Browsing by Author "Dr. Jay Tu, Committee Member"

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    The Impact of Load History on Deformation Limit States for the Displacement-Based Seismic Design of RC Moment Frame Buildings
    (2008-10-22) Vidot-Vega, Aidcer Linalynn; Dr. Jay Tu, Committee Member; Dr. Mervyn Kowalsky, Committee Chair; Dr. Tasnim Hassan, Committee Member; Dr. James Nau, Committee Member
    The main goals of this research were (1) to study the relationships between material strain and deformation parameters such as curvature and drift for reinforced concrete moment frame structures and (2) to identify the load history effects on these relationships. Through the use of moment-curvature analyses, trends between strain and curvature for rectangular reinforced concrete sections were explored. Curvature-strain relationships that depend on axial load ratio and longitudinal steel ratio were developed from the moment-curvature analyses results. The curvature expressions were subsequently used to develop equations to compute interstorey drift based on strain limits for RC moment frames. The resultant equations can be used in performance-based design approaches such as direct displacement-based seismic design to compute target drifts and system displacements for prescribed limit states based on material strains. The interstorey drift equations were correlated against 54 frame building analyses using OpenSees with reasonable accuracy. To study the load history effects in the relationship between material strains and drift, the research was divided in two phases. The first phase considered RC column members subjected to symmetrical and asymmetrical cyclic reverse loading and seismic acceleration time histories. Column members with 2% and 4% longitudinal steel ratio and axial load ratio of 5% to 20% were analyzed. The second phase considered moment frame buildings subjected to seismic acceleration time histories. A total of five different moment frame models were analyzed. All the results were compared to monotonic (pushover) analyses. It was concluded that monotonic section analyses can be used to describe the envelope of seismic response since the relationship between strains and displacements/drift is minimally affected by different loading histories. It was also determined that a simple addition of the growth steel strain to the flexural tension strain is not correct, as previously thought.
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    An Integrated Approach to Lubricant Development in Cold Forging
    (2008-05-04) Karkhanis, Nikhil Sudhakar; Dr. Jay Tu, Committee Member; Dr. Jeffrey Eischen, Committee Member; Dr. Gracious Ngaile, Committee Chair
    Lubrication plays a very important role in the metal forming industry. Almost every metal forming process requires some form of lubrication or the other in order to obtain the desired component. Presently, various kinds of lubricants are being used in industry for different processes based on the lubricant properties and the process requirements. One of the primary objectives of this study is to establish a lubricant development methodology which is based on a thorough understanding of the lubrication mechanisms involved and the metal forming process itself. Evaluating the performance of a lubricant is an essential part of the development process. Various standard tribological tests employed in industry were used in this study. This involved both experimental and finite element analysis of the tests. Certain critical tribological parameters were identified for evaluating the performance of the lubricants and these were recorded for further analysis. Another important objective of this study is to develop a simulation databank which would contain the finite element simulations for the major forging components used in industry. The creation of this databank is an essential part of the proposed integrated approach to lubricant development. This databank will enable lubricant developers to optimize their product for particular forging applications. A case study was undertaken to prove the usefulness of the integrated approach. The new technique was applied to the development of a new polymer based environment friendly lubricant. The target process for this lubricant was tube drawing and hence it was necessary to get a lubricant with optimum properties for this process. The required performance parameters were identified through the critical tribo-mechanical parameters. Accordingly, the appropriate tribological tests were selected for lubricant evaluation. Initially, a set of eleven lubricant formulations were taken for testing, each with a slightly different chemical formulation. In order to narrow down the suitable lubricant formulation, a low severity friction test such as the ring test was performed. Once the better performing formulations were identified, a more severe friction test was employed to narrow down on the best possible lubricant formulation. During the entire process, the lubricant developer modified the chemical formulations slightly based on the test results. The result of this was improved performance in the lubricants.