Engineering Commons^™

A Comprehensive Protocol For Inspection And Assessment Of Aging Steel Bridges: Experiments, Computations And 3d Laser Scanning Of Field Corroded Girders, Georgios Tzortzinis

Doctoral Dissertations

According to a recent evaluation, our nation's infrastructure has increasingly presenting signs of deterioration with some elements exhibiting significant deficiencies in conditions and functionality. Regarding the transportation network condition, from the over than 600,000 bridges which are included in the National Bridge Inventory, 46,154 of them are characterized as structurally deficient with the backlog of bridge rehabilitation needs estimated at US$125 billion. Among the many aspects of structural deficiency, corrosion is considered a common cause, both for reinforced concrete and steel bridge deterioration. For steel bridges, corrosion has historically triggered bridge failures resulting to fatalities and injuries. To prevent similar …

Critical Buckling And Post-Buckling Behavior Of Thin-Walled Liners Encased By Underground Pipelines In Saturated Soils, Zhaochao Li

Doctoral Dissertations

"This study aims to investigate the structural stability of thin-walled liners encased in functionally-obsolete underground pipelines in saturated soil under external hydrostatic pressure, a concentrated load, temperature change or their combination, and develop a simplified circular arch model of thin-walled liners when not constrained by the pipelines. The friction and adhesion on the interface between a liner and its constraining surface (pipeline or grouting), and the pressure gradient on deeply-buried pipelines are neglected. The critical buckling load of elastic liners is analytically derived under a plane strain condition using the principle of minimum potential energy. The analytical solution is either …

Nanocomposite Polymer Networks For Reconfigurable Materials, Adam W. Hauser

Doctoral Dissertations

This thesis broadly aims to design reconfigurable materials through complementary combinations of nanoparticles and polymers. Understanding nanoparticle dispersion pathways and mechanisms is a critical first step in any polymer nanocomposite work as it continues to be a non-trivial subject. To this end, Chapter 2 describes a simple method to control nanoparticle dispersion within polymer melts by photografting random copolymers to selectively reactive nanoparticle ligands. The chapters following focus on harnessing the functionality of well dispersed nanocomposite networks to elicit macro-scale responses. Chapter 3 exploits the unique optical properties of gold nanoparticles in combination with thermally responsive hydrogels and liquid crystalline …

Post-Wrinkling Behaviors In Layered Elastic Polymers, Anesia D. Auguste

Doctoral Dissertations

Surface instabilities include a variety of different modes such as wrinkles, folds, and creases. Such surface instabilities have been used in numerous contexts including changing the wetting, optical, and mechanical properties of different material surfaces for applications in flexible electronics, tissue engineering and biosensors. Interesting surface morphologies can arise due to differences in pre-strain, stiffness, and thickness between the film and substrate; however, the effects of these differences are not well understood. We have developed an experimental system, complemented by finite element simulations, to systematically vary the pre-stretch of the substrate, modulus contrast and thickness contrast to study the transitions …

Effect Of Processing History And Material Properties On The Growth Of Wrinkle Amplitude, Yu-Cheng Chen

Doctoral Dissertations

Wrinkling has been employed by many organisms to form unique topography, such as fingerprints, gut villi, and surface of flower petal cells. The wavy wrinkle structure provides friction enhancement, surface area increase, optical, and wetting properties improvement. Inspired by Nature, scientists have created wrinkles synthetically and proposed numerous uses for them. However, wrinkling surfaces encounters limitations on achieving massive area and high amplitude-to-wavelength ratio (aspect ratio). The three phase contact line wrinkling technique creates well-defined wrinkles in a continuous fashion, and has great potential to scale-up for massive production. In addition to the velocity dependent adhesion force, we find the …

Studies On The Wrinkling Of Thin Polymer Films Floating On Liquid, Kamil B. Toga

Doctoral Dissertations

This dissertation aims to broaden our understanding on wrinkling instabilities occurring on floating polymeric sheets, and tries to establish innovative methods that exploit these patterns in studies on material behavior and interfacial phenomena. We will address three major topics in this thesis including, i) characterization of the conditions required to buckle an annular disc, ii) characterization of wrinkles occurring around a droplet/bubble placed on a membrane that is kept taut at the liquid-air interface, and iii) using wrinkling patterns as a probe to understand the interfacial behavior and dynamics of ultrathin films. The first project in this thesis is about …

Computational Investigation Of Stress, Contact Conditions, And Buckling Of Thin-Walled Pipe Liners, Meihuan Zhu

Doctoral Dissertations

Thin walled polymeric liners are often used to rehabilitate deteriorated pipe lines. The host pipes into which these liners are installed are typically assumed to be structurally sound, and the liner is only expected to carry the external pressure exerted by the groundwater. This external pressure will induce creep deformation and radial deflections that may eventually result in collapse of the liner within the host pipe. The aim of this work is use computational modeling to better understand the evolution of conditions leading up to collapse so that improved liner design models can be developed. Emphasis is placed on a …

Finite Element Simulation Of Creep Buckling Of Cipp Liners Under External Pressure, Qiang Zhao

Doctoral Dissertations

The problem of long-term structural behavior of CIPP liners under external hydrostatic pressure has been characterized as a structural instability problem which is induced by time-dependent material deformation or creep. It is also a contact problem since the liner deflection is externally constrained by the host pipe. The intrinsically nonlinear problem is investigated by means of finite element simulation, with emphases on (a) the essential structural behaviors and mechanisms of buckling, and (b) the influences of inelastic material properties (i.e. yield strengths and creep rates) and geometrical parameters on liner's buckling resistance.

A liner first deforms as a free pipe …