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Osteoarthritis (OA) is a chronic, painful, and currently incurable disease characterized by structural deterioration and loss of function of synovial joints. OA is known to involve profound changes in bone density and microstructure near to, and even distal to, the joint. The prevailing view is that these changes in density and microstructure serve to stiffen the subchondral region thereby altering the mechanical environment (stresses and strains) within the epiphyseal and metaphyseal bone, and that these alterations trigger the aberrant cellular signaling and tissue damage characteristic of the progression of OA. Critically, however, these alterations in mechanical environment have never been well documented in a quantitative fashion in hip OA. Separately, although OA is generally thought to be inversely associated with fragility fracture, recent data challenge this idea and suggest that OA may actually modulate which regions of the proximal femur are at risk of fracture. Therefore, the goal of this work was to provide a spatial assessment of bone density and microstructure in hip OA and then examine the mechanical consequences of these OA-related abnormalities throughout the proximal femur. First, micro-computed tomography and data-driven computational anatomy were used to examine 3-D maps of the distribution of bone density and microstructure in human femoral neck samples with increasing severity of radiographic OA, providing evidence of the heterogeneous and multi-faceted changes in hip OA and discussion of the implications for OA progression and fracture risk. Second, the feasibility of proton density-weighted MRI in image-based finite element (FE) modeling, to examine stress, strain, and risk of failure in the proximal femur under sideways fall, was assessed by comparison to the current standard of CT-based FE modeling. Third, phantom-less calibration for CT-based FE modeling was used with clinically available pre-operative patient scans to assess bone strength and failure risk of the proximal femur in hip OA. Overall, the results of this work provide a rich, quantitative definition of the ways in which the bone mechanical environment under traumatic loading differ in association with hip OA, and then highlight the potential for clinical image-based FE methods to be used opportunistically to assess bone strength and failure risk at the hip. This work is significant because it directly tests the long-standing premise that OA is associated with changes in the mechanical environment of the bone tissue in ways that are impactful for OA progression; further, this work examines how these changes may influence risk of hip fracture. The results can be used to identify mechanistic predictors of OA progression, to inform development of bone-targeting treatments for OA, and to more broadly understand bone damage and fracture in this population.

A series of full-scale beam-to-column moment connection tests were completed to determine the effects of powder actuated fasteners (PAF) and puddle welds on the seismic behavior of steel moment connections.  In seismic regions, PAF are currently prohibited in the connection region (referred to as the protected zone) due to the concern of low-cycle fatigue fracture.  There is almost no information available in the literature regarding the seismic behavior of moment connections with PAF or puddle welds. Full-scale connection testing is the most accurate way to investigate the behavior of different moment connections with common defects and fasteners applied in the protected zone.  However, it is cost prohibitive to conduct full-scale testing programs that are sufficiently comprehensive to investigate a wide range of defect types, severity, and locations.  For this reason, it is desired to develop alternative methods of investigation.  A finite element (FE) model capable of simulating both the global deformation patterns and local buckling effects in a moment connection has been developed.  Validated FE models will allow for further evaluation through numerical simulation of additional configurations.  Furthermore, alternate, more economical, test configurations to experimentally investigate the effect of defects on steel moment connections were explored.  This report discusses the full-scale test setup, results and analysis of completed experimental testing, the development of an FE connection model, and the preliminary development of alternate test configurations. / Master of Science

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No description available.

The purpose of this research is to evaluate the influence of through-the-thickness reinforcements on the fracture behavior of stitched sandwich composites and to develop predictive methodologies to aid in simulating their damage-tolerant capability. Sandwich composites are widely used for their high stiffness-to-weight ratio due to their unique material architecture, which is composed of two rigid, outer facesheets that are bonded to a light-weight internal core. However, sandwich composites are limited by their low interlaminar strengths and can develop core-to-facesheet separation when subjected to low out-of-plane loads. In this study, sandwich composites were manufactured with through-the-thickness reinforcements, or stitches, to act as crack-growth inhibitors and to improve interlaminar properties. Stitch processing parameters, such as the number of stitches per unit area (stitch density) and stitch diameter (linear thread density), have considerable influence on the in-plane and out-of-plane behavior of composite structures. A design of experiments (DoE) approach is used to investigate stitch processing parameters and their interaction on the fracture behavior of stitched sandwich composites. Single cantilevered beam (SCB) tests are performed to estimate the required energy to propagate crack growth, or Mode I fracture energy, during the separation of the facesheet from the core. Additionally, embedded optical fibers within the SCB test articles are used to determine the internal crack front variation. During testing, unique fracture morphologies are obtained and show dependency on stitch processing parameters. Furthermore, embedded optical fibers indicate that the internal crack front is approximately 10% greater than visual edge measurements, which is primarily attributed to Poisson’s effect. The DoE approach is then used to develop a statistically informed response surface model (RSM) to optimize stitch processing parameters based on a maximum predicted fracture energy. Novel analytical formulations are developed for estimating the mode I fracture energy using the J-integral approach. The DoE approach is then used to inform and validate finite element models that simulate the facesheet-to-core separation using a discrete cohesive zone modeling approach. The predicted load and crack growth response show good agreement to experimental measurements and highlights the capability of stitching to arrest delamination in stitched sandwich composites.

Over the last few decades, evaluating the performance of existing structures has become increasingly important, particularly as the number of bridges reaching their design life continues to rise. As a result, there is a growing need for effective and accurate procedures to guide the assessment of the current structures' capacity and safety levels to implement appropriate maintenance and rehabilitation strategies. Evaluating a structure's performance involves assessing its ability to carry loads, resist external forces, and maintain its functionality over time. This is a complex process that requires a deep understanding of the structure's behavior, as well as knowledge of the environmental conditions it is subjected to. In recent years, technological advances and an increased understanding of reliability concepts have allowed for the development of more sophisticated tools and methods for structural evaluation. Thus, engineers and researchers can obtain more accurate and reliable data about a structure's performance, which can inform decision-making processes related to maintenance, repair, and replacement. This study aims to present a methodology that guides the assessment of existing structures' performance effectively and accurately. Precisely, the performance is measured in terms of redundancy and robustness. Thus, a comparison of existing reliability- and risk-based indicators is performed through an example application presented in one of the appended papers. The comparison allows an overview of the difference between the available measures and the type of information provided by each one of them. Also, in one of the appended papers a new algorithm for evaluating the failure probability value is proposed. The algorithm is based on metamodel strategies and integrates the advantages of kriging, learning, and copula functions. The proposed algorithm aims to reduce the number of performance function evaluations, so the number of model runs is feasible when using Finite Element Modeling (FEM). By comparing the available redundancy and robustness indicators, it was possible to observe that each measure provides different insights into these two structural properties. Additionally, direct comparison between them is challenging since their units can differ, and the lack of a target or standard values makes their interpretation difficult. Therefore, when using a specific indicator, it is required to specify the definition adopted clearly. Furthermore, the proposed algorithm showed through the validation examples and the case study that it can obtain the failure probability accurately and effectively. Its application resulted in a more economical methodology, in terms of computational cost, compared to other existing reliability methods.

Factors affecting the risk of ribcage injury in adult subjects during CPR were investigated using the torso region of the THUMS model, a full human body FE-model, representing an average adult male. The thoracic dynamic response of the model was compared to experimental PMHS hub loading impact data and live-subject CPR data found in the literature. The model was then used to study the risk of obtaining injuries in various simulated CPR conditions, also varying the stiffness of the costal cartilage. Parameters that are known to predict induced injuries were extracted from the model simulations, i.e. chest deflections, and maximum 1st principal strain and von-Mises stress in the ribs and sternum, as well as the pressure in the heart muscle. These were compared with values that have been reported to have the potential to cause injury. The predictions were compared to experimental findings of the probability of CPR resulting in fractures of the ribs and sternum. The previously mentioned parameters did not reach high enough values to predict fracture occurrences, but interesting trends were highlighted with regards to the different loading conditions investigated. It was demonstrated that human body FE-model simulation studies can be useful for investigating the influence of different CPR related loading conditions on the risk of occurrences of rib and sternal fractures.

The research and application of Ultra-high Performance Concrete (UHPC) has been developed significantly within the last 1-2 decades. Due to the specific property of high strength capacity, it is potential to be used in bridge deck system without shear reinforcement so that it provides even lighter self-weight of the deck. However, one of the shear component, dowel action, has not been adequately investigated in the past. In this dissertation, a particular test was designed and carried out to fully investigate the dowel action response, especially its contribution to shear resistance. In addition, research on serviceability and fatigue behaviors were expanded as well to delete the concern on other factors that may influence the application to the deck system. Both experimental and analytical methods including finite element modeling, OpenSees modeling and other extension studies were presented throughout the entire dissertation where required.

Woven structures are steadily emerging as excellent reinforcing components in dualphase composite materials subjected to multiaxial loads, thermal shock, and aggressive reactants in the environment. Metallic woven wire mesh materials display good ductility and relatively high specific strength and specific resilience. While use of this class of materials is rapidly expanding, significant gaps in mechanical behavior classification remain. This thesis works to address the mechanics of material knowledge gap that exists for characterizing the behavior of a metallic woven structure, composed of stainless steel wires on the order of 25 microns in diameter, and subjected to various loading conditions and stress risers. Uniaxial and biaxial tensile experiments, employing Digital Image Correlation (DIC) as a strain measurement tool, are conducted on woven wire mesh specimens incised in various material orientations, and with various notch geometries. Experimental results, supported by an ample analytic modeling effort, indicate that an orthotropic elastic constitutive model is reasonably capable of governing the macro-scale elasticity of the subject material. Also, the Stress Concentration Factor (SCF) associated with various notch geometries is documented experimentally and analytically, and it is shown that the degree of stress concentration is dependent on both notch and material orientation. The Finite Element Method (FEM) is employed on the macro-scale to expand the experimental test matrix, and to judge the effects of a homogenization assumption when modeling metallic woven structures. Additionally, plasticity of the stainless steel woven wire mesh is considered through experimental determination of the yield surface, and a thorough analytic modeling effort resulting in a modified form of the Hill yield criterion. Finally, mesoscale plasticity of the woven structure is considered, and the form of a multi-scale failure criterion is proposed and exercised numerically.