Why we use +Y restraint sometimes instead of Y? Thanks all for your opinion..

Borzki,

All you have to do is imagine on what the support restricts. Its depend on what type of support. Here, I attach document that may help you in your studies.



Regards,

Machoguy

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"Do not postpone until tomorrow what you can do today"

+Y is the common type of support where pipe is resting on a steel member. Or pipe is restrained from moving downwards(-Y) direction. At the same time pipe is allowed to move in the upward (+Y) direction by some chance. (Y) type restraint can be specified for restraing the pipe movement in both (+Y) and (-Y) directions. If a gap is specified pipe can move only up to the distance allowed by the gap

Dear Borzki

in your question itself answer is there.+Y indicates single directional supoort and y indicates bidirectional support.

Generally in racks we are using single directional support.Commonly in compressor analysis we use bidirectrional support.Because compressor lines subjected to vibration.so we have to control and take care of vibration for that purpose we are using bidirectional support.

Above indicators are only examples to clear your doubts.

Also read the attached topic chain. Y versus +Y comes into play more when we are using Caesar for the contoversial "Hot sus" manipulatons and running Wind cases ot Thermal cases alone (w/o weight) and of course to help CII converge with friction and other non-linearities.

As a wise man has said, "A man needs to know how to use his tool."

http://www.coade.com/ubbthreads/ubbthrea...h=true#Post8306

Thanks all for the reply and the information you've shared..I'm specifically interested in the theory of lift offs..Thanks for directing me to that discussion forum..

Hi Borzki

We check sustain stress & expansion stress separately in piping stress analysis.
For sustain we consider weight , pressure,( force, displacement if any) but no temperature ( W+P1+D1+F1).
For expansion stress we check only thermal effect.
Some time due to high temperature certain pipe shoe/trunnion move up the support structure called Lift off support.
Now in operating condition also there are sustain stress & expansion stress. If in conventional way we check sustain stress Caesar will understand that support at lift off portion is still working in sustain case because in load case setting we do not mention temperature hence no temperature effect included.
To avoid this kind of ( lift off) issue either we have to make another sustain stress checking by removing that support ( since it is not active at operating time) or we have to make special load case to check hot sustain stress ( operating case-temperature effect).

Regards
Habib

Dear habib

Please give an example how this special load case be made.
Even if i do (Operating-expansion), this expansion was calculated using the wrong sustained stress (operating-sustained*)

Thanks all for the enlightenment...What I've done is make two analysis in cases where there are lift off in supports..First, to check the thermal stresses realistically and the cold sustained I've modelled the support that lifts off as +Y..Secondly, to check the Hot Sustained I simply remove the support that lifts off in the analysis..