Thrust Blocks Dimensions 3

[Lash2680]

I found several programs on-line to use calculating the force and surface area for buried pipeline thrust blocks. I cannot find a program which will calculate thrust block dimensions which do not envelope the pipeline into the thrust block. I need to design the thrust block positioned to the side of the pipeline. Any suggestions? Thanks.

 

[msquared48]

Do it by hand...

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[EngineerofSteel]

If you position it "to the side", which must mean behind and below the turn (yes?), how will you prevent lateral movement?

 

[csd72]

lash2680,

This is one of those cases where if you need a computer to do the calculations for you then you probably shouldnt be doing it.

It is a really simply case of statics.

To calculate the load to be resisted you need to add the force vectors of the fluid pressure and the flow velocity as well as any additional loads from valve closure e.t.c.

Once you have this force then calculate tha average passive resistance pressure of the soil at mid height of the pipe and divide by the appropriate safety factor.

The required lateral bearing area is the force divided by the average bearing area. The rest is just checking that you have sufficient plain concrete to spread the load.

 

[msquared48]

Like I said, do it by hand. It's a five minute problem.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[rconner]

The guidance with regard to thrust blocks you can download from

http://dipra.org/pdf/thrustRestraint.pdf

may be of help (I believe it is the same as is avaialble in AWWA Manual M41).

 

[jgailla]

That DIPRA pdf is a good resource for thrust restraints. The last time I downloaded it (2010), however, there is a mistake in one of the equations that omits the diameter of the pipe in developing the thrust to be restrained.

 

[rconner]

Thanks, jgailla -- could you elaborate a little concerning the problem you reportedly found? I read the DIPRA manual, that I believe is in its sixth extensive hard-copy printing, was last revised in 2006 (when it said only editorial revisions were made). When I looked at a hard-copy of this 6th edition I had also downloaded and printed some time ago. I noticed the pipe diameter per se does not show up in the thrust block formula shown on page 5, but the pipe cross-sectional thrust area, “A” used to develop the resultant thrust does use this value (expressed in feet, it appears to three significant figures). With ductile iron pipe, the thrust area is thus based on the outside diameter of the pipe, as the outside of the spigot of the pipe can normally be pressurized nd potentially slide in piston-like fashion, within a gasket normally retained in a bell/socket gasket groove of such piping.

On page 20 of this manual I saw that area, “A” in turn is defined as 36 ? (D’)2 , when D’ is expressed in feet and the cross-sectional, “A” is desired in square inches (I guess to be compatible with pressure, normally expressed in pounds per square inch). As the resultant thrust on a horizontal bend is 2PAsin(?/2), the required thrust block dimension formula on page 5 thus appeared reasonably correct to me.

[I incidentally happened to have a copy of the original first edition DIPRA Thrust manual, dated 1984, and when I looked at that old manual, it appeared this original basic thrust block design presentation 27 years ago appeared to be basically the same, even back then.]

 

[jgailla]

rconner,
I went back and looked at the reference I had used. The references were actually a reprint of portions of the DIPRA manual and was called "Connections" by EBAA Iron. I would have to go through the reference in detail to spot the error, but I remember an issue with one of the equations when coding it into a spreadsheet. The equation omitted the diameter of the pipe. After another look at the EBAA publication, it seems likely that the publication misprinted the data from DIPRA.

 

[rconner]

[jgaila, thanks for tracking this down!]