Spring support stiffness & Retraint support stiffness

[JJARI]

Hello, everyone. does anybody can give me the difference of Spring support stiffness from Retraint support stiffness? I asked COADE but the answer was "it's same".
However when I got results of input files in CII 5.10 , they were different. thanks a lot.

 

[ApC2Kp]

JJARI,

If it is a fixed support, then I think the CAESARII default stiffness is something like 1E12 lb/inch, or less than infinity but a milliion times more than typical structural stiffnesses in a commercial building. The support loads are then conservative when considering restraints like guides and line stops to limit thermal deflections. If the structural steel flexibility is included, then the piping does move a little more, maybe a few mills.

The stiffness of a spring suport like Grinnell Fig B-268 size 9 would be 200 lb/inch, and from sizes 1 to 22 the stiffnesses could range from 21 lb/in to 8335. lb/in (also termed to be S.R. = spring rate). CaesarII will select the spring size and load for a particular location in the piping model, based on the expected weight load and thermal movement. I have found their spring selection algorithm to be very dependable.

 

[doberdorks]

Also, if you have a restraint instead of a spring the difference may be preload.

SLH

 

[JJARI]

Thank you for your kind answer. ApC2Kp, doberdorks.

However, When I considered Sustain case , they were different results. There is no thermal case, just only weight. It's conservative not concerning with spring's moving. I don't understand in this case. Thank you for replying.

 

[ApC2Kp]

JJARI,

There is a check of the piping movement for spring selection, and when the movement is zero or less than a small fraction, say 1/16 inch, then the spring selection will default back to a rigid support. That might be why you heard that the support stiffness is the same.

There probably is not a need for the spring supports, if no thermal case would exist.