Hello,

I hope everyone is doing fine. I have a question concerning the support loads on the vertical riser clamps. I have an 1800 mm GRP pipe with a vertical run of about 25 m, and is supported at three locations with riser clamps. I have sized the clamps so that each one carries the weight of the piping above it till the next clamp. However, in the restraint load summary I found that the lowest clamp carries all the load, while the above two clamps have zero loads. Is that what would happen actually in operation that all the load would be carried by the lowest clamp? Are there any changes to be made to the model to distribute the loads on the three clamps?

I attached the model for your kind review. The riser clamps are modeled as +y restraints at the nodes 1140, 1145, and 1150. Thanks a lot in advance.

If the pipe is vertical, it grows and contracts such that in the hot condition, the upper supports lift off. In the cold condition the lower supports lift off.

The only way you can distribute the load across the temperatures is if the supports are capable of moving with the pipe. For that, you would need to model the flexibility of the supports, either with structural steel within CAESAR, or by working closely with your structural engineering group.

If the vertical pipe is fairly self-supporting - i.e. it won't fail under its own weight, you can get around this with one massive support, generally at the top.

If it won't support its own weight, you generally have to provide hard supports along the length of the pipe, but then ensure the piping is flexible enough to not exceed code stresses.

I really appreciate your response a lot. The loads are zero for all the load cases, not only the expansion load case, so it is not due to pipe thermal expansion.

You said the pipe can be supported by a single support, generally at the top. What difference it makes if the support is from the top or the bottom?

Your pipe is very stiff axially. That, in combination with your rigid supports along the line will not allow the total load to be shared as you wish.

I might suggest modelling these riser supports as very stiff "hangers" where you provide the hanger pre-load. That would even out the distribution. Once you see how this goes, you can return some of your rigid supports to the model.

From a pipe stress standpoint, little, if none. Tension versus compression. But that's what CAESAR tells you.

One way gravity assists you in keeping your piping configuration. The other way gravity fights you in keeping your piping configuration.

If for whatever reason you lose your guides, you could either be moderately unsafe, or you can be at risk of catastrophic failure.