Browsing by Author "Galambos, Theodore V."

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    Incorporation of Reliability in Minnesota Mechanistic-Empirical Pavement Design
    (Minnesota Department of Transportation, 1999-07) Timm, David H.; Newcomb, David E.; Birgisson, Bjom; Galambos, Theodore V.
    This report documents the research that incorporated reliability analysis into the existing mechanistic-empirical (M-E) flexible pavement design method for Minnesota. Reliability in pavement design increases the probability that a pavement structure will perform as intended for the duration of its design life. The report includes a comprehensive literature review of the state-of-the-art research. The Minnesota Road Research Project (Mn/ROAD) served as the primary source of data, in addition to the literature review. This research quantified the variability of each pavement design input and developed a rational method of incorporating reliability analysis into the M-E procedure through Monte Carlo simulation. Researchers adapted the existing computer program, ROADENT, to allow the designer to perform reliability analysis for fatigue and rutting. A sensitivity analysis, using ROADENT, identified the input parameters with the greatest influence on design reliability. Comparison designs were performed to check ROADENT against the 1993 AASHTO guide and the existing Minnesota granular equivalency methods. Those comparisons showed that ROADENT produced very similar design values for rutting. However, data suggests that the fatigue performance equation will require further modification to accurately predict fatigue reliability.
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    Monitoring and Assessment Program for Wabasha County Bridge
    (1998-09) Fick, Damon R.; Schultz, Arturo E.; Bergson, Paul M.; Galambos, Theodore V.
    A 143-m (470-foot) span steel truss bridge, the Wabasha County Bridge crosses the Mississippi River at Wabasha, Minn. In November 1996, the Minnesota Department of Transportation (Mn/DOT) implemented a retrofit strategy to mitigate perceptible vibrations in several truss members at moderate and strong wind gusts. In this strategy, Mn/DOT installed a "central cord" of tubular members, halfway between top and bottom cords, to reduce the effective length of the truss members, thereby increasing the natural frequencies of vibration and reducing the amplitude of vibration and the associated strains. This report documents the monitoring and assessment program used to investigate the dynamic response and efficacy of the retrofit strategy for the Wabasha Country Bridge. Researchers determined amplitudes and frequencies of the vibration for the longest diagonal member. The measured frequencies are larger than those estimated before the retrofit and have resulted in reduced strains and displacements from vibration. Maximum strain levels at the quarter point of the member are estimated to be small after the retrofit, with peak values corresponding to 8.6 MPa (1.2 ksi).
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    Stresses in Steel Curved Girder Bridges
    (Minnesota Department of Transportation, 1996-08) Galambos, Theodore V.; Hajjar, Jerome F.; Leon, Roberto T.; Huang, Wen-Hsen; Pulver, Brian E.; Rudie, Brian J.
    Steel curved I-girder bridge systems may be more susceptible to instability during construction than bridges constructed of straight I-girders. The primary goal of this project is to study the behavior of the steel superstructure of curved steel Igirder bridge systems during all phases of construction, and to ascertain whether the linear elastic analysis software used by Mn/DOT during the design process represents well the actual stresses in the bridge. Sixty vibrating wire strain gages were applied to a two-span, four-girder bridge, and the resulting stresses and deflections were compared to computational results for the full construction sequence of the bridge. The computational results from the Mn/DOT analysis software were first shown to compare well with results from a program developed specifically for this project (called the "UM program"), since the latter permits more detailed specification of actual loading conditions on the bridge during construction. The UM program, in turn, correlated well with the field measurements, especially for the primary flexural stresses. Warping stresses induced in the girders, and the stresses in the crossframes, were more erratic, but showed reasonable correlation. It is concluded that Mn/DOT's analysis software captures the behavior well for these types of curved girder bridge systems, and that the stresses in these bridges may be relatively low if their design is controlled largely by stiffness.