Comparison of Double-Lap/Double-Prism and Single-Lap/Single-Prism Shear Tests for the TRM-to-Masonry Bond Assessment

The efficient use of Textile Reinforced Mortar (TRM) overlays as a strengthening means of structurally deficient built facilities depends on the bond between the externally bonded grids and the existing substrate. Different types of experimental set ups have been used for the investigation of the bond mechanism of TRM strips externally bonded on masonry (and other) substrates including double-lap/double-prism, single-lap/single-prism and double-lap/single-prism configurations. This paper presents the results of an experimental program aiming to assess the bond characteristics of interfaces comprising glass fiber textile reinforced cementitious mortars applied as overlays on solid clay brick unreinforced masonry wall prisms. For this purpose, both double-lap/doubleprism and single-lap/single-prism shear tests were employed, providing the basis of a comparison between the two test set ups. Double-lap/double-prism specimens are heavier, more labor-intensive and of higher handling care demand than single-lap/single-prism ones but are thought to better simulate actual shear bond phenomena. For the specific interfaces dealt with herein, a common failure mode (textile slippage) was observed for both test set-ups. The results obtained demonstrate that maximum load values derived from both test set-ups are comparable. Nevertheless, this does not apply to relative displacement values which bear a strong dependence on the different load introduction means and (where applicable) on the assumptions made for their computation.