Browsing by Subject "Polymeric composites"
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Item Analysis of factors affecting effective bond length of fiber reinforced polymer composite laminate externally bonded to concrete substrate(2012-05) Athawale, Parth; Bae, Sang-Wook; Morse, Stephen M.; Chen, XinzhongBond length is one of factors which are important with regards to the effective technique of improving the shear capacity of a concrete member by externally bonding fiber reinforcement polymer laminates. A number of models have been proposed by various researchers over the years but there is not a single model that can definitely predict the effective bond length (effective bond length). The models proposed show a disparity between the analytical and experimental values. This study takes a holistic approach to rationalize all the influencing factors. FEA is done of the existing experimental test results by calibrating for measured failure load and effective bond length values. A sensitivity study is undertaken to understand the influence of the affecting parameters on shear stress and effective bond length.Item Development of a CFRP system to provide continuity in existing reinforced concrete buildings vulnerable to progressive collapse(2007) Orton, Sarah Lynn, 1978-; Jirsa, James O.; Bayrak, Oguzhan, 1969-Reinforced concrete buildings may be vulnerable to progressive collapse due to a lack of continuous reinforcement. Progressive collapse is an extreme form of collapse that is disproportionate to the originating cause. Such collapses cause not only significant damage to buildings, but also greater loss of life and injuries. Carbon fiber reinforced polymer (CFRP) may be used to retrofit existing reinforced concrete beams and provide the missing continuity needed to resist progressive collapse. This research focuses on retrofitting the beams in a reinforced concrete building to provide sufficient continuity to reach catenary action. The catenary action may allow the beam to carry vertical loads at large displacements if a supporting column were removed. The CFRP can provide continuity through the negative moment reinforcement or through the positive moment reinforcement. The research was broken into three major components. Anchorage tests form the design basis of the CFRP retrofit and ensure that the capacity of the retrofit can be accurately predicted. Continuity tests determine if the CFRP retrofit is capable of providing continuity and if the retrofit will allow the beam to reach catenary action and sustain a load representing resistance to progressive collapse. The analysis model forms a set of equations for catenary action so the results can be applied to reinforced concrete beams in general. Forty anchorage tests, eight continuity tests, and one analysis model were constructed and evaluated. The anchorage tests found that carbon fiber anchors enabled improved utilization of the tensile capacity of a CFRP sheet and improved the efficiency of material usage in CFRP retrofits. The continuity tests found that beams without continuous reinforcement can reach catenary action (depending on design details) and a CFRP retrofit, if designed correctly (placed in locations that do not cause rebar fracture before catenary), may be able to reduce vulnerability to progressive collapse. The analysis model was able to accurately predict the load-deflection behavior of a reinforced concrete beam in catenary action. The overall conclusion is that a CFRP retrofit can reduce vulnerability to progressive collapse in reinforced concrete buildings.Item Integral-skin formation in hollow fiber membranes for gas separations(2001-12) Carruthers, Seth Blue; Koros, William J., 1947-; Willson, C.G., 1939-The morphologies of polymeric integrally-skinned asymmetric gas separation membranes are typically visualized as a thin selective skin region supported by a low resistance porous structure. Improvements in scanning electron microscopy (SEM) now allow for combinatorial analysis of this visualization with gas permeation measurements for previously reported ultra-thin defect-free hollow fiber membranes. The fibers were formed via a dry-jet, wet quench process with a spinning solution comprised of Matrimid polyimide and components of varying volatility. Depending on the formation conditions, the fibers displayed either defect-free skin layers or lower selectivity nodular skin morphologies. Under ideal conditions, defect-free skin thicknesses of 130 nm were characterized by O2, N2 and He permeation in conjunction with SEM studies. A fiber forming technique has allowed for the quick characterization of the skin layer via SEM analysis. The fiber forming technique, high-resolution SEM analysis and gas permeation measurements have allowed for a more complete understanding of defect-free skin formation. Typical solvent exchange techniques did not have a significant influence on the formation of the defect-free skin layer, although a critical point drying method was able to produce membranes with initial gas permeances twice those of conventionally dehydrated hollow fibers. Skin formation was found to primarily be influenced by the evaporation of volatile components from the nascent skin layer in the air gap. Phase separation of the polymer solution in the nascent skin layer was found to be detrimental to skin formation. The one-phase nascent skin layer is suggested to be kinetically hindered from phase separating due to the relative immobility of the polymer chains before immersion into the quench bath. The polymer chain mobility for different potential membrane forming dopes are compared using polymer physics models. Qualitative evidence suggests that lower molecular weight Matrimid samples may be formed into defect-free membranes if the initial dope is 40% wt. polymer, as suggested by the scaling of the previous defect-free membrane system by the Rouse model.Item Nanocomposites of poly(acrylonitrile-butadiene-styrene) and montmorillonite clay: dispersion and mechanical properties(2005) Stretz, Holly Ann; Paul, Donald R.