ASSESSMENT OF LIVE LOAD DEFLECTIONS IN A SIMPLE SPAN COMPOSITE BRIGDE WITH PRESTRESSED PRECAST CONCRETE GIRDERS
Date of Award
Master of Science
Hsiao, J. Kent
The purpose of this study is to investigate how accurately the distribution factor method estimates the live load deflections under the principles of the 2012 AASHTO LRFD Bridge Design Specifications (AASHTO LRFD specifications) compared to the results of the NISA finite element analysis software. The simple span bridge model analyzed is developed very similarly to the design example of the PCI Bridge Design Manual. The main difference is a shorter span length and smaller AASHTO-PCI bulb tee sections. Three main finite element models are created to estimate the live load deflections under the recommended live load conditions as per AASHTO LRFD specifications. The first model is simulated with simple support conditions. The purpose of this model is two-fold: compare the deflections to the distribution factor method and to the deflections of the second model that is simulated with elastomeric steel reinforced bearing pads. Thus, the stiffnesses of the elastomeric bearing pads of the second model are varied within the AASHTO LRFD specifications acceptable limits and under low temperature conditions the stiffness is increased accordingly for two cases. The purpose is to investigate if the stiffness have any significant affect on the deflections of the girders. Then a third model is created to investigate if the removal of the intermediate diaphragms have any affect on the deflections. The results of the first and second models, including the models with the allowed varied stiffnesses of the bearing pads, found only the interior girders deflecting up to 4% more and the exterior girders were deflecting up to 5.55% less than the estimates of the distribution factor method. In the case when the diaphragms are removed, the deflections of the inner most interior girders are deflecting up to 10.85% more compared to the same girders of the model which includes the intermediate diaphragms and the bearing pads. In the unique case of the second model where the bearing pads may stiffen significantly under low temperatures, the girders are deflecting up to 23% less than when at room temperature conditions. All these findings and other summarized results are discussed in greater detail in this study.
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