A computationally efficient multilevel decomposition and optimization framework is developed for application to automotive structures. A full scale finite element (FE) model of a passenger car along with a dummy and occupant restraint system (ORS) is used to analyze crashworthiness and occupant safety criteria in two crash scenarios. The vehicle and ORS models are incorporated into a decomposed multilevel framework and optimized with mass and occupant injury criteria as objectives. A surrogate modeling technique is used to approximate the computationally expensive nonlinear FE responses. A multilevel target matching optimization problem is formulated to obtain a design satisfying system level performance targets. A balance is sought between crashworthiness and structural rigidity while minimizing overall mass of the vehicle. Two separate design problems involving crash and crash+vibration are considered. A major finding of this study is that, it is possible to achieve greater weight savings by including dummy-based responses in optimization problem.

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No / Purpose: The immobilisation and restraint of children to facilitate radiographic examination is a controversial issue that has been relatively ignored by radiography research. The aim of this study was to begin to fill this gap by providing a description of restraint used in a limited number of clinical sites in order to highlight any perceived need for training, policies or guidelines in the use of child immobilisation and restraint. Methods: A cross-sectional survey design using a postal questionnaire was adopted. One hundred and sixty-seven questionnaires were distributed to radiographers employed within six hospital Trusts. Results: A response rate of 83.2% (n=139/167) was achieved. Ninety-three percent (93.5%, n=130/139) of respondents indicated that restraining techniques were used although only 19.2% (n=25/130) had received specific training in safe restraining techniques and 7.9% (n=11/139) in distraction techniques as an alternative to restraint. A need for further guidance and support for clinical staff was evident with 73.3% (n=74/101) of respondents identifying a need for specific guidelines and 84.6% (n=110/130) indicating that further training opportunities were required. Conclusions: The use of restraint in paediatric plain film radiography is an apparently widespread practice and support for clinical radiographers through the development of training opportunities and practice guidelines are seen as essential in order to promote high quality paediatric radiography practices.

This dissertation presents the results of a research effort aimed at improving the current occupant injury criteria typically used to assess occupant injury risk in crashes involving roadside hardware such as guardrail. These metrics attempt to derive the risk of injury based solely on the response of the vehicle during a collision event. The primary purpose of this research effort was to determine if real-world crash injury prediction could be improved by augmenting the current vehicle-based metrics with vehicle-specific structure and occupant restraint performance measures. Based on an analysis of the responses of 60 crash test dummies in full-scale crash tests, vehicle-based occupant risk criteria were not found to be an accurate measure of occupant risk and were unable to predict the variation in occupant risk for unbelted, belted, airbag only, or belt and airbag restrained occupants. Through the use of Event Data Recorder (EDR) data coupled with occupant injury data for 214 real-world crashes, age-adjusted injury risk curves were developed relating vehicle-based metrics to occupant injury in real-world frontal collisions. A comparison of these risk curves based on model fit statistics and an ROC curve analysis indicated that the more computationally intensive metrics that require knowledge of the entire crash pulse offer no statistically significant advantage over the simpler delta-V crash severity metric in discriminating between serious and non-serious occupant injury. This finding underscores the importance of developing an improved vehicle-based injury metric. Based on an analysis of 619 full-scale frontal crash tests, adjustments to delta-V that reflect the vehicle structure performance and occupant restraint performance are found to predict 4 times the variation of resultant occupant chest acceleration than delta-V alone. The combination of delta-V, ridedown efficiency, and the kinetic energy factor was found to provide the best prediction of the occupant chest kinematics. Real-world crash data was used to evaluate the developed modified delta-V metrics based on their ability to predict injury in real-world collisions. Although no statistically significant improvement in injury prediction was found, the modified models did show evidence of improvement over the traditional delta-V metric. / Ph. D.

Over the past fifty years, many states have recognized the benefits of making precast, prestressed multi-girder bridges continuous by connecting the girders with a continuity diaphragm. Although there is widespread agreement on the benefits of continuous construction, there has not been as much agreement on either the methods used for design of these systems or the details used for the continuity connections. To aid designers in choosing the most appropriate method, an analytical and experimental study was undertaken at Virginia Tech. Analyses were done to compare the differences in the predicted continuity moments for different design methods and assumptions over a range of commonly used systems of Precast Concrete Bulb Tee (PCBT) girders and cast-in-place slabs. The results of the analyses were used to develop three continuity connection details for testing during the experimental study. Three different continuity connections were tested using full depth PCBT 45 in. deep girders made continuous with a 6 ft wide slab. The bottom of the ends of the girders were made continuous with the continuity connection by extending prestressing strands for one test and extending 180 degree bent bars for the other test. Both connections adequately resisted service, cyclic, and ultimate loads. But, the test with the extended bars remained stiffer during cyclic loading and is recommended for use. A third test was performed on a system using only a slab cast across the top of the girders. Two primary cracks formed above the ends of the girders at the joint during service testing, after which no significant increase in damage took place. Results from the analytical study indicate that the predicted positive thermal restraint moments may be significant, similar in magnitude to the actual positive cracking moment capacities. Results from the experimental study indicate that restraint moments develop early due to thermal expansion of the deck during curing and subsequent differential shrinkage; however, the magnitudes of the early age restraint moments are much less than conventional analyses predict. / Ph. D.

The response of light-frame timber shear walls to lateral forces is the focus of the dissertation. The objective of this study was to obtain performance characteristics of shear walls with various aspect ratios and overturning restraint via experimental testing and analytical modeling. Presented are the test data of monotonic and cyclic tests on fifty-six light-frame timber shear walls with aspect ratios of 4:1, 2:1, 1:1, and 2:3. Overturning restraint conditions represent engineered construction and conventional construction practices. The walls representative of the engineered construction were attached to the base by means of tie-down anchors and shear bolts. As opposed to engineered construction, conventionally built walls were secured to the base by nails or shear bolts only. The specimens were tested in a horizontal position with oriented strandboard (OSB) sheathing on one side. To obtain conservative estimates, no dead load was applied in the wall plane during the tests. The nail-edge distance across the top and bottom plates varied from 10 mm (3/8 in.) to 19 mm (3/4 in.). Twelve walls were repaired after the initial tests and re-tested. A mechanics-based model was advanced to predict the racking resistance of conventional multi-panel shear walls using simple formulae. The deflections of engineered and conventional shear walls were predicted using the energy method combined with empirical formulae to account for load-deformation characteristics of sheathing-to-framing connections and overturning restraint. The proposed formulae were validated through comparison with test results obtained during this study. The results of the study serve to further development of a mechanics-based methodology for design of shear walls accounting for various wall configurations and boundary conditions. / Ph. D.

This research document focuses on prestressed PCBT girders made composite with a cast-in-place concrete deck and continuous over several spans through the use of continuity diaphragms. The current design procedure in AASHTO states that a continuity diaphragm is considered to be fully effective if a compressive stress develops in the bottom of the diaphragm when the superimposed permanent load, settlement, creep, shrinkage, 50 percent live load, and temperature gradient are summed, or if the girders are stored at least 90 days when continuity is established. It is more economical to store girders for fewer days, so it is important to know the minimum number of days that girders must be stored to satisfy AASHTO requirements. In 2005, Charles Newhouse developed the positive moment diaphragm reinforcement detail that is currently being adopted by VDOT. This thesis concludes that Newhouse's detail, four No. 6 bars bent 180° and extended into the diaphragm, is adequate for all girders except for the PCBT-77, PCBT-85, and the PCBT-93 when the girders are stored for a minimum of 90 days. It is recommended that two additional bent strands be extended into the continuity diaphragm for these three girder sizes. It was also concluded that about half of the cases result in a significant reduction in the minimum number of storage days if the designer is willing to perform a detailed analysis. The other half of the cases must be stored for 90 days because the total moment in the diaphragm will never become negative and satisfy the AASHTO requirement. In general, narrower girder spacing and higher concrete compressive strength results in shorter required storage duration. The PCA Method was used in this analysis with the updated AASHTO LRFD creep, shrinkage, and prestress loss models. A recommended quick check is to sum the thermal, composite dead load, and half of the live load restraint moments. The girder must be stored 90 days if that sum is positive, and a more detailed time-dependent analysis would result in a shorter than 90 day storage period if that sum is negative. / Master of Science

Objective: To investigate differences in dietary intake variables and anthropometric measurements in healthy young adult women of healthy body mass index (BMI) with high and low scores of cognitive eating restraint (CER), disinhibition (DI), and hunger. Design: Cross-sectional study in which the Eating Inventory was completed along with the Block Food Frequency Questionnaire and anthropometric measurements using standard procedures and dual-energy X-ray absorptiometry, respectively. Participants: 65 healthy young adult women. Setting: This research was conducted in the Bone Laboratory on the campus of the Virginia Polytechnic Institute and State University, Blacksburg, Virginia. Statistical analyses: Independent t-tests, Pearson correlation coefficient analyses, and general linear regression models. Results: Women with high CER scores (n=32; mean±SD CER score=13.1±2.4) consumed more fruits per day (2.4±0.9 svg/d) compared to women with low CER scores (n=33; CER score=4.5±3.0; fruits=1.8±1.1 svg/d; p<0.05). Women with high hunger scores (n=35; hunger score=7.5±2.2) consumed less fruits per day (1.8±0.9 svg/d) compared to women with low hunger scores (n=30; hunger score=3.0±1.1; fruits=2.4±1.1 svg/d; p<0.05). Women with high compared to low CER scores had higher body weight (p<0.05), BMI (p<0.05), fat mass (p<0.05), and body fat percentage (p<0.05), while women with high (n=31; DI score=7.6±2.5) compared to low (n=34; DI score=2.9±1.0) DI scores were taller (p<0.05). Hunger predicted estimated daily dietary intakes of total energy (p<0.05), protein (p<0.01), and fat (p<0.01), while CER (p<0.05) and DI (p<0.05) predicted estimated daily dietary fruit intake. Conclusion: In healthy young adult women, eating characteristics can distinguish between some dietary intake patterns and anthropometric measurements. Hunger is a predictor of estimated energy, protein, and fat intake in these women. / Master of Science

Written for the Institute of Air and Space Law. Title from title page of PDF (viewed 2010/04/14). Includes bibliographical references.

abstract: Long-term results of dietary weight loss interventions are not promising, with rates of weight loss maintenance at a mere 20%. Psychological factors related to weight maintenance include setting unrealistic weight goals, poor problem-solving skills, low self-efficacy, dichotomous thinking, and external locus of control. The ability to maintain a stable bodyweight over time has been associated with optimal health outcomes, lower stress levels, and higher general well-being. Dichotomous thinking has been associated with overeating and increased bodyweight. Cognitive restraint, disinhibition, and hunger are three dimensions of human eating behavior that appear to be important to understanding weight loss maintenance. Individuals who attempt to maintain their bodyweight via dietary restraint mechanisms are more susceptible to excessive eating episodes. Disinhibition has been found to be the strongest predictor of weight gain, while the research on the association between hunger and bodyweight is mixed. This study sought to evaluate the relationship between dichotomous thinking toward food and various eating behaviors (binge eating, cognitive restraint, disinhibition, and hunger). A multiple regression analysis revealed that binge eating, cognitive restraint, disinhibition, and hunger were each significant unique predictors of higher body mass index (BMI). Higher levels of hunger predicted lower BMI, controlling for cognitive restraint, disinhibition, and binge eating. Mediation analyses revealed that dichotomous thinking mediated the relationships between binge eating and BMI, cognitive restraint and BMI, and disinhibition and BMI. Further analysis revealed that binge eating mediated the relationship between dichotomous thinking and BMI, indicating that thinking of food in black-and-white could lead to higher rates of binge eating, and the excess calorie consumption could lead to increased BMI. The study findings suggest that a strong focus should be made to promote a more flexible attitude toward food in an effort to improve weight loss maintenance in the population. / Dissertation/Thesis / Masters Thesis Psychology 2018