Rising Main Thrust Block

[anyoldnick2014]

Hi,

I'm completely new to eng-tips as well as completely new to designing rising mains so I'm on here looking for advice.

If bends in my rising main are, what I consider, a fairly large radius (in this case 4m) do I still need to include thrust blocks? If so is there a rule of thumb radius at which thrust blocks are no longer needed?

Thanks in advance, all help appreciated.

 

[LittleInch]

If your pipe is not welded then yes, IMO you need to include. If it's welded then you shouldn't need to.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[gerhardl]

I have seen much more missing thrust-blocks and supports than too many, actually zero of the last category. . Of course there is a limit somewhere, at least mathematical. 4 m could under cisrcumstances be neglectible, and 400m radius certainly is.

There will always be more or less forces to support, deending on pipeline size. Forces might occur from flow. weight, acceleration, and unexpected situations under filling and emtying,waterhammer, larger temperature changes and possible breakdown of pipeline other places.

A thrust block too many will do no damage, but will of course cost, so you ought to calculate. Your situation may differ from 'standard'.

PS: Note special rules for HDPE pipelines wich will require less to none thrust support under normal water- main conditions.

I hope others can help you more directly!

 

[cvg]

For ductile iron or pvc pipe - mechanical / restrained joints are recommended. You can use fusion welded HDPE pipe.

I would assume that you are not likely using weldable steel pipe for a sewer forcemain.

 

[anyoldnick2014]

Thanks everyone for your responses.

To clarify, the rising main in question is 160mm diameter HDPE and will be carrying foul sewage. Site constraints mean large radii (20, 30, 40m etc.) are out of the question, therefore leading me to think thrust blocks are definitely needed. In which case I reckon I'm better off using short radius bends as, from my basic understanding, it should need a smaller area of concrete to support the smaller bend and resist forces? Does this sound right?

Thanks in advance.
anyoldnick2014

 

[LittleInch]

Why do YOU think you need thrust blocks?

Are these bends horizontal or vertical (not that it makes much difference)

Thrust blocks only exist in water piping systems to hold together push fit low pressure Cast Iron or PVC pipes. You need thrust blocks in these systems at every change of direction to stop the system pushing itself apart under end cap loading as the axial strength of the pipe joints are virtually zero. If you have a welded system, be it PE or steel, thrust blocks are a complete waste of time and money as they do absolutely nothing but can actually cause problems due to locking in stresses which could be relieved by a few mm of movement at the bends.

Just make sure you compact the soil around the pipe properly and you're home and dry. The continuous support and soil pressure will hold your pipe in position without a problem. No other pipeline systems other than those using push fit joints use thrust blocks unless the designer has come from the water industry and thinks that all pipelines need them - they don't.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way