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This thesis examines the effects of reinforcement ductility on the strength and ductility of reinforced concrete slabs. An extensive experimental program examining the ultimate strength, ductility and failure mode of one-way and two-way reinforced concrete slabs is described and the results are presented and analysed. A numerical finite element model is developed and calibrated using the experimental data. The model is described and shown to accurately simulate the collapse load behaviour of reinforced concrete slabs containing reinforcement of any ductility class, including Class L welded wire fabric. Parametric studies using the numerical model to assess the effects of reinforcement ductility on structural behaviour are also presented and recommendations are made on the minimum reinforcement ductility levels appropriate for use in suspended slabs. The experimental and numerical tests investigated slabs with different types of boundary conditions (simply supported and continuous one-way slabs, corner-supported single panel two slabs and edge-supported two-way slabs), support settlement, steel reinforcement ratio, steel uniform elongation (su), steel ultimate to yield stress ratio (fsu/fsy) and rectangularity aspect ratio in the two-way slabs. In total, thirty one slabs were tested. The one-way slabs included four simply supported slabs, seven continuous slabs, and five continuous slabs with support settlement. The two-way slabs included eleven square and rectangular corner-supported slabs and four rectangular edge-supported slabs. The one-way simply-supported slabs were 850mm in width, 100mm in depth and 2,500mm in length. The continuous one-way slabs were 850mm in width, 100mm in depth and 4,350mm in length. The continuous one-way slabs and subjected to support settlement were 850mm in width, 120mm in depth and 6,300mm in length. The square two-way slabs had an edge length of 2,400mm and a depth of 100mm and the rectangular two-way slabs had width of 2,400mm, a length of 3,600mm and a depth of 100mm.

This thesis examines the effects of reinforcement ductility on the strength and ductility of reinforced concrete slabs. An extensive experimental program examining the ultimate strength, ductility and failure mode of one-way and two-way reinforced concrete slabs is described and the results are presented and analysed. A numerical finite element model is developed and calibrated using the experimental data. The model is described and shown to accurately simulate the collapse load behaviour of reinforced concrete slabs containing reinforcement of any ductility class, including Class L welded wire fabric. Parametric studies using the numerical model to assess the effects of reinforcement ductility on structural behaviour are also presented and recommendations are made on the minimum reinforcement ductility levels appropriate for use in suspended slabs. The experimental and numerical tests investigated slabs with different types of boundary conditions (simply supported and continuous one-way slabs, corner-supported single panel two slabs and edge-supported two-way slabs), support settlement, steel reinforcement ratio, steel uniform elongation (su), steel ultimate to yield stress ratio (fsu/fsy) and rectangularity aspect ratio in the two-way slabs. In total, thirty one slabs were tested. The one-way slabs included four simply supported slabs, seven continuous slabs, and five continuous slabs with support settlement. The two-way slabs included eleven square and rectangular corner-supported slabs and four rectangular edge-supported slabs. The one-way simply-supported slabs were 850mm in width, 100mm in depth and 2,500mm in length. The continuous one-way slabs were 850mm in width, 100mm in depth and 4,350mm in length. The continuous one-way slabs and subjected to support settlement were 850mm in width, 120mm in depth and 6,300mm in length. The square two-way slabs had an edge length of 2,400mm and a depth of 100mm and the rectangular two-way slabs had width of 2,400mm, a length of 3,600mm and a depth of 100mm.

Master of Science / Civil Engineering / Dunja Peric / The conventional triaxial test is the primary laboratory test for determining the shear strength of soils. Geotechnical field conditions such as long earth dams, long embankments, long retaining walls, strip foundations, tunnels, and buried pipelines often experience plane strain states of stress. However, stress strain and load deformation responses in plane strain loading differ considerably from responses observed in the conventional triaxial test. Research has shown that soils loaded in a plane strain state are far more sensitive to imperfections than soils tested in a conventional triaxial device. Plane strain loading leads to material instability manifested as sudden localized failure, resulting in decreased load-carrying capacity of the soil and compromised geotechnical and civil infrastructures. Although previous studies have mostly focused on granular materials, this research investigated the plane strain response of clay. An undrained plane strain compression test program was devised to investigate the effects of past stress history and strain rates on strain localization in kaolin clay. Experiments were carried out in a plane strain (or biaxial) device at Northwestern University, Evanston, Illinois. Because the device was heavily internally instrumented, strain localization progress was closely monitored throughout each biaxial test. Clay response in the biaxial test demonstrated three phases: (1) a homogenous response, (2) the onset and propagation of strain localization, and (3) the evolution of strain localization as a shear band. The duration of each phase was determined for each test, and a Lagrange strain tensor was used to obtain the evolution of volumetric and shear strains at the level of a shear band for three tests. Results revealed the development of large strains in these mesoscale structures. Furthermore, evolution of Mohr-Coulomb effective shear strength parameters was traced throughout the propagation and evolution phases by using two different methods. It showed that in clay samples, unlike in granular materials, the post-peak plateau, which is reached by deviatoric stress, corresponds to friction values that are significantly lower than the critical state values. Other researchers who used scanning electron microscope and anisotropy of magnetic susceptibility detected a significant reorientation of clay particles inside shear bands. Their findings combined with findings in this study lead to the conclusion that the sub-meso scale mechanism responsible for large shear strains and a severe reduction in effective friction is a significant reorientation of clay particles inside shear band.

AA7075 is a precipitation hardening structural aluminum alloy, which has garnered considerable interest in automotive industry, primarily due its lightweighting capacity compared to many other aluminum alloys from 2xxx and 6xxx series. However, the damage evolution in AA7075 is quite complex due to the presence of different second phase particles in the microstructure and their contribution on damage evolution is largely unknown at large plastic strains. The common second phase particles are η precipitates, θ precipitates and Fe-rich intermetallic particles. The current work presents an extensive multiscale numerical framework, which in conjunction with complementary experiments, is applied to study strain localization, void nucleation, growth, and coalescence in a particle rich matrix. Experimentally, void nucleation is observed to be driven by particle decohesion and particle fracture. Nanoscale molecular dynamics (MD) simulation is carried out to estimate interface properties of the three distinct particle types. The extracted properties are used as input for real particle field 2D and 3D microstructure based finite element (FE) models. The stochastic nature of particle fracture is described using a Weibull distribution, while the effect of grains is incorporated in terms of their Taylor factors. Ductile matrix is described using the well known Gurson Tvergaard Needleman (GTN) void damage model. Complementary experiments included uniaxial tensile tests carried out in-situ in Scanning Electron Microscope (SEM) and X-ray Computed Tomography (XCT), ex-situ high resolution XCT and Electron Back Scattered Diffraction (EBSD) tests. The FE models with three distinct particle stoichiometries and three competing damage mechanisms, show good agreement with experimental observations. Particle fracture marginally dominates particle decohesion. At low plastic strains, void nucleation is initiated by decohesion and fracture of larger Fe-rich particles, which facilitate formation of localized deformation bands. At large plastic strain, elevated stresses within the localized bands facilitate decohesion and fracture of more resistant η and θ precipitates. Due to their inherent larger size and more irregular morphology, θ precipitates contribute to voiding more than η precipitates. Under uniaxial tensile loads, void growth takes place in the middle of the specimen, driven by higher triaxiality stress state in the middle, relative to the surface. Void coalescence occurs along deformation bands driven by higher stresses due accumulated plastic strain within the bands, in a process known as void sheeting. / Thesis / Doctor of Philosophy (PhD)

I present physical shear-box experiments investigating the relationship between geometrical properties of shear zones and mechanical properties of deformed rocks. Experimental methodology is also examined critically and new materials for analogue modelling of shear localization are presented. First, I tested experimentally whether meaningful rheological information can be deduced from finite geometrical shear zone data. The results predict characteristic geometrical responses for certain end-member materials. However, it will be difficult to constrain such responses in the field. In the second part physical controls on deformation in the shear box are analysed for Newtonian and power-law fluids and an elastoviscoplastic strain-softening material. Since models always represent simplifications of the natural problem, it is essential to understand fully the physics of a given simulation. I show that displacement boundary conditions, model geometry, and rheology control shear zone geometry. Practical applications of the shear box for modelling natural shear localization and limitations of isothermal physical models with displacement boundary conditions in general are discussed. In the third part, new data on the rheology of highly-filled silicone polymers are introduced. Since dynamic similarity must be satisfied in analogue models to permit scaled, quantitative simulations of deformation processes, the choice of suitable rock analogues is critical for physical experiments. In particular, we address the problem of designing power-law fluids to model rocks deforming by dislocation creep. We found that highly-filled polymers have complex rheologies. Hence, such materials must be used with care in analogue modelling and only for certain experimental stress-strain rate conditions. Finally, I investigated whether fault network geometry and topography of brittle strike-slip faults are influenced by the degree of compaction of the host rock. Analogue shear experiments with loose and dense sand imply that the degree of sediment compaction may be a governing factor in the evolution of fault network structure and topography along strike-slip faults in sedimentary basins. Therefore, models of strike-slip faults should consider potential volume changes of deformed rocks.

In this thesis, I present field, microstructural, and Electron Backscatter Diffraction (EBSD) analyses of rock fabrics from high strain zones in exposures of lower crustal Cretaceous plutons at Breaksea Entrance, Fiordland, New Zealand. The interplay between deformation and metamorphism occurs across multiple scales at the root of a continental arc. I show a series of steps in which retrogressive metamorphism is linked to the accommodation of deformation. I define three main phases of deformation and metamorphism at Breaksea Entrance. The first phase (D1) involved emplacement of dioritic to gabbroic plutons at depths up to 60 km. The second phase (D2) is characterized by deformation and metamorphism at the granulite and eclogite facies that produced high strain zones with linear fabrics, isoclinal folding of igneous layering, and asymmetric pressure shadows around mafic aggregates. New structural analyses from Hāwea Island in Breaksea Entrance reveal the development of doubly plunging folds that define subdomes within larger, kilometer-scale gneiss domes. The development and intensification of S2 foliations within the domes was facilitated by the recrystallization of plagioclase and clinopyroxene at the micro-scale (subgrain rotation and grain boundary migration recrystallization), consistent with metamorphism at the granulite and eclogite facies and climb-accommodated dislocation creep. EBSD data show a strong crystallographic preferred orientation in plagioclase during D2 deformation. The third phase (D3) is characterized by deformation and metamorphism at the upper amphibolite facies that produced sets of discrete, narrow shear zones that wrap and encase lozenges of older fabrics. Structural analyses reveal a truncation and/or transposition relationship between the older S2 and the younger S3 foliations developed during D3. Progressive localization of deformation during cooling, hydration, and retrogression, resulted in the breakdown of garnet and pyroxene to form hornblende, biotite, fine plagioclase and quartz. EBSD data show a strong crystallographic preferred orientation in hornblende. During D3, hornblende and biotite accommodated most of the strain through fluid-assisted diffusion creep. The last two events (D2 and D3) reflect a transition in deformation and metamorphism during exhumation, as well as a focusing of strain and evolving strain localization mechanisms at the root of a continental arc. An examination of structures at multiple scales of observation reveals that fabrics seen in the field are a composite of multiple generations of deformation and metamorphism.

Geotechnical properties vary in space. Statistical parameters such as mean, deviation, and correlation length are characteristics for each sediment and formation history. The effects of spatial variability on the macro-scale mechanical properties of soils are investigated using Monte Carlo non-linear finite element simulations. Boundary conditions include 1) isotropic loading, 2) zero-lateral strain loading, 3) drained and undrained deviatoric loading, and 4) small-strain wave propagation. Emphasis is placed on identifying the effects of spatial variability on the stiffness and strength of soils, recognizing emergent phenomena, and creating the background for new geotechnical design methods that take into consideration spatial variability. The arithmetic mean of soil properties cannot be used to estimate the stiffness or strength of heterogeneous soils. Greater deviation and longer relative correlation length in the spatial distribution of soil properties yield a softer and weaker mechanical response. Load transfer concentrates along stiffer zones, leading to stress-focusing and lower K0 values. Drained loading promotes internal homogenization. Undrained deviatoric loading can cause percolation of internal weakness and shear strain localization. Spatial heterogeneity adds complexity to elastic wave propagation. Heterogeneous soil mixtures can be engineered to attain unique macroscale behavior

I present physical shear-box experiments investigating the relationship between geometrical properties of shear zones and mechanical properties of deformed rocks. Experimental methodology is also examined critically and new materials for analogue modelling of shear localization are presented. First, I tested experimentally whether meaningful rheological information can be deduced from finite geometrical shear zone data. The results predict characteristic geometrical responses for certain end-member materials. However, it will be difficult to constrain such responses in the field. In the second part physical controls on deformation in the shear box are analysed for Newtonian and power-law fluids and an elastoviscoplastic strain-softening material. Since models always represent simplifications of the natural problem, it is essential to understand fully the physics of a given simulation. I show that displacement boundary conditions, model geometry, and rheology control shear zone geometry. Practical applications of the shear box for modelling natural shear localization and limitations of isothermal physical models with displacement boundary conditions in general are discussed. In the third part, new data on the rheology of highly-filled silicone polymers are introduced. Since dynamic similarity must be satisfied in analogue models to permit scaled, quantitative simulations of deformation processes, the choice of suitable rock analogues is critical for physical experiments. In particular, we address the problem of designing power-law fluids to model rocks deforming by dislocation creep. We found that highly-filled polymers have complex rheologies. Hence, such materials must be used with care in analogue modelling and only for certain experimental stress-strain rate conditions. Finally, I investigated whether fault network geometry and topography of brittle strike-slip faults are influenced by the degree of compaction of the host rock. Analogue shear experiments with loose and dense sand imply that the degree of sediment compaction may be a governing factor in the evolution of fault network structure and topography along strike-slip faults in sedimentary basins. Therefore, models of strike-slip faults should consider potential volume changes of deformed rocks.

Thesis advisor: Seth C. Kruckenberg / In the earth’s lithosphere there exists both homogeneous and heterogeneous deformation on a variety of scales. The lower crust specifically plays a critical role in lithospheric deformation; however, the lower crust does not deform homogenously but rather heterogeneously in space and time. One of the best avenues for addressing heterogeneous lower crustal deformation is through an integrated study of shear zones. While many studies have identified factors such as strain rate and temperature as key actors in lower crustal strain localization, more studies are needed to characterize the dominant grain-scale mechanisms that accommodate the development of lower crustal shear zones. The primary aim of this research is to investigate the dominant mechanisms that lead to strain localization in the lower crust. The Capricorn Ridge Shear Zone (CRSZ), Central Australia, is an ideal location for study because it is a lower crustal shear zone that contains discrete zones of strain localization, primarily adjacent to major lithological boundaries. Previous studies conclude that competency contrast caused strain to localize at the lithologic boundaries of the CRSZ, a hypothesis that is tested in this study. Using microstructural, textural, and rheologic analysis, as well as field-based mapping and grain size piezometry, this study finds that differential stresses in Capricorn Ridge range from 17-27 MPa for quartz, 31-42 MPa for plagioclase, and 2.8-7.6 MPa for enstatite. Monophase aggregate strain rates range from 1.6 x 10-15 to 1.7 x 10-14 s-1 for quartz, 4.5 x 10-15 to 3.3 x 10-14 s-1 for plagioclase, and 6.0 x 10-20 to 1.2 x 10-18 s-1 for enstatite; corresponding effective viscosities 0.3-1.7 x 1021 Pa.s, 0.3-1.5 x 1021 Pa.s, and 0.2-1.8 x 1025 Pa.s for quartz, plagioclase, and enstatite, respectively. Data across the CRSZ show that while strain rate (viscosity) in monophase aggregates of quartz and plagioclase are generally similar across the shear zone, they do decrease at lithologic boundaries. In contrast to a previous study’s finding that competency contrast caused strain to localize at these boundaries, both quartz and plagioclase appear to record strain accumulation through grain size reduction. However, the observations made in previous studies are not negated by this study, as it is possible that grain size reduction in the mylonite zones near the boundaries caused strain to accumulate over time and therefore produce the observed pattern of increasing fabric intensity with proximity to the lithologic boundaries. / Thesis (MS) — Boston College, 2021. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.