| Summary: | 碩士 === 國立成功大學 === 水利及海洋工程學系 === 87 === Bridge become partially or totally submerged during large floods are subjectto pressure-flow scour. Under this flow
condition, the velocity and bed scour at the bridge deck are much larger than that under non-pressure situations. In order to understanding the contraction scour at the bridge deck under pressurized flow condition, the first course is to analyze velocity and discharge flowing through the bridge deck.
The experiments were conducted to study the flow field, discharge, and water level at the bridge deck under the pressurized flow condition. A model bridge deck was tested under a variety of controlled pressurized flow conditions, and the experimental data were all recorded.
The experimental data were substituted into energy equation and continuity equation to calculate energy loss, energy loss coefficient. An equation to evaluated flow discharge related the energy loss was derived. The deviation from actual discharge and calculated discharge were within 10％.
The velocity data were compared with the log-law velocity distribution to predict the fore influence region (FIR) and behind influence region (BIR). The result showed that when the upstream Fround No. was smaller than 0.1 and the contraction ratio was smaller than 0.267, the maximum FIR would be within one quarter width of the bridge deck and the BIR would be within 4.7 width of the bridge deck.
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