Hi Expert

I want to know about zero weight rigid stiffness in CAESAR (as a construction element). I already seach the forum but i can't find any post describing about zero weight stiffness specifically.
Is it also calculated as a pipe with the same ID and 10*thickness like stated on caesar guide? and if it's calculated as stated on caesar guide, why it'll not deflect in wind load case?
this question is raised when i came up with different method on modeling high rises column which column swaying might occur due to wind exposure.
please kindly advise me on this one and share how to model high rises column.

thank you very much
Bayu

quoting mr Richard on another thread about tank:

Dear Friends,

I had also faced such problems,previous projects, we have practice to model vertical vessel with diameter,thickness,adjust the weight of equipment by fluid density,than model the overhead piping.check nozzle loads, safe the system ,now new client of the current proejct suggest to model rigid with 0 N weight as equipment (vertical vessel) than connect overhead piping.No weight (0 N) Rigid modeling of Equipment.

Overhead piping (in my case) elevation is around to be 26 meter, than after connecting overhead piping with equipment nozzle.

By 2nd case without weight, modeling equipment as rigid,forces & moments are higher.Even Support loads at lugs are also higher.

My knowledge says that wind have affect the weight of equipment at such high elevation. Either we can say 2nd case without weight (0 N) rigid modeling of equipment is very conservative approach. No flexibility of piping & connection with equipment. This is may be over design.

Equipments should be model with proper weight as per equipment dwg shows. Not rigid(0 N)

Please correct me if my points are mismatch with all of you here?

Regards
SND

BayuAdi,

Assume you have a 72 inch diameter vessel, with a 0.1875 inch wall, 40 ft tall. How do you think the deflection of this will compare with a 72 inch diameter vessel, 40 ft tall, with a 1.875 inch wall? (Forget weight, just consider horizontal deflection due to wind.)

SND,

It depends. If you're modeling a pump that is anchored to a slab at grade, then a zero-weight rigid is fine. If you're modeling a vertical vessel, then you want to use a pipe element. I'd use the real weight density, in case this affects system displacments due to boundary condition arrangement.

Mr Richard,

the 0.1875 inch wall will deflect 10times the 1.875 inch wall aproximately.
so when i model high rises column with piping support attached in to it as clip support (either resting or guide) it will be better if I model the column with pipe element to reflect real condition, right? my principal from previous company taught me to model vertical vessel higher than 15m as pipe element, and below 15m is okay to use zero weight rigid element.
my case now is I have to model 5.3m diameter vessel and 33m tall sitting on FPSO topside conected to 30" SS pipe.

Regards,
Bayu

Dear Richard

Thanks,

I will agree with you as I also mentioned the same approach for modeling of vertical vessel, but however due to client's stress incharge recommendation,currently we are modeling rigid piping element only for equipment with 0 N weight.& from Piping nozzle connection as per normal practice.

No argument to justify with them.

Thanks again,my concepts are cleared.

Regards
SND