Date of Defense
28-4-2026 10:00 AM
Location
F3-234
Document Type
Thesis Defense
Degree Name
Master of Science in Civil Engineering (MSCE)
College
COE
Department
Civil and Environmental Engineering
First Advisor
Dr. Ahmed Bediwy
Keywords
Shape memory alloy, anchorage, slip, bond behavior, Taguchi, experimental study.
Abstract
The anchorage and bond behavior of smooth-surfaced Shape Memory Alloys (SMAs) is investigated in this thesis, but specifically, the focus will be on Nitinol (Ni-Ti). Nitinol has distinctive properties, including Superelasticity Effect (SE) and Shape Memory Effects (SME). These properties make Nitinol bars suitable for civil and seismic engineering applications that require resilience and durability. However, Nitinol rebars possess a smooth surface, making it difficult to achieve adequate bonding and anchorage, potentially altering their load-carrying abilities. This inadequate anchorage and bonding restrict their use in the field of structural and seismic engineering. The main aim of this study is to investigate the anchorage mechanism and bond behavior of smooth-surfaced Nitinol bars embedded into concrete with emphasis on optimization of the performance of the two proposed anchorage systems. The experimental program is divided into two phases (Phase I and Phase II), where Phase II is dependent on the results of Phase I. Phase I experimentally evaluates the efficiency of two feasible wedge-type anchorage systems, Wedge-and-barrel (WB) and Spring anchor (SA), which are typically utilized in post-tensioning applications, and assesses their capabilities of anchoring smooth-surfaced Nitinol SMA rebars. A monotonic tensile testing regime consisting of 24 unique configurations was performed at different maximum strain levels (6%, 8%, and 10%) and loading rates (0.5, 2, 5, and 10 mm/min). The findings validate that the two anchorage systems illustrated consistent superelastic stress-strain responses. Significant performance differences were observed, wedge-and-barrel anchorage system showed increased stress capacity, improved load-transfer efficiency, and consistency across replicated tests, which can be attributed to its greater mechanical confinement and frictional interlock. The wedge-and-barrel anchorage system exhibits an increase of approximately 25% stress capacity compared to the spring anchorage system. On the other hand, the spring anchorage system exhibited good anchorage performance, with a slightly lower stress response and greater variation at higher levels of deformation due to the spring's compression mechanism. Phase II, a Taguchi-based optimization approach is experimentally applied to evaluate the bond behavior of smooth-surfaced Nitinol SMA rebars embedded in concrete. Five key parameters were considered: concrete cover (85, 90, 95, and 100 mm), concrete compressive strength (25, 40, 55, and 70 MPa), embedment length (100, 125, 150, and 175 mm), surface coating (smooth/none, rough epoxy, 300-μm sand coating, and 600-μm sand coating), and anchorage type (none, epoxybased anchor, spring anchor and wedge-and-barrel anchor). A L16 Taguchi orthogonal array was utilized to define 16 distinct specimen configurations, each configuration replicated three times to ensure reliability in the experimental results. Direct pull-out tests were conducted to evaluate bond strength, stress–slip response, and failure modes. An analysis of variance (ANOVA) was conducted, indicating that the anchorage type is the dominant parameter affecting the bond behavior of SMA, with a contribution of 83%. The wedge-and-barrel anchorage system has been found to be the optimum anchorage system among other systems under consideration, reaching a maximum bond stress of 6.334 MPa at a maximum slippage value of 2.03 mm. The Taguchi signal-to-noise analysis enabled the identification of which parameters have the most significant impact and which level combination yields the highest bond capacity. A predictive model was developed using the Taguchi approach. It was proven reliable, as the predicted optimal and additional specimens' bond response agreed with the experimental results, showing a maximum error of 10.3% across all specimens.
The outcomes of the experimental testing will give significant information on applying the smooth-surfaced Nitinol bars in the concrete and steel structures, which will contribute to the knowledge of their anchorage behavior. These results provide a base for further research in the field of optimizing Nitinol reinforcement in structural and seismic projects.
Included in
ANCHORAGE AND BOND BEHAVIOR OF SMOOTHSURFACED NITINOL-SMA REBARS
F3-234
The anchorage and bond behavior of smooth-surfaced Shape Memory Alloys (SMAs) is investigated in this thesis, but specifically, the focus will be on Nitinol (Ni-Ti). Nitinol has distinctive properties, including Superelasticity Effect (SE) and Shape Memory Effects (SME). These properties make Nitinol bars suitable for civil and seismic engineering applications that require resilience and durability. However, Nitinol rebars possess a smooth surface, making it difficult to achieve adequate bonding and anchorage, potentially altering their load-carrying abilities. This inadequate anchorage and bonding restrict their use in the field of structural and seismic engineering. The main aim of this study is to investigate the anchorage mechanism and bond behavior of smooth-surfaced Nitinol bars embedded into concrete with emphasis on optimization of the performance of the two proposed anchorage systems. The experimental program is divided into two phases (Phase I and Phase II), where Phase II is dependent on the results of Phase I. Phase I experimentally evaluates the efficiency of two feasible wedge-type anchorage systems, Wedge-and-barrel (WB) and Spring anchor (SA), which are typically utilized in post-tensioning applications, and assesses their capabilities of anchoring smooth-surfaced Nitinol SMA rebars. A monotonic tensile testing regime consisting of 24 unique configurations was performed at different maximum strain levels (6%, 8%, and 10%) and loading rates (0.5, 2, 5, and 10 mm/min). The findings validate that the two anchorage systems illustrated consistent superelastic stress-strain responses. Significant performance differences were observed, wedge-and-barrel anchorage system showed increased stress capacity, improved load-transfer efficiency, and consistency across replicated tests, which can be attributed to its greater mechanical confinement and frictional interlock. The wedge-and-barrel anchorage system exhibits an increase of approximately 25% stress capacity compared to the spring anchorage system. On the other hand, the spring anchorage system exhibited good anchorage performance, with a slightly lower stress response and greater variation at higher levels of deformation due to the spring's compression mechanism. Phase II, a Taguchi-based optimization approach is experimentally applied to evaluate the bond behavior of smooth-surfaced Nitinol SMA rebars embedded in concrete. Five key parameters were considered: concrete cover (85, 90, 95, and 100 mm), concrete compressive strength (25, 40, 55, and 70 MPa), embedment length (100, 125, 150, and 175 mm), surface coating (smooth/none, rough epoxy, 300-μm sand coating, and 600-μm sand coating), and anchorage type (none, epoxybased anchor, spring anchor and wedge-and-barrel anchor). A L16 Taguchi orthogonal array was utilized to define 16 distinct specimen configurations, each configuration replicated three times to ensure reliability in the experimental results. Direct pull-out tests were conducted to evaluate bond strength, stress–slip response, and failure modes. An analysis of variance (ANOVA) was conducted, indicating that the anchorage type is the dominant parameter affecting the bond behavior of SMA, with a contribution of 83%. The wedge-and-barrel anchorage system has been found to be the optimum anchorage system among other systems under consideration, reaching a maximum bond stress of 6.334 MPa at a maximum slippage value of 2.03 mm. The Taguchi signal-to-noise analysis enabled the identification of which parameters have the most significant impact and which level combination yields the highest bond capacity. A predictive model was developed using the Taguchi approach. It was proven reliable, as the predicted optimal and additional specimens' bond response agreed with the experimental results, showing a maximum error of 10.3% across all specimens.
The outcomes of the experimental testing will give significant information on applying the smooth-surfaced Nitinol bars in the concrete and steel structures, which will contribute to the knowledge of their anchorage behavior. These results provide a base for further research in the field of optimizing Nitinol reinforcement in structural and seismic projects.