Doctor of Philosophy, University of Akron, 2015, Civil Engineering

A total of thirty samples of A36 structural “T” were tested under fatigue loading. Of the thirty, ten samples were tested under panting fatigue conditions. At a constant amplitude of stress ratio 0.01, fatigue tests were conducted under axial, combined axial and bending and pure bending conditions. Test data for a predefined stress range (Sre) and number of cycles to failure from the specimens were used to construct the stress range vs. life (S-N) curves for these structural welded “T”s. Differences were observed and noted in the individual S-N curves as well as in the combined S-N curves. Comparison of the S-N curves provided an indication of a suitable design resistance for these welded details. Fatigue design classification systems need to implement this classification for panting conditions, and design provisions are recommended. After testing, fatigue cracks were exposed and examined in a scanning electron microscope (SEM) to study the crack initiation and crack growth kinetics as well as the characteristics features that governed the observed fatigue behavior. The use of stress range as the primary fatigue strength parameter is a direct consequence of the role of residual stresses in the welded details and affects the S-N curves and is reflected in the use of the stress range and influences the slope as compared to typical design S-N curves. In order to understand the residual stresses and the effect on welded “T” fatigue behavior, two specimens were tested by the hole-drilling technique. Both the Power Series and the Integral Methods were employed for reducing the data. Resulting stress profiles and the general data trends were examined and compared for both cases and its effect on the S-N curves were discussed. Experiments were enriched with a Finite Element (FEA) study for axial, axial plus bending and pure bending specimens to numerically calculate the stress intensity factor (KI) in two dimensions as well as three dimensions. Stress intensity facto (open full item for complete abstract)

Committee: Craig Menzemer Dr. (Advisor); Anil Patnaik Dr. (Committee Member); David Roke Dr. (Committee Member); T.S. Srivatsan Dr. (Committee Member); Dmitry Golovaty Dr. (Committee Member) Subjects: Aerospace Engineering; Civil Engineering; Engineering; Materials Science; Mathematics; Mechanical Engineering

MS, University of Cincinnati, 2014, Engineering and Applied Science: Civil Engineering

Coupled core wall systems with steel coupling beams are effective seismic force resisting systems to resist structural collapse. A typical coupling beam shear wall system would dissipate energy through the formation of plastic hinges at the coupling beam-wall interface. These plastic hinges would damage the coupling beam, requiring an infeasible and uneconomical repair involving the replacement of the beam embedded in the concrete wall pier. However, research at the University of Cincinnati has introduced a weak-link section (the fuse) at the mid-span of the coupling beam that will dissipate energy through shear yielding, leading to the development and modification of the steel fuse coupling beams. This would allow the plasticity at the face of the wall to be shifted to the mid-span of the coupling beam, requiring a feasible and economical repair involving only the replacement of the fuse at mid-span.

Committee: Gian Rassati Ph.D. (Committee Chair); Thomas Baseheart Ph.D. (Committee Member); James Swanson Ph.D. (Committee Member) Subjects: Civil Engineering

PhD, University of Cincinnati, 2011, Medicine: Developmental Biology

Primordial germ cells (PGCs) are the embryonic precursors of adult gametes. In the mouse, they arise around E7.5 in the allantois, and migrate through the developing hindgut and midline dorsal body wall mesenchyme to colonize the gonad primordia by E11.5. PGC behavior, including proliferation, survival, and motility, is controlled by cellular signaling during migration. Steel factor is known as an essential survival factor for PGCs. It is the protein product of the Steel locus, and the ligand for the receptor tyrosine kinase c-kit, which is expressed by PGCs throughout migration. Steel factor exists in two forms, membrane-bound and the soluble, generated by alternative splicing. This thesis addresses two general questions: 1) Is PGC behavior controlled by Steel factor from the beginning of their migration? 2) Do the two different forms of Steel factor control different aspects of PGC behavior? Using the mouse reporter line Stella-GFP, in which PGCs express GFP under the control of the promoter of Stella gene, I demonstrate that PGC number is significantly reduced in Steel-/- embryos at E7.5. Similarly, in the absence of Steel factor, either by null mutation or antibody blockade, PGCs aggregate together and show dramatically decreased motility, but their directionality is maintained. These data indicate an essential role for Steel factor in PGC survival and motility. I then show that Steel factor-expressing cells surround PGCs from the time of their initial specification in the allantois, to the time of their colonization of the gonad primordia, providing a “spatio-temporal niche” that travels with PGCs to regulate their survival, proliferation and motility throughout migration. Further, I show that these functions of Steel factor in PGC behavior are distributed between the membrane-bound and soluble forms by analyzing PGC behavior in Steel-dickie mutant embryos, which make only the soluble form. Soluble Steel factor alone is sufficient for PGC survival at E7.5. How (open full item for complete abstract)

Committee: Christopher Wylie PhD (Committee Chair); Aaron Zorn PhD (Committee Member); Kenneth Campbell PhD (Committee Member); Iain Cartwright PhD (Committee Member); James Wells PhD (Committee Member) Subjects: Developmental Biology