Featured in Water Online's Case Studies

06/06/1997

Twenty Five Ton Dozer Outplayed in Joint Restraint Test

On April 11 of this year, in response to a common question the firm's personnel often are asked, EBAA Iron performed a convincing force demonstration of several of its pipe restraint products. This question usually is posed by a client after hydrostatic testing of the installed restraint devices has been carried out, and a typical example is: "OK! I believe that your restraint will hold 350 psi, but how much force will it hold'?"

It can be difficult to explain the direct correlation between dead-end thrust and internal pressure. This probably is because an observer can't "see" the force related to the pressure. The only indication is by a needle moving on a pressure gauge. The company has answered the question by trying to explain the situation with formulas, charts, and graphs. While such illustrations on paper give accurate indications of the magnitude of the forces involved, the concept is demonstrated much more effectively when presented in some visual manner.

The company normally pressure tests a 12-in. restraint to demonstrate the holding performance. The Series 1100 Megalug product for ductile iron pipe is rated at 350 psi in that size. Given that the cross-sectional area of the 12-in. pipe is 136.9 sq in., the dead end thrust produced at this pressure is an actual 47,915 lb. The 2000PV restraint is rated at 150 psi on DR18 PVC pipe. In this case the dead end thrust is 20,535 lb. Both of these products have been pressure tested to 700 psi.

To demonstrate the performance of the pipe restraints more vividly a Caterpillar D7 bulldozer was employed in an unusual test. This machine weighs over 50,000 lb.

An 1112 Megalug was assembled on each end of a piece of ductile iron pipe, eight feet in length. Threaded rods 12 in. long were used to connect each restraint to a clevis so that the pipe could be suspended by a crane. Wire cable straps were attached to connect the bulldozer to the pipe, and the pipe to the crane, as the photographs show. A gap can be seen between the end of the pipe and the clevis, clearly showing that no other restraints were used in the demonstration assembly. When all was ready the bulldozer was raised and suspended with no difficulty for about 15 minutes.

Ductile iron pipe test	PVC pipe test Click on image for larger view

The procedure was repeated using the 2012PV restraint and DR18 PVC pipe, with the same arrangement of restraints, pipe and clevis. Once again the bulldozer was held successfully in suspension for 15 minutes in each case, providing an impressive demonstration of the holding capacity of these pipe restraint devices.

Edited by Ian Lisk