Browsing by Author "Michael L. Leming, Committee Member"

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Erection and Strength Aspects of the Roof Trusses for RDU Airport Terminal C Project
(2008-07-24) Zubillaga, Jose Antonio; David W. Johnston, Committee Chair; Emmett A. Sumner, Committee Member; Michael L. Leming, Committee Member
Lateral Pressures of Fresh Concrete on Wall Formwork under High Rates of Placement
(2005-11-10) O'Janpa, John Victor III; David W. Johnston, Committee Chair; James Nau, Committee Member; Michael L. Leming, Committee Member
Current ACI guidelines for the design of formwork contain equations for the prediction of the lateral pressure of concrete exerted on the form which consider the rate of vertical rise of the concrete in the form, the temperature of the concrete, and the effect of various admixtures. These equations contain limitations on the acceptable slump of the concrete and the maximum rate of vertical rise during placement. However, in an ever increasing effort to increase productivity in the construction field, many concrete contractors place concrete in wall forms under conditions that exceed the equation limitations. The focus of this study is to create a field measurement system that can be used by future researchers to accurately measure formwork pressures in a wide range of applications and to gain a better understanding of the lateral pressure behavior of fresh concrete. For the experiment, two different data collection systems were created, one utilizing center-hole load cells which could measure tension forces in a variety of form ties, and the other consisting of a group of pressure cells that can easily be screwed into many concrete form facings. A total of nine forms were instrumented in the field with some combination of this data collecting equipment and lateral pressures were monitored during the concrete placement. A lateral pressure distribution was plotted for each placement based on the field measurements, noting the rate of vertical rise, slump, and temperature of the concrete mixture. Measured pressures were then compared to those that would be predicted by various ACI and other equations ignoring the limitations on rate of placement, to test the applicability of those equations when the concrete is placed at very high rates.
Optimizing Roof Maintenance and Replacement Decisions
(2006-01-05) Al-ibrahim, Anwar Adel; Salah E. Elmaghraby, Committee Member; David W. Johnston, Committee Chair; John W. Baugh, Committee Member; Michael L. Leming, Committee Member
The objective of this research is to develop a Decision Support System that helps allocation of available funds to optimize roof maintenance strategies. The Decision Support System analyzes different maintenance alternatives available for each roof element and chooses the alternative that maximizes the benefits due to savings resulting from postponing element replacement. The analysis uses the Life-Cycle Cost to calculate the Reduction in Uniform Annual Cost (RUAC) that is used as the economical decision criterion to select the most economical maintenance alternative for each roof element at different condition states. The analysis utilizes integer linear programming to optimize the selection of maintenance actions for the different elements by maximizing the RUAC under budgetary constraints. Excel and AMPL software are used to implement the analysis. This study uses the roofing systems of 28 buildings on the North Carolina State University campus as a model to develop the Decision Support System. Parameters necessary to develop the model are estimated. The analysis is tested on the available data base.
Short-Term Material Properties of High-Strength Concrete
(2005-07-27) Logan, Andrew Thomas; Sami Rizkalla, Committee Member; Michael L. Leming, Committee Member; Amir Mirmiran, Committee Chair
The need to extend the applicability of the AASHTO LRFD Bridge Design Specifications to high-strength concrete is being addressed by a series of projects being sponsored by the National Cooperative Highway Research Program (NCHRP). Among these projects, NCHRP Project 12-64 is being carried out at North Carolina State University (NCSU) to expand the use of the design specifications to 18,000 psi (124 MPa) for reinforced and prestressed concrete members in flexure and compression. As a part of this project, specimens were tested to determine the material properties of three high-strength concrete mixtures having target compressive strengths of 10,000, 14,000, and 18,000 psi (69, 97, and 124 MPa). The effects of various curing methods were also studied. This study covers the compressive strength, elastic modulus, Poisson's ratio, and modulus of rupture of high-strength concrete. The study showed that extended curing beyond 7 days resulted in little or no increase in compressive strength. For predicting the elastic modulus of high-strength concrete, the ACI 318-02 or AASHTO-LRFD equation over-estimates the actual modulus while the ACI 363R-92 equation adequately predicts the measured value. The modulus of rupture equation in ACI 318-02 or AASHTO-LRFD gives a good approximation of the modulus of rupture of high-strength concrete when 1-day heat curing and 7-day moist curing are used. The equation from ACI 363R-92 gives a good estimate of modulus of rupture values for continually moist-cured specimens. The Poisson's ratio of high-strength concrete is generally within the range of that reported for normal-strength concrete.
A spatial Asset Management Study Through an Analysis of Pavement Marking Performance
(2008-06-22) Sitzabee, William E; William Rasdorf, Committee Co-Chair; Joeseph Hummer, Committee Co-Chair; Hugh A. Devine, Committee Member; Michael L. Leming, Committee Member