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<p>  </p> <p>The use of headed reinforcement in concrete has found an increasing interest in construction applications. From shear reinforcement in walls to longitudinal reinforcement in beams and columns, there is a growing need to understand the behavior of headed rebars. A headed rebar is a deformed bar with a head attached to its end and while similar anchorage devices such as headed studs and hooked rebars are well established in theory with design equations developed, headed reinforcement lack this level of knowledge and hence, their application in industry is limited.</p> <p>Current code provisions such as fib Model Code 2010 allow the design of headed rebars as (1) a hooked bar, (2) a headed stud, and (3) using experimental results. Moreover, ACI 318-19 only contains a design equation for the development length of headed rebars but not its capacity. While the literature has justified the approximation of the capacity of headed rebars with hooked bars through a multitude of studies comparing both anchorage devices. Such a justification is not well-founded for headed studs due to a scarcity of studies comparing headed rebars to headed studs. Moreover, there is a lack of design equations accurately predicting the behavior of headed rebars in several parameters. All these issues emanate from the complexity of headed rebars due to their joint mechanism of anchorage coming from both resistance along the rebar deformations and bearing on the head.</p> <p>This study aims to better understand the behavior of headed bars by numerically analyzing the influence of different parameters on their performance. Furthermore, direct comparisons are made between headed reinforcement, headed studs, and straight bars to segregate the effect of the bond along the shaft and the bearing at the head on the behavior of headed bars. </p> <p>The parameters included in this study are embedment depth, edge distance, and concrete compressive strength. The numerical models are verified using a 3D non-linear finite element software MASA (Macroscopic Space Analysis) which employs the microplane model with relaxed kinematic constraint as the constitutive laws of concrete. Two numerical approaches, which differ only in the interface properties between the head and concrete, are validated against experimental results before carrying out the parametric study. Several properties including head, concrete, and bond stresses, along with ultimate capacities and crack patterns are extracted from the models and analyzed. Moreover, the load-displacement graphs of headed rebars, studs, and straight rebars are compared and contrasted. Assessments and theories about the discrepancies between the behavior of headed studs and rebars are stipulated. Finally, potential methods for formulating design equations are proposed for future studies.</p>

<p> A research program is presented for assessing the plastic collapse load and incremental collapse load of reinforced concrete frames. This investigation attempts to establish a range of validity of simple plastic theory when applied to the under reinforced concrete frames and to determine the sensitivity of such structures to variable repeated loading. </p> <p> An experimental program was conducted on 4 reinforced concrete frames and two reinforced concrete columns. Deflections and strains of these models of nearly prototype size were measured and compared with predicted values at critical cross-sections. </p> <p> Resulting conclusions and recommendations for further research are made. </p> / Thesis / Master of Engineering (MEngr)

Simplified mechanical loading paths, which represent more complex loading paths observed during penetration, were investigated using a triaxial chamber and a high-strength concrete. Objectives were to determine the effects that stress/strain (load) paths had on the material’s unconfined (UC) residual strength. The loading paths included hydrostatic compression (HC), uniaxial strain in compression (UX), and uniaxial strain load biaxial strain unload (UXBX). The experiments indicate that load paths associated with non-visible microstructural damage were HC and UX, which produced minimal impact on the residual UC strength (<30%), while the load paths associated with visible macro-structural damage were UXBX, which significantly reduced the UC strength (>90%). The simplified loading paths were also investigated using a material model driver code that was fit to a widely used Department of Defense material model. Virtual experiment data revealed that the material model investigated overestimated material damage and produced poor results when compared to experimental data.

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.

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