Kim, JimmyAlatify, Ali2024-12-172024https://hdl.handle.net/20.500.14154/74278Abstract This dissertation studies different aspects of the interfacial behavior of composite reinforcement embedded in concrete. GFRP rebars are known for its none-corrosiveness, light weight, and high strength compared to conventional steel rebars, and became predominantly employed in different structural applications such as bridge construction. Thus, the serviceability and interfacial behavior of GFRP bars in different structural applications is investigated in four phases in this research. Chapter three presents an experimental study on the residual bond of glass fiber reinforced polymer (GFRP) rebars embedded in ultra-high performance concrete (UHPC) subjected to elevated temperatures, including a comparison with ordinary concrete. Based on the range of thermal loading from 25oC (77oF) to 300oC (572oF), material and push-out tests are conducted to examine the temperature-dependent properties of the constituents and the behavior of the interface. Also performed are chemical and radiometric analyses. The average specific heat and thermal conductivity of UHPC are 12.1% and 6.1% higher than those of the ordinary concrete, respectively. The temperature-induced reduction of density in these mixtures ranges between 5.4% and 6.2% at 300oC (572oF). Thermal damage to GFRP, in the context of microcracking, is observed after exposure to 150°C (302°F). Fourier transform infrared spectroscopy reveals prominent wavenumbers at 668 cm-1 (263 in.-1) and 2,360 cm-1 (929 in.-1), related to the bond between the fibers and resin in the rebars, while spectroradiometry characterizes the thermal degradation of GFRP through diminished reflectivity in conjunction with the peak wavelength positions of 584 nm (2,299×10-8 in.) and 1,871 nm (7,366×10-8 in.). The linearly ascending bond-slip response of the interface alters after reaching the maximum shear stresses, leading to gradual and abrupt declines for the ordinary concrete and UHPC, respectively. The failure mode of the ordinary concrete interface is temperature-sensitive; however, spalling in the bonded region is consistently noticed in the UHPC interface. The fracture energy of the interface with UHPC exceeds that of the interface with the ordinary concrete beyond 150oC (302oF). Design recommendations are provided for estimating reductions in the residual bond of the GFRP system exposed to elevated temperatures. The interface shear between ordinary concrete and ultra-high-performance concrete (UHPC) connected with glass fiber reinforced polymer (GFRP) rebars is presented in chapter four. Following ancillary tests on the fracture of the rebars under in-plane shear loading, concrete-rebar assemblies are loaded to examine capacities and failure modes that are dependent upon the size, spacing, and number of the rebars. While the transition of load-resisting axes in the glass fibers and their quantity dominates the shear behavior of the bare rebars, the size and spacing of the reinforcement control the capacities of the interface by altering load-transfer mechanisms from the rebar to the concrete. The degree of stress distribution affects the load-displacement response of the interface, which is characterized in terms of quasi-steady, kinetic, and failure regions. The primary failure modes of the interface comprise rebar rupture and concrete splitting. The formation of cracks between ordinary concrete and UHPC results from interfacial deformations, leading to spalling damage when applied loads exceed service levels. An analytical model is formulated alongside an optimization technique. The capacities of the interface in relation to the rebar rupture and concrete splitting failure modes are predicted. Furthermore, a machine learning algorithm is utilized to define a failure envelope and propose practice guidelines through parametric investigations. The serviceability of concrete beams with continuous and spliced glass fiber reinforced polymer (GFRP) rebars is investigated and detailed in chapter five. An experimental program is undertaken using 18 beams incorporating various reinforcing schemes to examine the effects of rebar distribution and spacing on flexural and cracking responses. The cracking load of the beams with the continuous rebars (Category C) is 24.2% higher than that of the beams with the spliced rebars (Category S) experiencing stress concentrations. The distributed configuration of the rebars enhances interactions between the concrete and reinforcement, thereby increasing bond transfer in the beams. Contrary to the linear load-displacement behavior of the C-category beams after cracking, parabolic trends are observed in the S-category beams owing to the slip of the spliced rebars, which degrades composite action at the rebar-concrete interface and reduces the flexural rigidity of the beams. The crack opening of the C-category beams under service loading is within the tolerable limits of published guidelines, whereas the opening of the S-category beams exceeds the limits. Through statistical characterization, the significance of the rebar distribution in crack opening and depth is demonstrated at a 5% significance level (95% confidence interval). Design recommendations include a slip multiplier of 0.63 for calculating the stress of spliced GFRP rebars and a bond coefficient of 0.88 for determining the flexural capacity of beams with this type of reinforcement. The implications of variable bond for the behavior of concrete beams with glass fiber reinforced polymer (GFRP) bars alongside shear-span-dependent load-bearing mechanisms is evaluated in chapter six. Experimental programs are undertaken to examine element- and structural-level responses incorporating fully and partially bonded rebars, which are intended to represent sequential bond damage. Conforming to published literature, three shear-span-to-depth (av/d) ratios are considered: arch action (av/d < 2.0), beam action (3.5 ≤ av/d), and a transition from arch to beam actions (2.0 ≤ av/d < 3.5). When sufficient bond is provided for the element-level testing (over 75% of 5db, where db is the rebar diameter), the interfacial failure of GFRP is brittle against a concrete substrate. An increase in the shear-span-to-depth ratio, aligning with a change from arch action to beam action, decreases the load-carrying capacity of the beams and the slippage of the partially bonded rebars dominates their flexural stiffness. Compared with the case of beams under beam action, the mutual dependency of the bond length and shear span is apparent for those under arch action. As far as failure characteristics are concerned, the absence of bond in the arch-action beam prompts crack localization; by contrast, partially bonded ones demonstrate diagonal tension cracking adjacent to the compression strut that transmits applied load to the nearby support. The developmental process of rebar stress is dependent upon the shear-span-to-depth ratios and, in terms of utilizing the strength of GFRP, beam action is favorable relative to arch action. Analytical modeling suggests design recommendations, including degradation factors for the calculation of rebar stresses with bond damage when subjected to arch and beam actions.203en-USBondserviceabilityGFRPUHPCInterfacemachine learningarch actionbeam actionspliced beamspushout testThesis