The University of Newcastle, Centre for Infrastructure Performance and Reliability
Helifix (Australia) Pty Ltd, Alexandria

An experimental study was conducted to assess the effect on strength and ductility of retrofitting unreinforced masonry (URM) shear panels with stainless steel, high stress, twisted reinforcement bars. The reinforcement bars were attached to the shear panels using the near surface mounting (NSM) / structural repointing (SR) technique in which thin slots are cut into the surface of the masonry and the reinforcement is bonded into the slots using high bond strength, thixotropic, injectable cementitious grout. A total of ten wall panels (1200 mm x 1200 mm); two URM and eight with different quantities and orientations of reinforcement, were tested in diagonal tension/shear in accordance with ASTM E519-02 [1]. Four different reinforcement schemes (two repeats per scheme) were examined. Three of the schemes used vertical reinforcement (perpendicular to the bed joints) near surface mounted into the brick material and evenly distributed between both faces of the wall with reinforcement ratios 0.04%, 0.09% and 0.18% respectively. The remaining scheme used horizontal reinforcement structurally repointed into the bed joints and evenly distributed between both faces of the wall with a reinforcement ratio 0.04%.
The results are compared with tests conducted previously by the authors on URM and Fibre Reinforced Polymer (FRP) retrofitted panels, using the same masonry. The FRP study used panels of the same size and tested in the same way. The FRP study investigated a variety of reinforcement arrangements which included vertical, horizontal and combined systems and single and double sided reinforcement. The reinforcement ratios used in the FRP study were either 0.06% or 0.13%.
It was observed that significant increases in strength and ductility (particularly the latter) can be achieved using the stainless steel reinforcement compared to URM and that the stainless steel strengthened panels performed comparably with the FRP strengthened panels. The broader aim of the research is to identify techniques for improving the seismic performance of existing URM walls under in-plane shear loading.

Key words
Masonry; strengthen/retrofit; shear; stainless steel reinforcement