In-Plane Shear Strengthening of Masonry Wallettes Using Ultra-High Performance Concrete Precast Plates

Abstract

This paper presents the outcomes of a comprehensive experimental investigation aimed at characterizing the in-plane shear strength of Unreinforced Masonry (URM) wallettes subjected to diagonal compression. The study focuses on the strengthening of these wallettes using precast Ultra-High Performance Concrete (UHPC) diagonal strips, externally bonded onto the wall substrates through high-strength epoxy mortar. Twenty-three wallettes, each measuring 1000 mm × 1000 mm × 70 mm, were meticulously constructed and subjected to in-plane diagonal compression. Among these, eighteen wallettes underwent strengthening utilizing various configurations of UHPC, with a key emphasis on variables such as UHPC strip width and thickness, substrate nature, and corner confinement with enlarged UHPC rectangular plates. Findings from the experimental program highlighted the significant influence of UHPC retrofit parameters on the wallettes performance. Notably, corner confinement emerged as an effective strategy against premature toe crushing failure, enhancing the wallettes ability to withstand higher in-plane compressive loads. While UHPC strip width exhibited moderate impact, UHPC strip thickness emerged as a dominant factor. Increasing strip width from 100 to 250 mm yielded an approximate 8% shear strength improvement, whereas doubling strip thickness from 10 to 20 mm led to a substantial 27% enhancement. Notably, enhanced strip width demonstrated pronounced benefits in terms of ductility and energy dissipation capacity. Excessive UHPC retrofit thickness induced brittle failure despite escalating shear strength. Conversely, thinner UHPC retrofits achieved a favorable balance between strength, ductility, and energy dissipation. Wallettes retrofitted with 5 mm UHPC exhibited an impressive 2.36-fold shear strength increase compared to reference walls, while those with 10 mm and 20 mm UHPC retrofits experienced 2.14 and 2.78-fold improvements, respectively. Furthermore, the manner of UHPC application significantly influenced the strengthening system's behaviour. For identical strengthening layouts, the direct bonding of UHPC onto masonry substrates resulted in a 25% increase in shear strength compared to UHPC bonding onto plaster overlays.