Force on Pipe Under Bridge from Water Flow in River

[Coman]

I have a (suggested) 150 (6&quotdia steel pipe supported at 6m (20')spacing from the bridge piles across a stream. The water will cover the pipe at flood time by about 1m (say 3'). How do I calculate the loading on the pipe for a structural check of the pipe and its supports. Stream peak flow 3m/s (10'/s)

 

[Qshake]

Please give more information. Typically, the utilities are placed within interior girders for slab and girder bridges in order to mitigate the forces due to stream flow or impact from vehicle collision. Otherwise they are placed on the overhang.

As you can see we need to know where the pipe is located in order to be able to help.

 

[dik]

I'll reply in a little greater depth, later... but the biggest concern, off the top, would be the impact of water borne debris. Must run...

 

[Coman]

More Info - The bridge is timber pile, Concrete abutment, timber deck - 3 span. Overall Depth water course bed to under side of bridge 4m (12.3'). Pipe located 1m down from deck. Location of pipe non negotiable.

 

[dicksewerrat]

Does the stream freeze? Ice jam may tear out the pipe and the extra strain on the bridge may cause the bridge to fail.
What's in the pipe?

 

[dik]

There should be a mechanical/hydraulics engineer that can calculate the actual force of the water given the peak flow rate. The force should include for debris that 'hangs' on a pipe (weeds draping over it). The maxumum force, however, will likely be generated by the impact of an object floating in the water during flood periods.

Having said that, there are several other issues:

Is it possible to protect the pipe from flotsam?
Will the pipe accumulate debris (grass, weeds, etc.) that will increase the drag?
What does the pipe carry? Anything environmentally unfriendly?
What is the coating system for corrosion? abrasion?
Does it require special markings or colour?
Is it a problem if it breaks?
What authorities are involved?
How is it spliced?
How is it attached at shore? Can the connection flex?
I suspect that with 6" steel that bouyancy is not an issue.
Does it require a barrier to prevent rats or people from using it?
Should it be electrically isolated?

 

[Coman]

Too much erroneous information asked for people. This is in Western australia - no ice. The pipe carries a poly pipe getting water from a dam at a local winery. dont worry too much about debris, I will factor this in when I have a ball park number. if I can get this done who knows maybe the owner will reward me with a case of his best red. What i really want is UDL on the pipe.
Thanks so far but nothing yet usable

 

[kvram]

Dear Mr. Coman,
As pipe will be in water during flood time, calculate the horizontal and vertical forces acting on it at peak flow. Procedure as below.
Vertical forces: Self weight of pipe, water load in the pipe and water head above pipe during flood . Add for surge loads or wave forces.
Horizontal forces: For a circular cross section take a factor as 0.95( Ref. ASCE 7/98 page 61, assuning it is immersed in Fluid) ). Work out the pressures at top and bottom elevations of pipe with respect to Max Flood level . Since it is a flood water, take a suitable density value for water ( Assuming with lot of debris and impact value).
With this both vertical and horizontal simaltaneous load applications ,design your pipe section and conections.
Hope this may help you.

Ram