Structural enhancement of low strength masonry using retro-reinforcement

Abstract

One of the most effective ways of achieving sustainable construction is to extend the life of an existing structure by repair or strengthening. This needs to be carried out at minimal cost and with minimal disruption to the owners or end users without creating a future maintenance liability. In the case of masonry buildings this can be achieved with the use of retro-reinforcement. Retro-reinforcement involves the installation of small diameter reinforcing bars into pre-cut grooves or pre-drilled holes in the near-surface zones of the masonry that are likely to be subject to tensile stress. The reinforcement usually consists of stainless steel bars to minimise the risk of corrosion. The principal objectives of adding such reinforcement are to improve flexural crack control, increase flexural and shear strength and to increase robustness and ductility. In the UK the technique has been used extensively to strengthen the masonry cladding of low to medium rise buildings, particularly where cracking has occurred adjacent to a long-span window or similar opening. This paper summarises recent experimental research into the behaviour of clay brick wall panels containing 2m and 3m span openings. Single leaf walls with different arrangements of reinforcement constructed using very low strength (1:12 cement:sand) mortar were tested under short-term in-plane vertical loading. Similar plain and retro-reinforced wall panels constructed from natural hydraulic lime (NHL2) mortar were also tested. Some of the panels were constructed to simulate damage (cracking and excessive deflection) that occurs in practice. The retro-reinforced walls showed increases in strength of between 59% and 206% when compared with the unreinforced experimental controls. In addition, the load at which first visible cracking occurred and the reserve of strength beyond first cracking were enhanced.