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This thesis presents elastic-plastic finite element analyses of seven long span composite open-web steel joists. These analyses account for the incomplete interaction between the concrete slab and the steel joist by modeling the nonlinear behavior of the steel shear connectors. Experimental tests on long span composite open-web steel joists were performed at Virginia Polytechnic Institute and State University. Measurements of joist deflections, member strains, and slip between the concrete slab and steel joist were recorded. The response of the finite element models agree reasonably well with the response of the test prototypes where the shear connector position was known. The finite element model can be generated on any general purpose finite element program that includes beam elements and nonlinear spring elements. The finite element model can give reasonable predictions of deflections and ultimate load capacity of a composite open-web steel joist. / Master of Science

In this study two one-dimensional finite element formulations based on higher-order displacement models have been developed. Both theories account for geometric nonlinearities, a parabolic shear strain distribution through the thickness, and satisfy the shear stress free boundary conditions at the upper and lower surfaces of the beam. The theories also account for the bend-stretch, shear-stretch, and bend-twist couplings inherent to generally laminated composite beams. Further, a coupling between the shear deformation and the twisting is introduced. The lateral strains are assumed nonzero and retained in the formulation. The first model termed SVHSDT also accounts for the continuity of the interlaminar shear stresses at the layer interfaces, while keeping the number of degrees of freedom independent of the number of layers. This theory though is restricted to the analysis of symmetrically laminated cross-ply beams. The formulation has been applied to the linear static and free vibration analysis. The second model termed RHSDT is valid for generally laminated beams. This model has been applied to the nonlinear static and transient analysis of generally laminated beams, free vibration analysis, and impact analysis. The effect of axial stresses on the nonlinear transient response has also been investigated using this theory. For generally laminated beams the lateral strains and the shear-twist coupling were found to have a significant effect on the vibrations frequencies. Also, as expected, initial stresses, boundary conditions and the lamination scheme were found to have a significant effect on the nonlinear responses. / Master of Science

To better understand the behavior of composite beams in buildings, push-out tests were conducted to study the behavior of welded shear studs. Forty-eight solid slab push-out tests were conducted to study how stud tensile strength and concrete properties affect the strength of shear connections. It is shown that raising the tensile strength of a shear connector actually has an adverse effect on the connector's performance and strength. It is also shown that the upper limit for shear strength used in the current AISC specification (Load 1993) is unconservative and a lower upper limit is proposed. Eighty-seven pushout tests utilizing steel deck were also conducted. It is shown how the placement, height, and arrangement of shear studs, as well as the height and gage of steel deck affects the strength of shear connections when stiffened steel deck is used. It is shown that the current AISC specification is unconservative and does not account for the many failure mechanisms associated with connections using steel deck. It is shown how tension within the stud shank, friction at the slab/beam interface, and steel deck strength affect the strength of shear connections. / Master of Science

Composite materials are increasingly finding use in structures, such as aircraft components, and thus, an accurate method of predicting response is required. Even laminated structures that are considered thin can be significantly affected by transverse shear effects, and as a result, transverse shear should not be neglected. The free vibration response of generally-laminated, thick, skew, trapezoidal plates is investigated as there appears to be a lack of information in this area. In the method developed, Chebychev polynomials are used as displacement functions in the Rayleigh-Ritz method. Various edge supports are considered, and appropriate linear and rotational springs are introduced to approximately satisfy the essential boundary conditions associated with simply-supported and clamped edges. First-order shear theory is used to account for transverse shear effects, and rotary inertia is also included.in the model. Convergence of the solution resulting from changes in spring values and number of terms in the series is investigated. The accuracy of the method is demonstrated by comparing the present method to available results for plates of various quadrilateral shape, material systems, and boundary conditions. Thick laminated plates of both symmetric and unsymmetric construction and of various planforms and boundary conditions are then presented. Cantilever, thick, skew, and trapezoidal plates are then extensively studied, and variations in natural frequencies due to geometric parameter changes, such as taper ratio, sweep angle, and value of the parameter q, are discussed. The parameter, q, is a root length multiplier which determines the length of the quarter-chord line, thus representing a measure of the span. Mode shapes for a number of plates of various planform and support conditions are included. / Master of Science

The purpose of this study was to determine how chemical conditioning agents and mechanical dewatering devices affect sludge dewatering with respect to shear. Bench scale experiments were performed to determine the effect of shear and mole charge on polymer dose requirements using anaerobically digested sludge. Lime, ferric chloride, and polymer were used to condition anaerobically digested sludge to evaluate the influence of these conditioning agents, separately and in combination, on shear resistance. Dewatering studies were performed using a plate and frame press, a centrifuge, and a screw press to determine the amount of shear within each device and to develop a means of estimating polymer dose for each device. It was determined that increased molecular charge of polymer decreased chemical dose requirements and improved shear resistance. Both lime and ferric chloride improved sludge dewatering rates but only ferric chloride conditioned against shear. Ferric chloride addition prior to polymer conditioning improved sludge shear resistance, improved the dewatering rate (CST), and decreased the required polymer dose. The dewatering study using the plate and frame press verified that polymer dose could be estimated using CST values and a Gt value of approximately 30,000. Also, ferric chloride in combination with polymer improved filtrate quality, increased the cake solids concentration, and increased the filtrate volume throughput of sludge conditioned with lower polymer doses than if polymer alone was used. The dewatering study using a high speed centrifuge found that polymer dose could be estimated using CST values at a Gt between 10,000 and 20,000 or by use of the wedge zone simulator. The dewatering study of the screw press found that CST values and the wedge zone simulator under predicted polymer dose. This was thought to be the result of shear in the feed system prior to dewatering. / Master of Science

Abstract not available

The genetic disorder sickle cell anemia causes hemolytic anemia and sickle pain crisis, episodes of microvascular occlusion resulting in painful ischemic tissue damage. Pain crisis is thought to occur when sickle erythrocytes adhere in the post-capillary venule, partially occluding the vessel. The resulting slowed blood flow causes more extensive cell adherence and entrapment of rigid, deoxygenated erythrocytes until the vessel is entirely occluded. It was hypothesized that the inflammatory mediators histamine and tumor necrosis factor-, factors known to cause endothelial expression of adhesive ligands, might significantly increase sickle erythrocyte adhesion, and thus be capable of initiating sickle pain crisis. It was also hypothesized that the perfusion shear stress environment of the endothelium, known to be oscillatory and reduced in sickle cell patients, was a significant mediating factor of sickle cell adhesion. An in-vitro flow chamber using cultured endothelial cells and erythrocytes from blood samples of sickle cell anemic patients was used to quantify sickle erythrocyte adherence to stimulated and unstimulated endothelial cells under shear stresses from 1.0 to 0.1 dyne/cm2. Results showed that both endothelial stimulation and reduction of the perfusion shear stress increased sickle erythrocyte adherence. In combination, the use of inflammatory stimulation with reduced shear stress resulted in further increased adhesion, but only when above the range of 0.1 V 0.2 or 0.4 dyne/cm2, depending on the inflammatory mediator. Adhesion below this level of shear is not significantly increased by endothelial stimulation. The mechanism by which histamine mediates adhesion was investigated, and found to involve the endothelial H2 and H4 receptors and expression of the P-selectin ligand. These data suggest that irregular flow, typical of sickle microvasculature, may act in conjunction with the pro-inflammatory state of sickle vasculature and the histaminergic nature of some pain treatments to initiate or propagate sickle vaso-occlusion. Findings concerning histamine, tumor necrosis factor-alpha, and shear stress effects on adherence are discussed in relation to their possible applicability to patient health, future studies are outlined to confirm the relation of in vitro data to in vivo patient condition, and proposals are made for applying these methodologies to other potential mediators of sickle erythrocyte adhesion.

Bileaflet mechanical heart valves (BMHVs), though a life-saving tool in treating heart valve disease, are often associated with serious complications, including a high risk of hemolysis, platelet activation, and thromboembolism. One likely cause of this hyper-coagulative state is the nonphysiologic levels of stress experienced by the erythrocytes and platelets flowing through the BMHVs. Research has shown that the combination of shear stress magnitude and exposure time found in the highly transient leakage jet emanating from the b-datum gap during valve closure is sufficient to cause hemolysis and platelet activation. Regions of flow stasis in the valve vicinity may also allow activated platelets to aggregate and form thrombus. This thesis addresses the hypothesis that passive flow control may have the potential to reduce flow-induced thrombogenicity by altering the fluid mechanics of bileaflet mechanical heart valves. To test this hypothesis, a steady model of the regurgitant b-datum line jet was developed and studied. This model served as a test bed for various vortex generator array designs. The fluid mechanics of the b-datum line jet model was investigated with flow visualization and particle image velocimetry. In vitro tests with whole human blood were performed with and without the vortex generators in order to determine how the presence of the passive flow control affected the propensity of the blood to form thrombus. An effort was then made to correlate the fluid mechanics of the jet model with the procoagulant potential results from the blood experiments. The effect of the vortex generators on the fluid mechanics of the valve under physiologic pulsatile conditions was also investigated via flow visualization in the Georgia Tech Left Heart Simulator. By studying a steady model of the regurgitant b-datum line jet, it was found, using an in vitro system with whole human blood, that the presence of vortex generators significantly decreased the blood's propensity for thrombus formation. The potential of applying passive flow control to cardiovascular hardware in order to mitigate the injurious effects of shear-induced platelet activation is thus demonstrated. The investigation into the effect of vortex generators on the fluid mechanics of the b-datum line jet showed that the jet oscillated aperiodically and that the effect of the applied flow control was played out at both the scale of the chamber (large-scale) and on the scale of the vortex generator fins (small-scale). On the large scale, the presence of vortex generators appeared to decrease the magnitude or frequency of jet oscillation, thereby stabilizing the jet. After removing the effect of the large-scale oscillations via phase averaging, the effect of the vortex generators on the small scale was examined. On the small scale, the jet without flow control was found to have higher levels of velocity RMS, particularly on the jet periphery, and higher levels of Reynolds shear stress. It is proposed that the vortex generators effect this change by generating vorticity in the plane of the jet. This vorticity is theorized to stabilize the jet, delaying roll-up of the jet shear layer which occurs via the Kelvin-Helmholtz instability. The method by which the vortex generators acted on the fluid mechanics of the steady jet system to decrease the blood's procoagulant potential was investigated via flow visualization and DPIV. The results from these studies implicate two possible mechanisms by which the vortex generators may act. First, the peak turbulent shear stresses in the jet were reduced by 10-20% with the application of vortex generators. Even if only a few platelets were activated in each passage through the valve, the cumulative effect of this difference in peak stresses after many passes would be greatly magnified. Thus, this reduction in turbulent shear stresses may be sufficient to explain the change seen in the blood's procoagulant potential with the application of passive flow control. It is suspected, though, that the second mechanism is dominant. The flow fields revealed that the presence of the vortex generators delayed or prevented the roll-up of the Kelvin-Helmholtz instability in the b-datum jet's shear layers into discrete vortices. By doing so, it is thought that opportunities for the interaction of activated and unactivated platelets entrained in these vortices were prevented, thereby inhibiting further propagation of the coagulation cascade. Even if the rate at which platelets were activated was similar for cases with and without flow control, it seems that the flow fields experienced by the platelets subsequent to activation can determine the level of procoagulant potential. Under the steady conditions observed in this experiment, the jet influenced by vortex generators was thus shown to induce significantly lower levels of procoagulant potential.

In this research, monotonic and cyclic tests on cold-formed steel shear walls sheathed with steel sheets on one side were conducted to (1) verify the published nominal shear strength for 18-mil and 27-mil steel sheets; and (2) investigate the behavior of 6-ft. wide shear walls with multiple steel sheets. In objective 1: this research confirms the discrepancy existed in the published nominal strength of 27-mil sheets discovered by the previous project and verified the published nominal strength of 18 mil sheet for the wind design in AISI S213. The project also finds disagreement on the nominal strength of 18-mil sheets for seismic design, which is 29.0% higher than the published values. The research investigated 6-ft. wide shear wall with four framing and sheathing configurations. Configuration C, which used detailing, could provide the highest shear strength, compared to Configurations A and B. Meanwhile, the shear strength and stiffness of 2-ft. wide and 4-ft. wide wall can be improved by using the seismic detailing.