carrying and the deflection capacity of masonry arched members.