Study on Most Unfavorable Pier Position of Local Scour Around Parallel Bridges with Unequal Spans
In order to quickly locate the most unfavorable pier position of parallel bridges,the generalized model test combined with numerical simulation method is used for studying the influence of span combination and arrangement of two-column abutment parallel bridges on the most unfavorable pier position.The result shows that the most unfavorable pier position of local scour around parallel bridges is mainly distributed near the river center along the river width and concentrates in the first row of piers of each two bridges along the flow direction.The most unfavorable pier position of local scour depends on the relative layout of two bridges'arches.When the downstream pier is within the tail flow area of upstream pier,the most unfavorable pier position is at the upstream bridge.Conversely,when the downstream pier is in the accelerated flow area,the position occurs at the downstream bridge.In practical engineering,the geometric variable θ can be used as a key variable in determining the distribution of the most unfavorable scour positions of parallel bridges,and it also reflects the extent of the influence of wake zone of parallel bridge piers,thus indicating the method of determining the location of the most unfavorable pier position.After locating the distribution of the most unfavorable piers along the direction of flow and the width of river,the angle between the first row of two bridge piers and the incoming flow direction could be expressed.When the angle is less than 14°,the most unfavorable pier is located at the first row of piers of upstream bridge,conversely,it is located at the first row of piers of downstream bridge.The study result can provide reference and basis for the design,assessment and protection against flooding of parallel bridges with unequal spans.
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