Thrust Block Design 2

[mtroche]

I need information about the thrust block design procedure. In one side I have the momentum formula, and in the other side I have this formula T=2PAsin(phi) where “P” is the pressure, “A” is the pipe cross section area where the flow goes, and “phi” is the bend angle. Is the last formula a "rule of thumb" for the thrust block design? Using this formula, an engineer calculated 10 concrete trucks to build a thrust block for a 45 degrees, 48inches, vertical bend, and using the momentum formula I get only 2 concrete trucks for the vertical thrust block. The pressure (P) that he used was an assumed value equal to two times the working pressure for this pipeline. The working pressure for this pipeline is 150psi. So, at the end, the engineer is multiplying the working pressure by four!!

I know... I know. To design a Thrust Block I have to use the momentum formula and take in account the weight of the bend itself and the water inside the bend if it's a vertical thrust block, but I am a little confused with the engineer using that formula.

I'll be grateful if someone of you show me an example on how to design a vertical and horizontal thrust block.

Thank you for your information.

 

[butelja]

The formula is for hydrostatic pressure. While momentum effects are present, they are normally orders of magnitude smaller that the pressure thrust.

 

[whymrg]

Check

http://dmz1.mwwssb.com/mwwssb/whatwedo/dept/engineering/details.shtml

for Thrust Block Details by Montgomery Water Works and Sanitary Sewer Board. It might help

 

[Ginger]

Suggest you look at CIRIA

http://www.ciria.org.uk

They have produced a report which shows how to design thrust blocks in varying types of ground and includes good practical advice on detailing and construction Andy Machon

 

[mtroche]

Ginger

Your answer to my request looks good, but where exactly can I get the information in the CIRIA's website?

ATT: Michael Troche, P.E.

 

[Ginger]

I think you need to buy the report from CIRIA

Andy Machon