Pipe restraint at Fire Water Lines
Pipe restraint at Fire Water Lines
(OP)
I have two existing buildings with dedicated fire services. For joints I have called out either flanged joints, mechanical joints or a combination of the two for restraint. I have also given the contractor the option to use thrust blocks with the appropriate sizes called out per plan.
Typically, I understand mechanical joints such as the EBBA Iron Megalug to allow you the transfer of thrust forces from the water to the megalug to the pipe where it gets transfer to the soil via friction between the pipe and the soil with no thurst block required. This would assume that you have enough length of pipe to develop the capacity due to friction to take on that transferred thrust force. Otherwise the force would get transferred to any thrust blocks. Since many of the pipe runs are relatively short in length, I have called out the use of mechanical joints in addition to the thrust blocks.
Am I been over conservative? The contractor would like to know as to why he can't just use push on joints with thrust blocks. By the way, fire lines are tested and are operated at higher pressures than domestic lines, therefore the extra factor of safety, in my opinion, can only be a good practice. Am I missing something? Your thoughts! Thank you.
Typically, I understand mechanical joints such as the EBBA Iron Megalug to allow you the transfer of thrust forces from the water to the megalug to the pipe where it gets transfer to the soil via friction between the pipe and the soil with no thurst block required. This would assume that you have enough length of pipe to develop the capacity due to friction to take on that transferred thrust force. Otherwise the force would get transferred to any thrust blocks. Since many of the pipe runs are relatively short in length, I have called out the use of mechanical joints in addition to the thrust blocks.
Am I been over conservative? The contractor would like to know as to why he can't just use push on joints with thrust blocks. By the way, fire lines are tested and are operated at higher pressures than domestic lines, therefore the extra factor of safety, in my opinion, can only be a good practice. Am I missing something? Your thoughts! Thank you.





RE: Pipe restraint at Fire Water Lines
RE: Pipe restraint at Fire Water Lines
RE: Pipe restraint at Fire Water Lines
Many of the agencies I deal with here in Northern CA require DIP with flanged fittings for certain components of the undergorund system. Like the post from rconner, I tend to call out flange joints for very short runs of assembly, say 2 to 5 feet on the average. Once it gets longer than that and if project specs and the agency allow it, I will use mechanical joints. I agree, flanged joints lack the flexibility but I wouldn't see that as issue on relatively short runs.
I also agree that the use and cost of megalug and thrust blocking greatly outweighs possible system failure.
Does anyone outer know of any data or studies related to thrust restraint by push-on joints alone?
RE: Pipe restraint at Fire Water Lines
On the other hand standard push-on or mechanical joint pipes that have only elastomeric gaskets but with no special adaptations can only be used in the midst of long, reasonably straight runs of pipes that are not subject to such large axial tensile forces. Also, fittings with similar push-on or mechanical joining ends and just elastomeric gaskets with no special adaptations or retainer glands etc. must also be thrust/concrete reaction-blocked in pressure piping applications. Push-on joint pipes or fittings with just rubber gaskets (no gripping metal teeth, or any other structural adaptations for restraint etc.) are thus generally considered to provide no dependable (at least tensile) axial thrust restraint.
To perhaps get a better feel for the subject, you might want to download e.g. the manual "Thrust Restraint Design for Ductile Iron Pipe" from dipra.org (that I think has been available for the last quarter century), and also perhaps visit vendors' sites that provide partial cross-sectional views of the many available joining configurations (e.g. http://www.acipco.com/adip/products/Sect2.pdf and portal http://www.acipco.com/adip/pipe/restrained/).
I guess I should probably clarify in light of a couple posts by others that I am in general also not promoting the contemporary use of flanged joints underground (I prefer instead some flexibility, or at least a little available "wiggle", for buried applications!)
RE: Pipe restraint at Fire Water Lines
Thank you for the valuable information. The intent of my previous question was to obtain possible data on any potential load capacity (if any) of the push on joint and gasket alone. More on the side of independent studies on the product itself, not intending to show confusion on my part or cause confusion for others.
On a different note, I have come across some manufacturers that claim that the use of their mechanical joints with their pantented products can eliminate the use of thrust blocks. I agree with you, thrust blocking should also be used to provide more dependable restraint.
Much of the work that our office has been producing with regards to these applications has been in deveoplemnt of Shop Drawings for contractors seeking to obtain approval and permits for the installation of fire lines. Believe or not I have had to battle agency offcials on requiring the use of thrust blocks in combination with flanged fittings. I supppose that is the other end of the spectrum in asking for way too much and not understanding how forces are distributed through different pipe applications.
RE: Pipe restraint at Fire Water Lines
As far as city officials goes, it seems that review of permits is always done by the youngest staff in the department. Rarely ever done by an engineer. All the older, experienced engineers are now being given retirement packages so that cities can balance their dwindling budgets. It's a huge brain drain which is leaving the cities (and the states) being run by a bunch of lower paid, inexperienced newbies.
RE: Pipe restraint at Fire Water Lines
1. Unrestrained joint pipes and/or also fittings (bends etc.) but with concrete reaction blocking (i.e. thrust blocks) buttressing any significant thrust foci (large angle bends).
2. Restrained joint pipes and fittings with no reaction blocking.
3. Systems employing all restrained joint pipes and fittings AND reaction blocking at the same time ("belt-and-suspenders.")
I am NOT advocating any one of these over the other for any specific local application; I feel to do so would imply I know more of local conditions (a great many variables could come into play) than I do!
Now, I will again say that IMHO you should not however expect significant axial tensile strength for pressure thrust restraint purposes at least for any high pressures and/or larger angle bends from only simple, unrestrained push-on joints like Carnegie joints for steel and pccp, stab joints for steel, standardized and unrestrained mechanical or push-on joints (like Tyton or Fastite) for ductile iron piping (but without retainer glands, or without embedded gripping teeth in gaskets etc.), nor say unmodified Reiber joints for pvc piping.
You should use instead special restrained joint adaptations (such as provided at link) when you are trying to restrain without thrust blocking any substantial bend angles in pressure piping.
RE: Pipe restraint at Fire Water Lines
RE: Pipe restraint at Fire Water Lines
I also design waterline thrust restraint "overly conservative" because it's my PE stamp on the plans and I feel more comfortable with a little more thrust restraint than a little less. For higher pressure and larger diameter lines, it becomes a public safety issue. I have never seen nor experienced a catastrophic watermain break but I don't want to either.
I have learned that, once in the field, the inspector and the contractor have scaled back some of my design based on their experience - not saying this is right or wrong, just saying how it goes around here. But I've never given them the go-ahead to do so and probably wouldn't.
If it were me, I'd make the hard stance and tell the contractor that the design you put on the plans is (a) the design you, as the engineer on record, have proposed for the given application and (b) is the design the contractor choose to accept at the time of bid. To deviate from the design could cause issues with local laws regarding government purchasing/procurement.
Good luck with your situation.