Author

Jared L Brown

Issuing Body

Mississippi State University

Advisor

Howard, Isaac L.

Committee Member

Woodson, Stanley C.

Committee Member

Foust, Bradley W.

Committee Member

Freyne, Seamus F.

Date of Degree

12-1-2020

Document Type

Dissertation - Open Access

Major

Civil Engineering

Degree Name

Doctor of Philosophy

College

James Worth Bagley College of Engineering

Department

Department of Civil and Environmental Engineering

Abstract

Concrete is among the most common materials utilized to construct protective elements in hardened structures. Subsequently, understanding how a concrete member will respond to explosively driven fragment or projectile impact is critical to the protective design process. Explosively driven fragments can have many different shapes and sizes depending on the event that resulted in their creation. These geometric variations can include a high-aspect, or width to thickness, ratio; however, impact from fragments with elevated aspect ratios on hardened concrete has not been extensively studied. Therefore, reinforced concrete specimens were subjected to impact from fragments with different aspect ratios to illustrate and quantify the effect of fragment characteristics, protective element features, and experimental target size on local impact performance. A novel experimental technique was developed to allow for high-aspect ratio fragment impact on concrete slabs to be evaluated. The same concrete materials were also impacted with lower aspect ratio fragments for comparative purposes. Data collected from these two experimental series were utilized to analyze the effects of compressive strength, thickness, and fiber reinforcement on impact performance. The accuracy of existing penetration and spall prediction methodologies were evaluated for both fragment types. The kinetic energy required to cause reinforced concrete to present a breached condition due to the high-aspect ratio fragment was also analyzed. Modifications were made to existing contact charge equations to account for differences between the contact charge energy required to cause a breach condition and that required from fragment impact to produce a breach condition. The breach envelope defined by these relationships was further evaluated using a computational model calibrated specifically for this impact scenario. Finally, the effect of impact specimen geometry and confinement type on target performance was numerically evaluated. Artificial and inertial confinement were examined through varying target diameter to projectile diameter ratio with and without artificial circumferential confinement. Given the minimal data associated with local effects of high-aspect ratio fragment impact and the many factors that can influence concrete impact resistance, the information and relationships learned along with the analysis techniques developed herein can be utilized to improve the state of the art of protective design.

URI

https://hdl.handle.net/11668/20806

Sponsorship

US Army Engineer Research and Development Center

Comments

impact||concrete||impactor aspect ratio||confined concrete target

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