Theses and Dissertations at Montana State University (MSU)
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Item In-plane shear behavior of geosynthetics from bias biaxial tests using digital image correlation(Montana State University - Bozeman, College of Engineering, 2019) Schultz, Emily Christine; Chairperson, Graduate Committee: Steven PerkinsGeosynthetics are polymeric membranes used for structural reinforcement of soils in a variety of roadway and foundation applications, many of which create biaxial loading on the geosynthetic. Orthotropic linear elastic models have been used to represent geosynthetic behavior at working load levels for engineering design purposes. Typically, the models rely on index parameters obtained from test methods that do not represent the biaxial field loading conditions. Proper calibration of these models requires load-strain data obtained from tests that have controlled stress and strain boundaries such as biaxial tension tests. Previously at Montana State University, Haselton (2018) successfully used a custom biaxial device to perform biaxial tension tests on cruciform shaped geosynthetic specimens, producing a partial set of resilient elastic constants for two woven geotextiles and six biaxial geogrids. To complete the set of elastic constants by determination of the in-plane shear modulus, another mode of loading was necessary. Literature from biaxial shear tests of architectural membranes suggested cutting the cruciform shaped samples with the principal material directions on a 45-degree bias, which causes the sample to shear when the cruciform axes are unequally loaded. This test mode was successfully implemented with the existing biaxial device to determine the resilient in-plane shear modulus using an orthotropic linear elastic model. Full-field strain measurements were captured using digital imaging correlation (DIC) software available at Montana State University. DIC was shown to produce equivalent strain measurements to the mechanical instrumentation (LVDTs) used by Haselton, enabling a combined dataset. The full-field DIC strain measurements were then used to validate Haselton's assumption regarding the region of uniform strain and to identify the region of uniform strain for data collection in this thesis. DIC also showed reasonably pure biaxial tension in the cruciform samples, validating the elastic constant derivations for both Haselton and this thesis.Item Experimental and analytical investigation of masonry infill and confined masonry wall assemblies(Montana State University - Bozeman, College of Engineering, 2017) Johnson, Maxim Gordon; Chairperson, Graduate Committee: Damon FickMasonry has the benefit of strength and ease of construction but lacks the ability to resist lateral forces due to its brittle nature. However, with the addition of concrete confining frames to plain masonry walls, additional strength and ductility can be attained. Two such confinement systems include masonry infill and confined masonry walls. Currently, masonry infill assemblies are the most common form of lateral force resisting systems in countries where access to more traditional concrete and steel materials is limited. However, recent studies have stated that confined masonry provides improved performance because of the bond between the concrete and brick. This thesis presents an investigation of the behavior of both types of concrete confinement methods and identifies advantages of each system with regards to strength, ductility, and performance during strong ground motion events. To accomplish this objective, 1/3-scale specimens were constructed and tested in direct shear to determine the load-displacement response for both masonry infill and confined masonry walls and compared with results of each type of concrete confinement technique as compared to a plain masonry specimen. The masonry infill wall strength was 35% larger and deflected ten times more than the plain masonry wall at peak load. The confined masonry showed 80% more strength capacity; however, only deflected 2.5 times more than the plain masonry wall at peak load. The test results were incorporated into analytical models that approximated the load displacement response observed during the tests. The models were used to perform a nonlinear push-over analysis on a reduced scale 5-story building damaged by the Nepal earthquake. The first story walls of the confined masonry model failed at a base shear that was 27% larger than the masonry infill model. First story drifts were 64% larger in the masonry infill model. This supports the general observation that each wall has merit in a specific design scenario. Masonry infill walls may be preferred in for designs where energy dissipation may be critical. On the strength side, confined masonry walls may be preferred where strength is preferred over ductility.Item Tentative shear design method for steel fiber reinforced concrete flat plates(Montana State University - Bozeman, College of Engineering, 1984) Ofili, Charles Afamefuna ChukwuemekaItem Nanocomposites : a study of theoretical micromechanical behavior using finite element analysis(Montana State University - Bozeman, College of Engineering, 2009) Milliren, Eric Carlton; Chairperson, Graduate Committee: Christopher H. M. JenkinsCurrent research in nanotechnology has produced an increasing number of possibilities for advanced materials. Among those materials with potential advanced mechanical properties are fiber-reinforced composite laminates that utilize nanoscale fiber diameters. Through a combination of studying classic micromechanical models and modern computer-aided finite element analysis (FEA), the advantages for utilizing these nanofibers in advanced structural applications, such as space mirror backings, was investigated. The approach for modeling these composite structures was that of a Representative Volume Element (RVE). Using the program ABAQUS/CAE, a RVE was created with the goals of accurately comparing to the shear lag theory, effectively incorporating "interphase" zones that bond the constituents, and demonstrating effects of down-scaling fiber diameter. In this thesis, the progression of the ABAQUS model is thoroughly covered as it developed into a verified model correlating with the shear lag theory. The model produced was capable of utilizing interphase if desired, and was capable of off-axis loading scenarios. A MathCAD program was written in order to employ the published theoretical techniques, which were then compared to the FEA results for verification. The FEA model was found to work well in conjunction with the theory explored using MathCAD, after which the nanofiber FEA model showed some clear advantages over a conventional-sized model, specifically an increase in strength of the composite RVE. Finally, it was determined that the interfacial bonding strength plays a large role in the structure of the interphase zone, and thus the overall strength of the composite.Item Effect of fiber diameter on stress transfer and interfacial damage in fiber reinforced composites(Montana State University - Bozeman, College of Engineering, 2011) Peterson, William Matthew; Chairperson, Graduate Committee: Christopher H. M. JenkinsIn this work, the effect of fiber diameter upon the strength, stiffness, and damage tolerance of a fiber-reinforced polymer composite laminate structure was investigated. Three cases were considered, in which the fiber diameters of 16, 8, and 4 microns were used. A fiber volume fraction of 32% was assumed in each model. Micromechanical, shear-lag, and progressive damage analyses were performed using finite element models of the structure, which was subjected to tensile loading in the fiber direction. Fiber-matrix load transfer efficiencies and the stress distributions near broken fibers within the composite structure were investigated and results compared for each fiber diameter. In addition, the effect of fiber diameter upon the initiation and evolution of fiber-matrix interfacial damage and debonding was studied using cohesive interface elements. For a specified volume fraction and load condition, as the fiber diameter was decreased the load transfer efficiency and effective stiffness of the broken fiber model increased. Also, as the fiber diameter was decreased, the initiation of damage at the fiber-matrix interface occurred at greater stresses and the subsequent growth of damage was less extensive. These results indicate that, for the same total mass, the performance and damage tolerance of composite materials may be enhanced simply by using smaller diameter fibers.