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In recent earthquakes, structures have not performed as well as expected resulting in a need for better means of retrofitting and improvements in seismic design. Fiber Reinforced Polymers (FRP), as a material with potential to increase strength and ductility of columns in conjunction with capacity design methodology, has promise for seismic design. By investigating the displacement, ductility, and flexural strength properties of FRP confined reinforced concrete circular cross sections, this study analyzes the seismic applications of FRP confinement. The study is performed by incorporating an FRP confined concrete stress-strain model into a developed Moment-Curvature and PM Interaction software. This software conducts a comparison between traditional steel and FRP confined sections while performing parameter studies on the 28-day unconfined concrete compressive strength, longitudinal reinforcing ratio, cross section diameter, FRP confinement jacket thickness-cross section diameter ratio, and FRP confinement system design variables. These studies validate FRP’s performance for seismic applications resulting in several design recommendations to increase displacement capacity, ductility, and flexural strength and, thus, seismic performance.

An accurate and efficient numerical method for Compressible Vorticity Confinement (CVC) was developed. The methodology follows from Steinhoff's vorticity confinement approach that was developed for incompressible flows. In this research, the extension of this approach to compressible flows has been developed by adding a vorticity confinement term as a "body force" into the governing compressible flow equations. This vorticity confinement term tends to cancel the numerical dissipative errors inherently related to the numerical discretization in regions of strong vorticity gradients. The accuracy, reliability, efficiency and robustness of this method were investigated using two methods. One approach is directly applying the CVC method to several real engineering problems involving complex vortex structures and assessing the accuracy by comparison with existing experimental data and with other computational techniques. Examples considered include supersonic conical flows over delta wings, shock-bubble and shock-vortex interactions, the turbulent flow around a square cylinder and the turbulent flow past a surface-mounted 3D cube in a channel floor. A second approach for evaluating the effectiveness of the CVC method is by solving simplified "model problems" and comparing with exact solutions. Problems that we have considered are a two-dimensional supersonic shear layer, flow over a flat plate and a two-dimensional vortex moving in a uniform stream. The effectiveness of the compressible confinement method for flows with shock waves and vortices was evaluated on several complex flow applications. The supersonic flow over a delta wing at high angle of attack produces a leeward vortex separated from the wing and cross flow, as well as bow shock waves. The vorticity confinement solutions compare very favorably with experimental data and with other calculations performed on dense, locally refined grids. Other cases evaluated include isolated shock-bubble and shock-vortex interactions. The resulting complex, unsteady flow structures compare very favorably with experimental data and computations using higher-order methods and highly adaptive meshes. Two cases involving massive flow separation were considered. First the two-dimensional flow over a square cylinder was considered. The CVC method was applied to this problem using the confinement term added to the inviscid formulation, but with the no-slip condition enforced. This produced an unsteady separated flow that agreed well with experimental data and existing LES and RANS calculations. The next case described is the flow over a cubic protuberance on the floor of a channel. This flow field has a very complex flow structure involving a horseshoe vortex, a primary separation vortex and secondary corner vortices. The computational flow structures and velocity profiles were in good agreement with time-averaged values of the experimental data and with LES simulations, even though the confinement approach utilized more than a factor of 50 fewer cells (about 20,000 compared to over 1 million). In order to better understand the applicability and limitations of the vorticity confinement, particularly the compressible formulation, we have considered several simple model problems. Classical accuracy has been evaluated using a supersonic shear layer problem computed on several grids and over a range of values of confinement parameter. The flow over a flat plate was utilized to study how vorticity confinement can serve as a crude turbulent boundary layer model. Then we utilized numerical experiments with a single vortex in order to evaluate a number of consistency issues related to the numerical implementation of compressible confinement. / Ph. D.

A series of tests was performed to consider the behaviour of short composite columns under axial compressive loading, covering a range of S275 and S355 grade steel square hollow section filled with normal and high strength concrete. The interaction between the steel and the concrete component is considered and the results show that concrete shrinkage has an effect on the axial strength of the column. Comparisons between Eurocode 4, ACI-318 and the Australian Standards with the findings of this research were made. Result showed the equation used by the ACI-318 and the proposed Australian Standards gave better predication for the axial capacity of concrete filled SHS columns than the Eurocode 4.

Free-standing ultra-thin films and micro to nanoscale fibers offer a unique geometry in which to study the dynamics of thin film stability and polymer chain dynamics. By melting these films and investigating the subsequent processes of hole formation and growth, and fiber thinning and breakup, many interesting phenomena can be explored, including the nucleation of holes, shear-thinning during hole formation, finite-extensibility of capillary thinning viscoelastic fibers, and confinement effects on entanglement of polymer chains. Free-standing films in the melt are unstable and rupture due to instabilities. The mechanism of membrane failure and hole nucleation is modeled using an energy barrier approach which is shown to capture the dependence of hole nucleation on thickness. The formed holes grow exponentially and are found to grow under a shear thinning, nonlinear viscoelastic, high shear strain regime. These holes impinge upon each other to form suspended fibers. The fibers thin according to a model for the elasto-capillary thinning of the suspended viscoelastic fluid filaments. Monitoring fiber thinning allows for the acquisition of rheological properties as well as the transient, apparent extensional viscosity giving insight into strain hardening and eventual steady-state extensional viscosity. The decay and breakup of these fibers and their interconnected branched structure indicates the effects of confinement on chain entanglement in ultra-thin films. A transition below a critical film thickness, comparable to the dimensions of a polymer chain, shows drastically reduced interchain entanglements and a remarkably faster breakup of suspended fibers. The processes of fiber formation from the melting of ultra-thin films are explored in high detail and produce a new technique for the investigation of rheological and material properties, confinement effects, and the dynamics of thin films and polymer chains.

Single polymer passage through geometrically confined regions is ubiquitous in biology. Recent technological advances have made the direct study of its dynamics possible. We studied the capture of DNA molecules by the electroosmotic flow of a nanopore induced by its surface charge under an applied electric field. We showed theoretically that the DNA molecules underwent coil-stretch transitions at a critical radius around the nanopore and the transition assisted the polymer passage through the pore. To understand how a polymer worms through a narrow channel, we investigated the translocation dynamics of a Gaussian chain between two compartments connected with a cylindrical channel. The number of segments inside the channel changed throughout the translocation process according to the overall free energy of the chain. We found a change in the entropic driving force near the end of the process due to the partitioning of the chain end into the channel rather than the initial compartment. We also developed a theory to account for the electrophoretic mobility of DNA molecules passing through periodic confined regions. We showed that the decrease in the translocation time with the molecular weight was due to the propensity of hairpin entries into the confined regions. To further explore the dynamics of polymer translocation through nanopores, we performed experimental studies of sodium polystyrene sulfonate translocation through α-hemolysin protein nanopores. By changing the polymer-pore interaction using different pH conditions, we identified the physical origins of the three most common event types. We showed that increasing the polymer-pore attraction increased the probability of successful translocation. Motivated by understanding the dynamics of a polymer in a crowded environment, we investigated the dynamics of a chain inside a one dimensional array of periodic cavities. In our theory, the chain occupied different number of cavities according to its confinement free energy which consisted of entropic and excluded volume parts. By assuming that the chain moved cooperatively, the diffusion constant exhibited Rouse dynamics. Finally, we performed computer simulations of a chain inside a spherical cavity. We found that the confinement effect was best described by the hard sphere chain model. We further studied the escape dynamics of the chain out of the cavity through a small hole. The equilibrium condition of the chain during the escape was discussed.

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