The formation of plastic strains in non-cohesive soils due to large number of loading cycles is a phenomenon of great importance in geotechnical and civil engineering. It constitutes a considerable cause for failures and deformations in various types of engineering applications including pavements. Strain accumulation due to cyclic loading has been studied for years through different models. This thesis reviews various models and focuses on the Bochum model through which, the most contributing soil and traffic parameters on permanent strains formation in pavement subgrades can be figured out. This represents the base for studying the serviceability of increasing the gross weights of vehicles that affect the behavior and size of cyclic loading. This was discussed through investigating the efficacy of increasing the number of vehicle axles and through increasing the vehicle gross weight while keeping the number of axles to check their impacts at the levels of strain formation in soil and consequently on its deformation. The results showed a considerable difference in settlements after changing the axle configurations of vehicles through increasing its number of axles. The work is expected to open a new area of scientific research in pavement designs seeking for ideal configurations of vehicle axles and to provide an advanced approach for studying soil deformations due to higher cyclic loadings.

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This thesis presents the results of testing and modeling conducted to characterize the performance of 3M™ VHB™ structural glazing tape in both shear and tension. Creep rupture testing results provided the failure time at a given static load and temperature, and ramp-to-fail testing results provided the ultimate load resistance at a given rate of strain and temperature. Parallel testing was conducted on three structural silicone sealants to compare performance. Using the time temperature superposition principle, master curves of VHB tape storage and loss moduli in shear and tension were developed with data from a dynamic mechanical analyzer (DMA). The thermal shift factors obtained from these constitutive tests were successfully applied to the creep rupture and ramp-to-fail data collected at 23°C, 40°C, and 60°C (73°F, 104°F, and 140°F), resulting in master curves of ramp-to-fail strength and creep rupture durability in shear and tension. A simple linear damage accumulation model was then proposed to examine the accumulation of wind damage if VHB tape is used to attach curtain wall glazing panels to building facades. The purpose of the model was to investigate the magnitude of damage resulting from the accumulation of sustained wind speeds that are less than the peak design wind speed. The model used the equation derived from tensile creep rupture testing, extrapolated into the range of stresses that would typically be generated by wind loading. This equation was applied to each individual entry in the data files of several real wind speed histories, and the fractions of life used at each entry were combined into a total percentage of life used. Although the model did not provide evidence that the established design procedure is unsafe, it suggested that the accumulation of damage from wind speeds below the peak wind speed could cause a VHB tape mode of failure that merits examination along with the more traditional peak wind speed design procedure currently recommended by the vendor. / Master of Science

Arid and semi-arid rangelands are important ecosystems that are consistently degraded through disturbances such as wildfires. After such disturbances, the invasion and dominance of annual grasses, like cheatgrass (Bromus tectorum L.), can lead to an overall loss of ecosystem productivity and an increase in fire frequency. To reduce weed dominance, native and introduced perennials species are typically be seeded in the fall. High mortality is seen from these seeded plant communities due to germinated seed being exposed to freezing, drought, fungal pathogens, and other biotic and abiotic stressors during winter months. We utilized wet-thermal accumulation models to first further validate the theory that germination from seeded plant populations occurs during periods of high environmental stress, and then to establish the practicality of abscisic acid seed coatings as a technology that could circumvent winter germination and mortality. In Chapter 1, we developed an excel workbook called Auto-Germ using Visual Basic for Applications, which allows users to estimate field germination timing based on wet-thermal accumulation models and field data. We then used Auto-Germ to model seed germination timing for 10 different species, across 6 years, and 10 Artemisia-steppe sites in the Great Basin of North America. We estimated that for the majority of the species analyzed, a mid to late-winter planting was required on average for the majority of the population to germinate in the spring. This planting time would be logistically difficult for many land managers, due to freezing and/or saturated soil conditions. In Chapter 2, we utilized wet-thermal accumulation models to evaluate the use of abscisic acid (ABA) to delay germination of Pseudoroegneria spicata (Pursh) Á. Löve (perennial native bunchgrass) across 4 years and 6 Artemisia-steppe sites. Germination models estimated that ABA seed treatments typically would delay germination of fall sown seed to late winter or early spring when conditions may be more favorable for plant establishment. Based on these results, we recommend both the use of wetthermal accumulation models as a tool in educating researchers and land managers in knowing when seeding practices should occur, and the further study of ABA seed coatings as a technology that may improve plant establishment of fall sown seeds.