The present study aims to explore dynamical behavior of the fluid-elastic instability of a circular cylinder in shear flow by numerical simulations. The theoretical model comprises two groups of transient conservation equations of mass and momentum and the governing equations are solved numerically with an iterative SIMPLEC(Semi-Implicit Method for Pressure-Linked Equations Consistent) algorithm to determine the flow property and to analysis structure stress simultaneously. Additionally, the TFI (Transfinite interpolation) computation procedure is applied to characterize the behavior of fluid-structure interaction. The predictions are in reasonable agreement with literature showing the validity of the present theoretical model. The numerical results indicate that there is a transverse force acting from high velocity side toward the low velocity side in shear flow. The magnitude of this transverse force increases with the shear parameter. The Strouhal number slightly increases as the shear parameter increases for all Reynolds number. As the pattern of the approach flow changes from the uniform to shear flow, the front stagnation point shifts to high velocity side, and the base pressure increase. The magnitude of the shift of front stagnation point is linear with the shear parameter. Furthermore, this study appraises the amplitude and orbit of fluid elastic vibration of a circular cylinder in shear flow, and shows the effects of the spring constant and damping factor on fluid elastic vibration of the cylinder. In addition, various effects including shear parameter and mass ratio on the critical velocity of the fluid elastic vibration also has been examined detail.

The effects of microbubbles injection in the boundary layer of a turbulent channel flow are investigated. Electrolysis demonstrated to be an effective method to produce microbubbles with an average diameter of 30 ??m and allowed the placement of microbubbles at desired locations within the boundary layer. Measurement of velocity fluctuations and the instantaneous wall shear stress were carried out in a channel flow facility. The wall shear stress is an important parameter that can help with the characterization of the boundary layer. This parameter can be obtained indirectly by the measurement of the flow pressure at the wall. The wall shear stress in the channel was measured by means of three different independent methods: measurement of the pressure gradient by a differential pressure transducer, Particle Image Velocimetry (PIV), and an optical wall shear stress sensor. The three methods showed reasonable agreement of the wall shear stress values for single-phase flow. However, differences as skin friction reductions were observed when the microbubbles were injected. Several measurements of wall-pressure were taken at various Reynolds numbers that ranged from 300 up to 6154. No significant drag reduction was observed for flows in the laminar range; however, a drag reduction of about 16% was detected for turbulent Reynolds numbers. The wall-pressure measurements were shown to be a powerful tool for the measurement of drag reduction, which could help with the design of systems capable of controlling the skin friction based on feedback given by the wall-pressure signal. The proposed measurement system designed in this work has capabilities for application in such diverse fields as multiphase flows, drag reduction, stratified flows, heat transfer among others. The synchronization between independent systems and apparatus has the potential to bring insight about the complicated phenomena involved in the nature of fluid flows.

The aerodynamic steering forces and moments on a wind tunnel model of an axisymmetric bluff body are altered by induced segmented attachment of the separated flow over an azimuthal Coanda surface. The model is suspended in the wind tunnel by eight thin wires for minimal support interference within the wake. Each wire is instrumented with a miniature strain gage sensor for direct dynamic force measurements. Control is effected by an array of synthetic jet actuators that emanate from narrow, azimuthally-segmented slots, within a backward facing step. The aerodynamic effects are characterized using hot-wire anemometry and PIV measurements. In the first set of experiments, the array of synthetic jets is distributed around the perimeter of the circular tail end which is extended into a Coanda surface. The fluidic actuation results in segmented vectoring of the separated base flow along the rear Coanda surface and induces asymmetric aerodynamic forces and moments that can effect steering during flight. Transitory modulation of the actuation waveform of multiple actuators around the tail leads to the generation of significant dynamic side forces of controlled magnitude and direction with the potential utility for flight stabilization and fast maneuvering. In a second set of experiments the array of the synthetic jets is placed upstream of a mid-body axisymmetric cavity. A single jet induces a quasi-steady, nearly-matched force couple at the upstream and downstream ends of the cavity. Furthermore, transitory activation of multiple jets can be used to control the onset and sequencing of the couple forces and therefore the resultant force and moment.

Strain localization, the phenomenon of large shear deformation within thin zones of intensive shearing, commonly occurs both in-situ and in the laboratory tests on soils specimens. The intriguing mechanism of strain localization and how it will affect the general behavior of soil specimens have been investigated by many researchers. Some of the efforts have focused on finding the links between material properties (void space, fabric tensor) and mechanical behavior (stress, strain, volumetric strain). In the last ten years, several extensive studies have been conducted at Georgia Tech to investigate the mechanism of strain localization and link the microstructural properties with the engineering behavior of Ottawa sands. These studies have included 2-D and 3-D characterization of soil microstructures under either triaxial or biaxial shearing conditions. To extend and complement these previous studies, the current study focuses particularly on 3-D reconstruction, analysis and modeling of specimens of Ottawa sand subject to triaxial or biaxial loading. The 3-D microstructure of biaxial specimens was reconstructed using an optical microscopy based montage and serial sectioning technique. Based on the reconstructed 3-D digital volumes, a series of 2-D and 3-D characterizations and analyses, including local void ratio distributions, extent of shear bands, influence of soil fabrics and packing signature effects, were conducted. In addition to the image analysis based reconstruction and characterization, the 3-D discrete element method (DEM) code, PFC3D, was used to explore both biaxial and triaxial shear related soil behaviors at the global and particulate scale. Void ratio distributions, coordination numbers, particle rotations and displacements, contact normal distributions and normal contact forces as well as global stress and strain responses were investigated and analyzed to help understand the mechanism of strain localization. The microstructures of the numerical specimens were also characterized in the same way as the physical specimens and similar strain localization patterns were identified. Combined with the previous related studies, the current study provides new insights into the strain localization phenomenon of Ottawa sands subject to triaxial and biaxial loading. In addition, the reconstructed digital specimens were subject to a series of dissection studies which revealed exciting new insights into "microstructure signatures" which exist at both meso and micro scales within the real and simulated specimens.

This thesis describes part of the work associated with Project 0-6719 sponsored by the Texas Department of Transportation (TxDOT). The primary objective of the project is to examine the feasibility of strengthening older continuous multi-span steel girder bridges through the use of post-installed shear connectors. Bridges potentially eligible for retrofit have noncomposite floor systems, where the concrete slab is not attached to the steel girders with shear connectors. Many of these bridges were designed in the 1950's and 1960's for loads smaller than the standard design loads used today. A secondary objective of the project, and the main focus of this thesis, is to examine the design of post-installed shear connectors for fatigue. Of particular interest in this study is the adhesive anchor, given its convenient installation procedure but relatively poor fatigue performance in previous tests. The objectives of this thesis were to quantify the fatigue strength of the adhesive anchor, as well as quantify the shear force and slip demands on adhesive anchors in realistic bridge conditions. In regards to the first objective, twenty-six direct shear fatigue tests were performed on adhesive anchors. Each test was conducted on a single adhesive anchor in order to capture its individual cyclic load-slip behavior. Results indicate that adhesive anchors have considerably higher fatigue strength than conventional welded shear studs, making partial composite design feasible in the strengthening of older steel bridges. In regards to the second objective, analytical and computational studies were conducted on composite beams with adhesive anchors. Results show that the shear force and slip demands are typically smaller than the endurance limits determined from direct-shear testing. This suggests that fatigue failure of adhesive anchors under service loads may not be a primary concern. Based on the results, preliminary recommendations for the design of adhesive anchors for fatigue are provided. / text

Flat slab-column connections are common elements in reinforced concrete (RC) structures such as parking garages. In cold weather regions, these structures are exposed to de-icing salts and aggressive environments. Using fiber reinforced polymer (FRP) bars instead of steel in such structures will overcome the corrosion problems associated with steel reinforcement. However, the available literature shows few studies to evaluate the behaviour of FRP-RC interior slab-column connections tested mainly under concentric loads, which seldom occurs in a real building. The main objectives of this research are to deal with this gap by investigating the behaviour of full-scale glass (G) FRP-RC interior slab-column connections subjected to eccentric load and to provide design recommendations for such type of connections. This study consisted of two phases, experimental and analytical. The experimental phase included the construction and testing of ten full-scale interior slab-column connections. The parameters investigated in the experimental phase were flexural reinforcement ratio, concrete compressive strength, type of the reinforcement, moment-to-shear ratio and the spacing between the shear stud reinforcement. Test results revealed that increasing the GFRP reinforcement ratio or the concrete strength increased the connection capacity. Moreover, compared to the control steel-RC specimen, the GFRP-RC connection with similar reinforcement rigidity showed comparable capacity and deflection at failure. Also, increasing the moment-to-shear ratio resulted in a reduction in the vertical load capacity, while using the shear stud reinforcement enhanced the strength up to 23%. In the analytical phase, a 3-D finite element model (FEM) was constructed using specialized software. The constructed FEM was able to predict the experimental results within a reasonable accuracy. The verified FEM was then used to conduct a parametric study to evaluate the effects of perimeter-to-depth ratio, column aspect ratio, slab thickness and a wide range of flexural reinforcement ratio. The numerical results showed that increasing the reinforcement ratio increased the connection capacity. In addition, increasing the perimeter-to-depth ratio and slab thickness reduced the punching shear stresses at failure, while, the effect of the column rectangularity diminished for a ratio greater than three. Moreover, the results showed prominent agreement with the experimental results from literature. / October 2015

An experimental study was conducted at the Ferguson Structural Engineering Laboratory in order to investigate the shear behavior of 54-inch deep prestressed concrete U-beams. The primary goal of this research was to improve the design and detailing of the skewed end-blocks commonly used in these beams. As U-beams had been in service for several decades without incident, it was anticipated that there would be little need for change in the design, and the findings of the research would involve a slight tweaking to improve the overall performance. Unfortunately, during the first phase of shear testing (testing of the current design standard) it was found that the U-beam was not reaching the code calculated shear capacity. During this phase of testing the premature failure mechanism was isolated as the breakdown of the web-to-flange interface in the end region of the girder. Therefore, the second phase of testing sought to prevent the breakdown of this boundary by three options: (1) increasing the web width while maintaining current levels of mild reinforcement, (2) increasing the web width while also increasing the amount of reinforcement crossing the web-to-flange boundary, or (3) by increasing the amount of reinforcement at the boundary while maintaining the current web width. Two acceptable solutions to the premature failure method were developed and tested during this phase both of which included an increase in the amount of mild reinforcement crossing the web-to-flange interface (with and without an increase in web width). The research into refining of these new details is ongoing as part of the Texas Department of Transportation’s Research Project number 0-5831. / text

The Best Master's Thesis Award of the Hong Kong Section, American Society of Civil Engineers (2005-06) / published_or_final_version / abstract / Civil Engineering / Master / Master of Philosophy

Split Concrete Model (SCM) is a unified approach towards modeling shear behavior in concrete. SCM is essentially a rational model which is evaluated and modified using a large experimental database.The shear strength of the concrete beam is modeled as the sum of the contribution of concrete, transverse reinforcement, longitudinal reinforcement and bond between concrete and longitudinal reinforcement. Concrete does not contribute to the shear strength after the formation of the crack. In SCM, this is shown to be accurately modeled by only considering the second branch of the critical crack while computing the contribution of concrete towards shear strength of the beam. Formation of the second branch of the critical crack and immediate subsequent failure of the beam has been compared to the split-cylinder test, which forms the conceptual basis of SCM.SCM computes the concrete contribution using the split tensile strength and the area under compression of the concrete beam. For cases where a split-cylinder test is not performed, a mathematical model is proposed to compute the split tensile strength using the compressive strength of concrete available from experimental results. This model is proposed using advanced statistical methods, including weighted residuals and Box-Cox transformation and is validated using various statistical procedures. The transverse reinforcement contributes to the shear strength of the concrete beam only after the formation of the crack. In SCM, this is shown to be accurately modeled by only considering the first branch of the critical crack while computing the contribution of the transverse reinforcement towards shear strength of the beam, instead of the conventional approach of considering the entire length of the crack. The contribution of the longitudinal steel and bond between concrete and longitudinal steel and concrete is accurately modeled unlike the conventional approaches which do not consider this contribution.Evaluation using the database shows that SCM can predict accurate results for all ranges of strength, depth, reinforcement ratio, and shear span to depth ratio of the beam. This shows that all the influencing parameters for concrete shear strength have been correctly modeled in SCM. SCM gives more accurate results as compared to current codified approaches as verified with design examples. Finally, specific recommendations have been made indicating how the shear design requirements in the current ACI code can be modified.

The dissertation are analyzing the main characteristics of asphalt concrete influencing shear deformation, appearance and increase of rutting connected with them, analyze the influence of geosynthetic material characteristics onto asphalt concrete functioning.