The structural damage after the Christchurch earthquake (2011) led to extensively damaged facilities that did not collapse but did require demolition, representing more than 70% of the building stock in the central business district. These severe economic losses that result from conventional seismic design clearly show the importance of moving towards resilience-based design approaches of structures. For instance, special reinforced masonry shear walls (SRMWs), which are fixed-base walls, are typically designed to dissipate energy through the yielding of bonded reinforcement while special detailing is maintained to fulfill ductility requirements. This comes at the expense of accepting residual drifts and permanent damage in potential plastic hinge zones. This design process hinders the overall resilience of such walls because of the costs and time associated with the loss of operation and service shutdown. In controlled rocking systems, an elastic gap opening mechanism (i.e., rocking joint) replaces the typical yielding of the main reinforcement in conventional fixed-base walls, hence reducing wall lateral stiffness without excessive yielding damage. Consequently, controlled rocking wall systems with limited damage and self-centering behavior under the control of unbonded post-tensioning (PT) are considered favorable for modern resilient cities because of the costs associated with service shutdown (i.e., for structural repairs or replacement) are minimized. However, the difficulty of PT implementation during construction is challenging in practical masonry applications. In addition, PT losses due to PT yielding and early strength degradation of masonry reduce the self-centering ability of controlled rocking masonry walls with unbonded post-tensioning (PT-CRMWs). Such challenges demonstrate the importance of considering an alternative source of self-centering. In this regard, the current study initially evaluates the seismic performance of PT-CRMWs compared to SRMWs. Next, a new controlled rocking system for masonry walls is proposed, namely Energy Dissipation-Controlled Rocking Masonry Walls (ED-CRMWs), which are designed to self-center through vertical gravity loads only, without the use of PT tendons. To control the rocking response, supplemental energy dissipation (ED) devices are included. This proposed system is evaluated experimentally in two phases. In Phase I of the experimental program, the focus is to ensure that the intended behavior of ED-CRMWs is achieved. This is followed by design guidance, validated through collapse risk analysis of a series of 20 ED-CRMW archetypes. Finally, Phase II of the experimental program evaluates a more resilient ED-CRMW is evaluated, which incorporates a readily replaceable externally mounted flexural arm ED device. Design guidance is also provided for ED-CRMWs incorporating such devices. / Thesis / Doctor of Philosophy (PhD)

Thermosyphon transient operation was numerically modeled. The numerical model presented in this work overcame the limitations of previous studies by including transient conduction in the vessel wall, shear stress between the rising vapor and the falling film in the thermosyphon, the influence of the mass in the liquid pool in the evaporator, and by using a more refined and accurate numerical grid. Unique to this model was the accounting for temporal changes in the effective length of the vapor space due to the expanding and contracting of non-condensable gases in the vapor space. The model assumed quasi-steady one-dimensional vapor flow, transient one-dimensional flow in the falling liquid film, and transient behavior in the liquid pool in the evaporator. The model also assumed transient two-dimensional conduction in the thermosyphon wall. Using fundamental principles, the governing equations used in the numerical model were developed and then written in finite difference form. The finite difference forms of the governing equations were integrated using an explicit scheme. A sensitivity study was performed and found that the numerical model was accurate to 4%. An experiment was also conducted to validate the numerical model. The experiment used three distinct transient heat loads to simulate gradual, moderate and sharp increases in temperature. The uncertainty of the experiment was shown to be 2.3%. The temperatures from the numerical model were then compared to those measured during the physical experiment to determine the validity of the numerical model. The model was further exercised to develop a useful engineering relationship that can be used to predict the transient performance of a thermosyphon.

The performance of a coupled viscoplastic model of FSW has been evaluated over a variety of tool RPMs and feed rates. Initial results suggested that further optimization of the material parameters and an additional ability to model the thermal recovery of the material would improve the overall performance of the model. Therefore, an experimental/numeric approach was taken to improve and quantitatively compare the performance of the model based upon the thermal profile of the workpiece. First, an experimental method for obtaining real-time temperature measurements during Friction Stir Processing (FSP) of 304L Stainless Steel was developed. The focus of the method was to ensure that the obtained temperatures were both accurate and repeatable. The method was then used to obtain thermal cycle data from nine welds, each at different operating conditions ranging in tool rotational speed from 300 to 500 RPMs and in feed rate from 0.85 to 2.54 mm/s (2 - 6 in/min). Then a family of nine numerical models was created, each model corresponding to one welding condition. The performance due to improved convergence stability and the added thermal recovery term are also discussed. A gradient following technique was used to optimization and iteratively adjust nine material parameters to minimize the difference between the numerical and experimental temperature for the whole family of models. The optimization decreased the squared error between the numerical and measured temperatures by 76%. Recommendations are also made that may allow the optimization method to return greater dividends.

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The feasibility of using ground improvement at existing highway bridges to mitigate the risk of earthquake-induced liquefaction damage has been studied. The factors and phenomena governing the performance of the improved ground were identified and clarified. Potential analytical methods for predicting the treated ground performance were investigated and tested. Key factors affecting improved ground performance are the type, size, and location of the treated ground. The improved ground behavior is influenced by excess pore water pressure migration, ground motion amplification, inertial force phasing, dynamic component of liquefied soil pressure, presence of a supported structure, and lateral spreading forces. Simplified, uncoupled analytical methods were unable to predict the final performance of an improved ground zone and supported structure, but provided useful insights. Pseudostatic stability and deformation analyses can not successfully predict the final performance because of their inability to adequately account for the transient response. Equivalent-linear dynamic response analyses indicate that significant shear strains, pore water pressures and accelerations will develop in the improved ground when the treated-untreated soil system approaches resonance during shaking. Transient seepage analyses indicate that evaluating pore pressure migration into a three-dimensional improved zone using two-dimensional analyses can underestimate the pore pressures in the zone. More comprehensive, partially-coupled analyses performed using the finite difference computer program FLAC provided better predictions of treated ground performance. These two-dimensional, dynamic analyses based on effective stresses incorporated pore pressure generation, non-linear stress-strain behavior, strength reduction, and groundwater flow. Permanent movements of structures and improved soil zones were predicted within a factor of approximately two. Predictions of ground accelerations and pore water pressures were less accurate. Dynamic analyses were performed with FLAC for an example bridge pier and stub abutment on an approach embankment supported on shallow foundations and underlain by thick, liquefiable soils with and without improved ground zones. Ground improvement that restricted movements of the pier and stub abutment to tolerable levels included improved zones of limited size extending completely through the underlying liquefiable soils and formed through densification by compaction grouting or cementation by chemical grouting or jet grouting. A buttress fill at the abutment was unsuccessful. / Ph. D.

We develop a methodology for systematic inversion of quantitative stratigraphic models. Quantitative stratigraphic modeling predicts stratigraphy using numerical simulations of geologic processes. Stratigraphic inversion methodically searches the parameter space in order to detect models which best represent the observed stratigraphy. Model parameters include sea-level change, tectonic subsidence, sediment input rate, and transport coefficients. We successfully performed a fully automated process based stratigraphic inversion of a geologically complex synthetic model. Several one and two parameter inversions were used to investigate the coupling of process parameters. Source location and transport coefficient below base level indicated significant coupling, while the rest of the parameters showed only minimal coupling. The influence of different observable data on the inversion was also tested. The inversion results using misfit based on sparse, but time dependent sample points proved to be better than the misfit based on the final stratigraphy only, even when sampled densely. We tested several inversion schemes on the topography dataset obtained from the eXperimental EarthScape facility simulation. The clustering of model parameters in most of the inversion experiments showed the likelihood of obtaining a reasonable number of compatible models. We also observed the need for several different diffusion-coefficient parameterizations to emulate different erosional and depositional processes. The excellent result of the piecewise inversion, which used different parameterizations for different time intervals, demonstrate the need for development or incorporation of time-variant parameterizations of the diffusion coefficients. We also present new methods for applying boundary condition on simulation of diffusion processes using the finite-difference method. It is based on the straightforward idea that solutions at the boundaries are smooth. The new scheme achieves high accuracy when the initial conditions are non vanishing at the boundaries, a case which is poorly handled by previous methods. Along with the ease in implementation, the new method does not require any additional computation or memory. / Ph. D.

River-floodplain connectivity is the degree of water-driven transport of matter, energy, and organisms between rivers and their floodplains. Recent advancement of high-resolution lidar data and numerical modeling is helpful to explore river-floodplain connectivity precisely to improve our predictions of sediment transport and deposition on floodplains. In the present work, we studied floodplain sediment transport and deposition, and juvenile mussel settling in three river systems in the US. A two-dimensional hydrodynamic model was developed and simulated model results were coupled with field measurements to study river-floodplain systems of the East Fork White River in Indiana, South River in Virginia, and Dan River in North Carolina. Results show that the East Fork White River in Indiana is capable of supplying sand to the channels on the floodplain and these floodplain channels can transport sand in suspension and gravel as bedload. These floodplain channels are supply limited under the current hydrologic regime and identified as net erosional. On the South River floodplain in Virginia, incorporating hydrologic flowpaths as an explicit measure of river-floodplain connectivity can improve predictions of floodplain sediment deposition. Three regression models were developed incorporating flow pathways and the best model was applied to hydrodynamic model results to create a spatial map of floodplain sedimentation rate. The deposition map highlights how floodplain topography and river-floodplain connectivity affect sedimentation rates and can help inform the development of floodplain sediment budgets. Lastly, streamflow conditions were investigated in the Dan River, North Carolina as they affect juvenile freshwater mussel settling. Two uplooking velocity sensors on the river bed were deployed and hydraulic parameters were measured for a 7-mo period in May-November 2019 to estimate the juvenile mussel settling. Results show that juvenile freshwater mussels as large as 280-508 µm could always be suspended during our study period and not be able to settle onto the river bed at the location of our velocity sensors. Therefore, the flow and shear velocity during our study period was high enough to prohibit the recruitment of juvenile freshwater mussels from settling out of suspension at the sensor locations. Modest flow obstructions such as large boulders, downed trees, or large wood that create downstream wakes may be important features that provide suitable conditions for the settling of juvenile freshwater mussels onto the river bed. Furthermore, low flows have been increasing since the year 2000 which may be exacerbating the decline in freshwater mussel populations. / Doctor of Philosophy / Human civilization has developed near rivers due to the wide range of benefits provided by rivers. Rivers provide food, water, and energy to more than 2.7 billion people around the world. However, the health of the rivers is degrading rapidly to meet the increasing demand of the growing population. We studied water, sediment, and mussel transport in the three rivers in the US: East Fork White River in Indiana, South River in Virginia, and Dan River in North Carolina. These rivers play an important role in agriculture, water supply, sediment, and nutrient transport of the surrounding environment. Our research work on East Fork White River in Indiana, USA shows that the area directly adjacent to the river is eroding, which is important information for river managers and policymakers. As part of that work, we identified the potential of various sizes of sediment to move over this area at different flows and developed a method to predict the largest sediment size that could be moved in water and hopping along the ground. This method is also applicable to other areas along rivers and the coast. We estimated the sediment deposition rate, deposition volume, and prepared a spatial map of the sediment deposition pattern for the South River floodplain in Virginia. From this map, deposition hot spots could be identified. We estimated that 66% of the sediment deposited adjacent to the South River was located in 32% of the area. This information will be helpful for understanding how sediment and sediment-associated pollutants deposit around rivers. Our work on the Dan River in North Carolina was focused on freshwater mussels. Our results showed that juvenile freshwater mussels could not have settled onto the river bed at the location of our measurements. Historical data reveal that freshwater mussels are declining at an alarming rate in that river, posing a threat to the river environment. We identified that streamflow has been increasing over the last two decades, which could be a potential cause of declining freshwater mussels.

Sediment pulses are defined as large amounts of loose sediment that are suddenly deposited in river corridors due to the action of external factors or processes of natural or anthropogenic origin. Such factors and processes include landslides, debris flows from tributaries, volcanic eruptions, dam removal projects, and mining-related activities. Their occurrence is associated with a surplus in sediment load to downstream reaches, and therefore, with severe channel aggradation and degradation, significant floodplain deposition, increase in flood frequency, damage of infrastructure, and impairment of aquatic habitats. The main objective of this research is to develop a better understanding of the fundamental mechanisms that govern the propagation of these sediment-flow hazards in alluvial sand-bed rivers. Specifically, the study presented herein is divided into three separate parts to achieve this overarching goal. First, a component intended to improve the numerical modeling of morphodynamic processes in alluvial sand-bed rivers by proposing a novel solution methodology that applies either the decoupled or the coupled modeling approach based on local flow and sediment transport conditions. Secondly, a detailed numerical analysis to characterize the behavior of fine-grained sediment pulses (i.e. composed of granular material in the sand size range) in alluvial sand-bed rives by identifying the properties of these types of pulses, as well as the characteristics of riverine environments, that are most relevant to their downstream migration. And lastly, a case study application to assess the effect of the magnitude, duration, and frequency of severe hydrologic events on the overall propagation behavior of fine-grained sediment pulses in alluvial sand-bed rivers. Ultimately, this research aims to contribute towards reducing the uncertainty associated with the impact of these phenomena, and hence, improving the resilience of rivers corridors. / Ph. D.