Browsing by Author "Mervyn Kowalsky, Committee Member"

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Behavior of High-Strength Concrete Members Subjected to Combined Flexure and Axial Compression Loadings
(2006-12-08) Mertol, Halit Cenan; Amir Mirmiran, Committee Member; Paul Zia, Committee Member; Sami Rizkalla, Committee Chair; Mervyn Kowalsky, Committee Member
The use of high-strength concrete (HSC) in structures and bridges has become a common practice worldwide. In bridges, HSC could lead to a reduction in number and depth of the girders as well as an increase in the span length. These features reduce the complexity of a project with reduced number of piers, construction time and cost. Furthermore, the enhanced durability of HSC could result in reduction of the maintenance costs and increase the service life of the structure. In buildings, the sizes of the members could be significantly reduced which could help in the design and construction of higher structures with larger spans. However, due to lack of research data, most of the design codes worldwide limit the applicability of HSC. A total of 21 plain concrete specimens were tested under combined flexure and axial compression to evaluate the stress-strain distribution of HSC in the compression zone of flexural members. The variables considered in this investigation were mainly the strength of concrete and the age of the specimen. The measured stress-strain curves and stress block parameters, including the influence of the concrete strength, were compiled with the data in the literature to evaluate the fundamental characteristics of high-strength concrete in the compression zone of flexural members. A total of 42 cylindrical specimens and 18 prism specimens were used to evaluate the creep and shrinkage properties of HSC. The variables considered in this investigation were the concrete compressive strength, specimen size, curing type, age of concrete at loading and loading stress level. The creep coefficients and shrinkage strains were obtained for the range of concrete compressive strength, evaluated and compiled with the current predictions according to the design codes. Using the test results of this research and other researches in literature, revisions to the LRFD Bridge Design Specifications (2004) are recommended to extend the applicability of its compressive and combined compressive and flexural design provisions to concrete compressive strengths up to 18 ksi.
Characterization of High-Strength Bolt Behavior in Bolted Moment Connections
(2007-09-19) Wade, Patrick Michael; Mervyn Kowalsky, Committee Member; James Nau, Committee Member; Emmett Sumner, Committee Chair
Experimental Testing of Unreinforced Masonry Walls Strengthened with Orthogonal Near-Surface Mounted CFRP Subjected to Out-of-Plane Loading
(2009-08-05) Wylie, John Curtis; Rudolf Seracino, Committee Chair; Emmett Sumner, Committee Member; Mervyn Kowalsky, Committee Member
Unreinforced masonry (URM) structures comprise a considerable proportion of the building stock worldwide. However, these structures generally do not behave well under extreme wind or earthquake loading. As part of on-going research, methods of repairing or strengthening URM walls subject to out-of-plane loading using fiber-reinforced polymers (FRP) are being investigated. For several reasons, one method showing particular promise is the use of near-surface mounted (NSM) Carbon FRP strips. Research to-date has made significant progress in quantifying the fundamental behavior of the bonded FRP-to-masonry interface and the behavior of URM walls repaired with vertical FRP strips subject to out-of-plane loading. This thesis presents the experimental results of five large-scale clay brick masonry walls strengthened using NSM CFRP strips and loaded out-of-plane statically to failure using an airbag system. Vertical and Horizontal NSM configurations were tested separately as well as orthogonal grid configurations constructed using two different techniques. The experimentally observed failure mechanisms are described in detail for each wall.
Finite Element Modeling of Light Frame Wood Structures An Integrated Approach
(2009-06-26) Collins, Michael Scott; Bohumil Kasal, Committee Chair; Mervyn Kowalsky, Committee Member; Jim Nau, Committee Member; Vernon Matzen, Committee Member
This research aims to improve the framework and practicality for the analysis and design of light frame wood structures. The light frame wood structure is broken down into its constituent components for modeling: connections, shearwalls and diaphragms, then the assembled structure. This work relies extensively on available finite element technologies to identify key components and modeling methods of those key components. Finite element modeling strategies were developed to investigate the response of light framed wood structures. The models developed are intended to be general in nature and not restricted to a particular type of loading and cover static monotonic, dynamic monotonic, static cyclic and dynamic loading. In doing so, modeling strategies are proposed to make the models more computationally efficient and reduce the complexity without a loss of information of the response. Experiments were conducted on connections, components, and the assembled structure and designed to evaluate the response of wood structures and their components and verify the developed models. Criteria used to evaluate the models include hysteresis shape, energy dissipation, strains, local displacements and forces, and observed failure modes. and compared with results of experiments designed and verify the model.