Date of Award

2017

Document Type

Open Access Thesis

Department

Civil and Environmental Engineering

Sub-Department

College of Engineering and Computing

First Advisor

Fabio Matta

Abstract

The aim of this project is to investigate a novel and affordable option to externally strengthen substandard concrete masonry (CM) walls for out-of-plane loads (e.g., high winds and flying debris). Two types of strengthening materials for fiber-reinforced cement mortar (FRCM) overlays are investigated; namely, fishing net (FN) and welded wire steel mesh (WWSM) reinforcements.

Salient mechanical properties of representative materials including substandard concrete masonry unit (CMU) blocks, mortar, nylon FN and WWSM reinforcements, and FRCM composite, were experimentally characterized. A simple bilinear model is proposed to describe the tensile behavior of the FRCM composite. An analytical model was then used to estimate the flexural capacity and failure mode of strengthened CM walls as a function of the amount of FN reinforcement. The wind velocity that a strengthened CM wall can withstand was evaluated based on a standard velocity pressure equation, and a parametric study was performed to determine the influence of the CM compressive strength (as a measure of substandard properties) on the out-of-plane flexural capacity.

Finally, an experimental program was implemented to provide a proof of concept. A four-point bending test was implemented on four concrete masonry specimens, including: one plain masonry (control) specimen; two specimens strengthened with one and two layers of FN-reinforced mortar overlay, respectively; and, one specimen strengthened with a WWSM-reinforced mortar overlay, which served as benchmark specimen for the newly-conceived FN system.

It is shown that the out-of-plane flexural capacity of substandard CM walls can be made suitable to resist high wind pressures by means of FN- as well as WWSM-FRCM overlays. In fact, the out-of-plane capacity contributed by the FN-FRCM system is comparable to that contributed by the WWSM-FRCM counterpart. However, the FN-FRCM overlay outperforms the WWSM system in term of deformability and thus energy-absorption capacity. The evidence produced through this research attests to the potential of the novel FN-FRCM system presented herein to retrofit substandard CM walls against high-wind pressures, and possibly the impact of flying debris during hurricanes and tornadoes.

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