The object of this study is to incorporate a nonlinear material law for wood in the finite element program ABAQUS to develop effective finite element models of glulam domes, and to investigate the buckling behavior of glulam domes using this finite element program. The material law is implemented with a FORTRAN subroutine. Results from thorough testing of the subroutine are presented. The dome is then modeled with I-DEAS and, analyzed with ABAQUS. The modeling procedure is briefly discussed, and the results from the stability analysis of the dome are presented. Finally, conclusions and further research scope based on this study are presented. / Master of Science

The influence of crenulated noncircular fibers on the micromechanical stress states due to a transverse strain and to a temperature change in carbon/carbon composites is examined using the finite element method. Stresses at the interface of both fully bonded and fully disbonded fibers having two crenulation amplitudes and with two fiber volume fractions are presented. In each case, these interface stresses are compared to stresses at the interface of circular fibers which have the same degree of disbond and fiber volume fraction and are under the same loading conditions. For the disbonded cases, deformed meshes showing locations of fiber/matrix contact are also included. In addition to the interface stress states, selected composite properties are also computed and compared in each case examined. Interest in studying noncircular fibers stems from a desire to increase the transverse properties of carbon/carbon by introducing a mechanical interlocking between the fiber and the matrix. Results presented here indicate that this interlocking does in fact occur. Evidence from the interface stress data suggests, however, that any possible advantage of this interlocking may be outweighed by the disadvantage of stress concentrations which arise at the interface due to the crenulated geometry of the fibers / Master of Science

Eight identical and independent pilot scale recirculating aquaculture production systems were populated with fingerling hybrid striped bass <i>(Morone chrysops</i> female x <i>Morone saxatilis male</i>). Three population densities were established with two replicates at 132 fishlm3 and three replicates each at 66 and 33 fishlm3. Water chemistry and water quality characteristics were monitored throughout the 228 day growth trial for all eight systems. A system component performance analysis was done for both the multi-tube solids clarifier and rotating biological contactor (RBC). Water chemistry and water quality analysis included dissolved oxygen (DO), alkalinity, ions, carbonaceous biochemical oxygen demand (CBODS), chemical oxygen demand (COD), dissolved organic carbon (DOC), total suspended solids (TSS), volatile suspended solids (VSS), total ammonia nitrogen (TAN) , nitrite and nitrate. The major ions present were chloride, nitrate, sulfate, phosphate, sodium, calcium, magnesium and potassium. Trace levels of TAN, nitrite, iron and copper were also observed. Sodium, calcium and chloride levels were controlled based on a preplaned water exchange and chemical management method. TAN, nitrite and nitrate levels increased over time with increasing feed rates but never reached levels toxic to the fish population. CBODS,COD, DOC, TSS and VSS increased over time increasing as a function of increasing feed rates. No correlation was observed between fish mortality or fish growth rates for the range of organic and solids parameters observed during this study. On average 67% of the TSS present was between 1.5 and 30 microns in size. Diurnal cycles were observed for DO, TAN and alkalinity. The magnitude of these cycles were population dependent. Multi-tube clarifiers removed an average 56% of all suspended solids in a single pass with 81 % removal efficiency for particles above 70 microns in size. Analysis of the system effluent generated by the clarifier indicates a high degree of similarity between the aquaculture effluent and standard municipal waste on a nutrient basis but with much higher levels of nitrogen and phosphate species. RBC nitrification performance was fitted to an empirical equation. A nearly constant TAN removal rate was observed over the range of mass loading experienced in this growth trial. This implies that within a reasonable range higher flow rates resulting in higher mass loading will yield higher TAN removal rates for a given RBC. / Master of Science

Previous research relating to alum sludge land application has primarily been restricted to laboratory studies of short-term environmental effects. In general, most research has concluded that the environmental effects of alum sludge constituents can be easily controlled. This study investigated the fate of land-applied alum sludge constituents nearly three years after incorporation into a Slagle soil. An existing field site was used. The site had been used for a pilot study examining the land application of alum sludge from the Harwood's Mill Water Treatment Plant in Newport News, Virginia. Alum sludge and lime were applied to the site in November, 1989. Soil, soilwater, groundwater and pine needle tissue media were sampled during the summer of 1992. It was determined that the alum sludge posed no observable long-term threat to groundwater quality or vegetative productivity. Migration of alum sludge constituents through the soil profile could not be confirmed in this research. However, acid precipitation may have destroyed the alkalinity added to the soil. Thus, long-term management of alum sludge land application to acid soils may require additional increments of alkalinity. / Master of Science

The Illinois Institute of Technology Research Institute (IITRI) composite compression test method is probably the most widely accepted as producing accurate results. Difficulties associated with the application of this method, however, have fueled continued research into alternate methods. In this study, the Wyoming End-Loaded Side-Supported (ELSS) test scheme was investigated in a combined shear/end loaded mode. This system was examined experimentally and analytically to establish the method as a reasonable alternative to IITRI testing. Combined shear/end loading was accomplished by applying a controlled amount of clamping force to the stabilizing blocks, allowing them to transmit shear force to the coupon faces through friction. The fabrication of test specimens from a BASF graphite IBMI material system is described in detail, including the application of a novel "press-clave" processing system developed at Virginia Tech. This system allows for cost-effective manufacture of flat panels under conditions similar to autoclave processing. For the material system employed in this study, this process proved superior to conventional hot press processing. Experimental results include strengths and failure modes for both tabbed and untabbed coupons tested by the combined loading ELSS method, and these data are compared to the results by the IITRI method. Strength was found to increase with increasing clamping, but reached a maximum with both untabbed and tabbed specimens. The maximum strength achieved with untabbed specimens was still significantly below the IITRI value, but the tabbed specimens reached strengths comparable to the IITRI data. The failure mode also changed with increased clamping, from end crushing to brooming with untabbed specimens, and from end crushing to shear failure with tabbed specimens. As the strength and failure mode achieved with the combined loading ELSS method using tabbed specimens are both similar to those seen in the IITRI tests, this modified technique can be considered equivalent to the IITRI method. Preliminary data from tests using novel nonbonded tabs were also similar to those given by the IITRI method. The finite element method was used to analyze the effect of increasing the clamping force. Competing effects of locally complex and severe stresses at the coupon end and a stress concentration which develops at the end of the gage section were shown to limit the maximum strength. Tabs appear to reduce the stress concentration while further decreasing the stresses at the end, allowing results comparable to those given by the IITRI method to be achieved. / Master of Science

This study was conducted to investigate the factors that affect the duration of breastfeeding in low and middle income women, and to determine if low income women have a greater incidence of decreased duration of breastfeeding. Specifically, the effects of early introduction of formula and solid food and mother’s perceived inadequate milk supply, on the duration of breastfeeding, was researched. A questionnaire was developed and one on one interviews conducted on 147 women who breastfed a baby within the past five years. Data analysis included crosstabulation of selected variables, descriptive analyses, and chi square analyses. Results indicated that the majority of the women surveyed introduced formula early, were long term breastfeeders, between the ages of 30-39, and college graduates. There was no difference in duration of breastfeeding between women of low and middle incomes, however, women of middle income terminated breastfeeding early to return to work or school and tended to introduce formula earlier than low income women. Furthermore, mothers who introduced formula or solid foods early, were generally short term breastfeeders. Mothers who introduced formula and solid foods early cited insufficient milk supply as their main reason for terminating breastfeeding. Therefore, mothers perceived to have an insufficient milk supply, tend to introduce formula and solid foods early, thus, contributing to a possible decrease in duration of breastfeeding. / Master of Science

An elasticity solution is presented for the static equilibrium equations of an axisymmetric composite cylinder under loadings due to embedded piezoelectric laminae. The solution is used to study both uniform and non-uniform distributions of the piezoelectric effect and results are verified using the finite element method. A cylindrical truss element actuator is developed based upon this analysis and shown to be useful in damping vibrations of truss-type structures. It has also been shown that by varying the distribution of the piezoelectric effect. spatially, modal actuators capable of actuating specific modes of axial vibrations in a bar can be developed. Finally, the effects of a piezoelectric patch have been investigated. The axial forces generated at the fixed ends of a cylinder are demonstrated to be proportional to the length of the patch. / Master of Science

The influence of layer waviness in thick cross-ply composite cylinders subjected to hydrostatic pressure is investigated. The cylinders considered are graphite-epoxy with a 2: 1 ratio of circumferential to axial layers. All cylinders considered contain 104 total layers with a layup of [90/(90/0/90h71s, where a '0° 1 layer is taken to be in the axial direction. The influence of a single isolated group of wavy layers in an otherwise perfect cylinder is evaluated. Layer waviness in only the circumferential direction is considered, and the analysis is assumed to be valid only away from the cylinder ends. A parametric investigation is performed to determine the combined influence of wave location, wave amplitude, and cylinder geometry on hydrostatic response of the cylinder, particularly the stresses generated in and around the wave. The wave is assumed to be located either at the inner or the outer radius of the cylinder. Three wave amplitudes, 0, are considered: 1/2, 1, and 2 layer thicknesses. Only waves with a half wave length of 10 layer thicknesses are considered. Three cylinder geometries are considered, specifically ones with radius to thickness ratios of 5, 10, and 20. Finite element analysis is used to determine the stress state within the imperfect, i.e., wave included, cylinders. Based on a maximum stress failure criterion, failure pressures are determined for each of the various wave and cylinder geometries. Failure pressures for the imperfect cylinders are compared with those for a perfect cylinder to determine the failure pressure reduction ratios due to fiber waviness. It is shown that pressure capacity reductions of approximately 50% are possible for the range of parameters studied. Failure is primarily due to fiber compression, though interlaminar shear and interlaminar tension are a factor. Finite element analysis is also used to deter ine the failure pressure of the perfect cylinder due to buckling. This is done to determine whether failure due to buckling may overshadow material failure due to fiber waviness. It is shown that buckling is a factor in only one of the cylinder geometries considered, and only in the cases of mild layer waviness. In addition to results, details about the finite element model are presented. These details include geometry of the wave, changes in material properties due to local fiber rotation and local volume fraction changes, boundary conditions, and justifications for modeling simplifications that were made in an effort to reduce computational costs and analysis times. / Master of Science

There are two basic methods used to analyze and design reinforced concrete members for shear, the American Concrete Institute Code method (used in the United States) and the truss model method (used in different European Codes and in the Canadian Codes). The ACI Code method is a semi-empirical solution since it builds on fitting actual test results to the analytical mechanism method. Although it will lead to safe results, the ACI method lacks a physical model to represent the actual forces in the beam. For this reason, attention is increasingly being given to develop a mechanical-mathematical model to show the actual behavior of the beam failing in shear. The truss model theory provides a more promising way to treat shear since it can model the structural action in the beam. It was first proposed by Ritter and Marsh at the turn of the twentieth century. The concept has been extended by recent work of Lampert and Thürlimann (1971), Collins and Mitchell (1980), MacGregor (1988), and others. The purpose of this study is to compare the ACI method and the truss model method for the design of reinforced concrete slender and deep beams. The results of this study suggest that the truss model is better suited for the design of deep reinforced concrete beams because it models the dominant mechanism that happens in the beam which is the force transfer from load to reaction by the direct compression struts. For slender reinforced concrete beams, either method is suitable for design. / Master of Science

An experimental study was performed to investigate the integrity of gloveboxes when subjected to lathe drip pan fires. These fires are potentially dangerous since glovebox failure may allow hazardous gases to escape containment. A full scale mockup of a glovebox and corresponding air flow system was constructed. Careful consideration was given to the two components expected to cause glovebox failure: the gloves and windows. In addition to normal tests, tests which introduced added ventilation openings (i.e. missing gloves, missing window) were also performed. The glovebox ventilation system places these fires in the category of overhead forced ventilation compartment fires. Since little data has been obtained previously for this type of fire, further experiments were conducted to determine the effect of fuel surface area on fire behavior. In the past, these fires have been successfully modelled as well-stirred reactors. Results showed that overall containment was achieved under normal glovebox conditions. Added ventilation opening tests, however, showed that these scenarios would lead to a loss of containment. Nevertheless, under no conditions did a catastrophic glovebox failure occur. Furthermore, experiments with reduced fuel surface areas showed that the fires became less hazardous as the pan diameter decreased. Exhaust gas concentrations, temperature data, burn rates, smoke generation, and heat releases were the criteria used to form this conclusion. Neither a well-stirred or two-layer environment was observed. / Master of Science