Development of braided fibrous materials for retrofitting masonry infil walls

Abstract

The most recent earthquakes in Turkey, Italy and Spain demonstrated the vulnerability of non loadbearing unreinforced masonry walls acting as infill of reinforced concrete frames. Conventional fibre reinforced composites (FRPs), which are used to strengthen masonry walls to improve their resistance towards seismic collapse, present insufficient adhesion and delamination problems that limit their full strengthening potential. To address this issue, the main focus of this work was to develop a strengthening system based on novel fibrous structures (braided structures with axial reinforcement) that will provide very good adhesion with cement mortar (used to incorporate these structures within masonry) and, will present excellent ductility in order to sustain the structure of masonry walls after a seismic event, avoiding complete splitting and collapse. Different braided fibrous structures were produced with different surface characteristics (different spacing between the surface ribs). The adhesion between these braided structures and cement mortar was characterized using pull-out tests and according to the experimental results, the braided structures produced by replacing two polyester braiding yarns with polyester braids and produced at higher take up speed showed excellent adhesion with the mortar, leading to complete breakage of these structures before being pulled out. Moreover, tensile testing of these structures revealed very good ductile behaviour and tailorable mechanical properties (strength, stiffness and ductility) depending on the composition of axial reinforcing fibres.