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srakumar

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Registered: 13/01/2009

Multiple Arch Bridges
What is the best unit to model the multiple arch bridges with different pier widths in between (i.e arch eyes spacing varies) and the shape of the arch changes too i.e smaller arches in the end.

Arch Unit or USBPR unit? Help does not clearly give on when to go for which unit? Any clear guidelines on which unit is more appropriate?

04/11/2009 15:23

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adamsk

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Hi Sravan,
My rule of thumb is: small, arched bridges - use ARCH; large, flat bridges - use USBPR. This is largely based on the research that was used to derive the formulae - the ARCH unit came from the HR "Afflux at Arch Bridges" report, based on UK bridges; the USBPR came from the US Bureau of Public Roads and mainly concerned typical US road bridges.
Others may have more practical reasons for choosing their preference.
NB USBPR does have the facility to model pier effects specifically.
Konrad

05/11/2009 09:44

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srakumar

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Konrad,

Thanks. It was a specific issue for the multiple arch bridges. Some times the no of arches are upto 10 in some old bridges.Choice of unit is not clear in the ISIS help. Any more light?

Sravan

09/11/2009 11:44

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MattH

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Sravan

The recommendation is that a for a single arch bridge unit representing multiple arches, the arches must act as a single unit - i.e. have similar velocities and water levels.

If the arches are very different sizes, then a better approach is to model as multiple units. As an example, I've modelled bridges with a number of arches in the channel as one unit, and the smaller flood relief arches on the floodplain as another arch bridge unit in parallel.

It's a matter of judgement how many units are needed, based on how you expect the hydraulics to behave.

Hope this helps

Matt

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Halcrow

18/11/2009 09:56

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