Applying bridge skew and pier angle

[Chris]

Hi-I have a bridge with a 100′ opening, 55′ width, and four sets of 1.5′ piers. However, when I apply a 20-degree skew to the bridge and piers, it significantly blocks the conveyance. I am confident that the angle of flow and bridge is correct, and my hand calculations support the blockage. This situation seems counterintuitive since many documents suggest that the flow turns inside the bridge, thus reducing blockage.

Is it recommended that I decrease the skew angle to address the blockage issue? I appreciate any advice you can provide regarding this issue.

Thank you for your time and help.

[Luis Partida]

Hi Chris, is this as steady state or unsteady state simulation? 1D or 2D or coupld?

The first thing I would do is remove the piers and run the model again to see if the problem still occurs. Also, I would check your internal XS’s.

[Chris]

It is a simple 1-D model, steady state.
The model has no problem and removing piers doesn’t answer my question.
Here is the hand calcs:
Skewed weir width = W x Cos(20)+L x Sin (20)=1.5 x 0.94 + 55 x 0.34 = 20.11
w=width of pier
L = length of pier which is the same as bridge width

I have 4 piers and the total skewed pier width is about 88′. This length obstruct about 80% of my flow conveyance. The model shows almost the same thing. The question is that is this realistic? Should I not skew the piers

[Author]

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