Browsing by Subject "Modulus of elasticity"

Now showing 1 - 3 of 3
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    Mechanical Properties of High Strength Concrete
    (Minnesota Department of Transportation, 1998-01) Mokhtarzadeh, Alireza; French, Catherine E.
    Researchers conducted an experimental program to investigate production techniques and mechanical properties of high-strength concrete and to provide recommendations for using these concretes in manufacturing precast/prestressed bridge girders. High-strength concretes with 28-day compressive strengths in the range of 8,000 to 18,600 psi (55.2 to 128 MPa) were produced. Test variables included total amount and composition ofcementitious material, portland cement, fly ash, and silica fume; type and brand of cement; type of silica fume, dry densified and slurry; type and brand of high-range water-reducing admixture; type of aggregate; aggregate gradation; maximum aggregate size; and curing. Testing determined the effects of these variables on changes in compressive strength and modulus of elasticity over time, on splitting tensile strength, on modulus of rupture, on creep, on shrinkage, and on adsorption potential as an indirect indicator of permeability. The study also investigated the effects of test parameters such as mold size, mold material, and end condition. More than 6,300 specimens were cast from approximately 140 mixes over a period of three years.
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    Stress Wave Sorting of Red Maple Logs for Structural Quality
    (University of Minnesota Duluth, 2001-11) Brashaw, Brian K; Wang, Xiping; Vatalaro, Robert J
    Existing log grading procedures in the United States make only visual assessments of log quality. These procedures do not incorporate estimates of the modulus of elasticity (MOE) oflogs. It is questionable whether the visual grading procedures currently used for logs adequately assess the potential quality of structural products manufactured from them, especially those in which MOE is of primary concern. The purpose of this study was to investigate the use of stress wave nondestructive evaluation (NDE) techniques to sort red maple logs for the potential quality of lumber obtained from them. Twenty red maple logs were nondestructively evaluated using longitudinal stress wave techniques and sorted into four stress wave grades. The logs were then sawn into lumber. Finally, the lumber specimens were dried and graded a final time using longitudinal stress wave techniques. The results of this study showed that good relationships existed between stress wave times measured in logs and the lumber produced from the logs. It was found that log stress wave grades have a positive relationship with the lumber grades. Logs with high stress wave grades produced high grade lumber. These findings indicate that the longitudinal stress wave technique could be used in sawmills to sort logs/cants for the production of high MOE products.
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    Validation of Prestressed Concrete I-Beam Deflection and Camber Estimates
    (Minnesota Department of Transportation, 2012-06) O'Neill, Cullen; French, Catherine
    The camber at the time of bridge erection of prestressed concrete bridge girders predicted by the Minnesota Department of Transportation (MnDOT) was observed to often overestimate the measured cambers of girders erected at bridge sites in Minnesota, which, in some cases, was causing significant problems related to the formation of the bridge deck profile, the composite behavior of the girders and bridge deck, delays in construction and increased costs. Extensive historical data was collected from two precasting plants and MN counties and it was found that, on average, the measured cambers at release and erection were only 74% and 83.5%, respectively, of the design values. Through data collection, analysis, and material testing, it was found that the primary causes of the low camber at release were concrete release strengths that exceeded the design values, the use of an equation for concrete elastic modulus that greatly under-predicted the measured values, and thermal prestress losses not accounted for in design. Fourteen girders were instrumented and their camber measured and the program PBEAM was used to evaluate the influence of various time-dependent effects (i.e., solar radiation, relative humidity, concrete creep and shrinkage, length of cure and bunking/storage conditions) on long-term camber. Once investigated, these effects were included in long-term camber predictions that were used to create sets of both time-dependent and singlevalue camber multipliers. The use of these multipliers, along with modifications made to the elastic release camber calculations, greatly reduced the observed discrepancy between measured and design release and erection cambers.