Restrained Pipe Schedule

[EngWade]

I'm working on a Project where the town code is updating, and subsequently replacing all thrust blocking with restrained joints. I've done a fair amount of research on the subject, and found DIPRA's Thrust Restraint Design for Ductile Iron Pipe (and their free program) to be the best resource. Anyone who has also gone through this process, I'm sure, is well aware of how many factors go into the number of restrained joints required at various fittings/bends. So my question, does anybody have (or know of) a chart or schedule that spells this out pretty well that I could modify to fit my particular site? I'm just trying to save a little time on my end since this project was handed to me with a small budget.

As always, thanks for all the input.

 

[coloeng]

You will probably need to develop your own table/tables. The town will need to make some decisions that will make a table of mechanical restraints useable under the many diverse conditions that can occur, such as:
1) What factor of safety do they want to use.
2) Are they going to or do they require a certain type of pipe bedding and backfill and religiously follow the requirement. If they don't the table should be designed based on the worst case trench conditions.
3) What range of pipe diameters are typical for the town.
4) Decide if you want to base your table on one maximum pressure or have different tables with values for different pressures and pipe diameters.
5) Each different fitting configuration would need to have a separate table/tables.
6) The table would need to explain the assumptions that were used so that they could be modified if necessary.

There is probably other things that need to be considered, but that is what I thought of at the moment.

Personally, I think the town is being short sighted. Thrust blocking can be an inexpensive and reliable method for handling thrust without major complications. Mechanical restraint has its place in a system, but so does concrete.

 

[rconner]

Coloeng makes some good points. I am not sure I know exactly what you wish the schedule to show. All of the ”parameters” input into the DIPRA thrust restraint program of course have at least some effect on the required length of restraint that is output for the specific thrust focus involved (otherwise they would be “constants” in the program). However, if you have some relatively constant parameters across a particular job or utility (for example the same pipe size, soil type(s), trench type, required minimum depth of cover for a pressure pipeline that most follows the natural ground, and required thrust restraint design or test pressure etc., I guess it would more possible to craft a simple readable table of sorts that in plans or specifications etc. may be helpful to the Contractor or Inspectors etc. of that job. This could perhaps be done in different fashions e.g. simply by inputting that set of common parameters repeatedly into the DIPRA program, and then entering the results in cells of a spreadsheet table like ExCel (I don’t think that would take much time), or it could be done by actually inputting the various sub-formulas and final restrained length program using the calculating/equation abilities of such modern spreadsheet programs into a custom spreadsheet that would allow you to change whatever parameters you wish, for even some varying jobs or locales, and have it print out the table showing only what you wish. The latter would obviously take more time to develop. In any case I guess if you were to include such a table in a set of plans and specs, I do agree it should probably be appropriately footnoted with the known or assumed parameters involved, to avoid it being picked up e.g. by other folks in your firm or the utility and inadvertently applied to substantially different circumstances. All this being said, I guess it is possible you may find that some level of varying parameters doesn’t result in a whole lot of difference in required restrained lengths for some of your most common installations.

I believe the first versions of the DIPRA hard-copy thrust restraint manual (as early as 1984, and before the availability of the computer programs and downloads of same), incidentally did actually include several pages separated by soil type of required minimum restrained lengths of poly-wrapped and non-polywrapped restrained joint ductile iron pipe, for different depths of cover in increments up to 10 feet for the various soils and 90 degree horizontal bends at 100 psi. The user of these tables could then easily calculate the required restrained length for any other pressure or horizontal bend angles by a direct pressure ratio multiplier, and a separate trigonometric multiplier due to the varying bend angle. As these already voluminous tables just covered horizontal bends and did not include other thrust foci common to many jobs (such as tee branches, dead ends, vertical up bends, vertical down bends, reducers, etc.) that were however later rather easily output by the computer programs, I guess they were eventually done away with. Nevertheless, if you wanted those tables maybe photocopies of same could be provided by DIPRA or they could be contacted for better advice?