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MariaN

Effect of more than 1 bridge side by side

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Hi

I have an aligment that is triplicated, this means we have 3 bridges one after the other one. Whe I introduce additonal form losses how do I consider the existence of 3 bridges? i am using form losses where the piers are going to be, and assuming the piers of all bridges are aligned, should I only consider higer losses but in one of the bridges and nothing for the others? or divide the add_form_loss in the 3 bridges?

Thanks for your help

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Maria,

The AustRoads publication "Waterway design - a guide to the hydraulic design of bridges, culverts and floodways" has a section "Effect of Dual Bridges" which you may want to read if you haven't already. But the duality (or in your case triplicate nature) is dependent on the embankment of each interfering with contraction and expansion of flow rather than on interacting pier turbulence losses. I think (and I stress it is only my thoughts) that you should apply the same additional form losses at each pier set at each bridge. And provided you have sufficient grid resolution, TUFLOW will handle the embankment interference in expansion and contraction in the 2D domain.

Tina

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Hi Maria

Yes, it would be worthwhile referring to the effect of dual bridges. Ultimately the losses will be dependent on whether the 1st bridge provides some shielding for the 2nd and/or 3rd bridges. If the bridges are close together and the piers are all aligned this will give a lesser afflux than if the bridges are further apart (giving enough distance for the streamlines to reform) and/or the piers are not aligned or are of different dimensions. The encroachment of any embankments will also be important, but as Tina says, provided a sufficiently fine grid is used to replicate the flow patterns around the embankments, the energy losses associated with the embankments should be reasonably well modelled by the 2D representation.

Sensitivity of different assumptions and comparison with publications such as Waterways Design and/or a HEC-RAS or similar model can be worthwhile when it comes to structures.

Cheers

Bill

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