Query about a bridge bent submerged in water 1

[Hassaan_16]

I am doing a case study on a two-span bridge for help in designing a similar one but in an area of high seismic activity. The case-study bridge is constructed on a controlled channel, lined with concrete, and with 10ft depth and 10ft/s stream velocity. The designer has provided a hefty skew of 32 degrees just so that the abutments and the bent are parallel to the water flow (Pictures attached). I think in these conditions where stream flow forces are so small and there is no danger of scouring between the bent piers, the bridge could have been designed without skewed bents and abutments. So, my question is: What could be the problems associated with the design if the bent and abutments were designed with a 0 degrees skew? Because in my view, the two problems i.e., stream flow pressure and scouring, associated with water flow are absent in this case.

 

[BridgeSmith]

10ft/s is not low velocity. It's actually rather high. Not only would your plan of a zero degree skew increase the potential for scour, increase the stream force on the pier, and decrease the cross-section of the channel, it also increases the required length of the bridge, in order to provide the specified channel width, which is measured perpendicular to the channel between the closest corners of the abutments.

In 20+ years of designing bridges, I've never employed a zero degree skewed bridge for a channel that's skewed 10 degrees or more.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[PEinc]

Good answer, BridgeSmith.

http://www.PeirceEngineering.com