Dissertations and Theses

Date of Award


Document Type



Civil Engineering

First Advisor

Ardavan Yazdanbakhsh


Concrete, discrete reinforcing element, FRP, experiment, wind blade, rebar


This dissertation presents a study that led to the development of slender elements that look like fibers used for reinforcing concrete but with a very different reinforcing mechanism. These elements, referred to as “Needles” are very rigid and strong; when intersected by growing cracks in concrete under heavy and increasing loads, they do not break and deform minimally. In the present work major steps were taken to understand the reinforcing mechanism of Needles. In addition, to investigate the influence of Needles on the mechanical performance of concrete incorporating Needles, at both material and structural levels, a series of laboratory experiments and simulations of concrete incorporating Needles with different physical characteristics were designed and conducted. The investigated physical characteristics of Needles include size and overall geometry. The study focused on glass fiber reinforced polymer (GFRP) composites as the material for producing Needles. Although other materials can be used for producing Needles, GFRP materials were chosen for their unique mechanical properties, particularly, very high values of tensile strength and stiffness.

The findings of the study revealed that GFRP Needles increase the tensile strength and post-failure toughness of concrete significantly without any negative impact on concrete’s workability, stability, and compressive strength. The orientation of glass fibers in Needles has a strong correlation with reinforcing performance of the Needles. The performance is at maximum level when all the fibers are aligned with Needle’s axis. Compared with the FRP Needles, FRP fibers (which are smaller and slenderer than Needles) can significantly increase the toughness of concrete beam. Many other laboratory test results revealed that the Needles improve the performance of concrete members significantly regardless that more possibilities of size and geometry of needle are yet to be experimented. Because the number of experiments required to determine optimal geometries of Needles is prohibitively large for a laboratory setting, finite element method (FEM) and a concrete damage model were integrated to simulate the performance of GFRP Needles with different geometries in concrete. The simulation focused on the post cracking tensile strength of concrete. Probability theory was employed to model the orientation and location of Needles as random variables.



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