Unreinforced Masonry (URM) Walls Retrofitted with Reinforced Polyurea for Blast Load Protection

Abstract

Unreinforced masonry (URM) walls are commonly used in the construction of buildings both as external walls and internal partitions because they are cost-effective and meet many functional building requirements. However, URM walls have low flexural capacity as they are designed to resist gravity loads. This weakness and their brittle nature make them extremely vulnerable to blast loads when exposed to accidentally or intentionally generated shock waves. Consequently, their failure mode could be catastrophic, collapsing quickly and disintegrating into fragments of high-impact velocities capable of causing severe injury and death to occupants and damage to the contents of buildings. Thus, improving the performance of these walls against explosions has become necessary for public safety. As such, this research attempts to provide a possible way of enhancing the wall resistance to blast attacks using reinforced membrane retrofits.

The research has two phases: experimental and analytical. The experimental work involved tests of six URM walls, consisting of four concrete masonry unit (CMU) and two stone walls. The dimensions of each wall were 2 meters by 2 meters, and it was built with 4-inch hollow blocks for the CMU walls and solid concrete stone blocks for the stone walls. The walls were categorized into non-load bearing and load bearing, with two CMUs and one stone wall in each category. Also, they were retrofitted with the combination of two materials: the XS-350 polyurea and SS304 welded 76.2 mm x 76.2 mm stainless-steel wire mesh with either 4.1 mm or 3.1 mm wire diameters.

The retrofitted walls were exposed to blast loads of varying intensity during the tests using a shock tube. The test parameters included the percentage of stainless-steel mesh, type of URM, axial loading, arching action, and pressure-impulse combinations. The results were assessed using dynamic mid-height deflections, failure mode, ductility, load-carrying capacity, and energy absorption capacity. The analytical research involved developing resistance functions and single-degree-of-freedom (SDOF) dynamic inelastic analyses. The SDOF models predicted the dynamic mid-span deflection of the hardened URM walls reasonably well, illustrating the effectiveness of the analysis technique for blast load analysis. A parametric investigation was carried out with varying wall thickness, axial load, aspect ratio, and percentage of steel. Finally, a design procedure was developed for use in engineering practice.