We have to meet the requirement of Pipe Rack sway ( due to plastic deformation of pipe rack in seismic )in addition to the normal thermal and sustain requirements and inertial seismic and frequency to be 7 Hz,requirements.
Many places we have to remove guides or increase the guide gaps in order to reduce the support loads and equipment nozzle loads.
The frequency calculations, we have done by deleting all gaps in the guides (only for modal analysis), since with gaps the frequency was coming very low.
Is this approach right. To meet all the above requirements we did not find any other solution.

Rakesh,

Support with gaps are a part of "non linear supports" and non linearity is something which CAESAR II dynamic analysis cannot handle.

So what it does is - linearize the non linearity by considering whether the supports are active in that particular case.It does not matter whether you keep 2 mm or 20 mm gap so long the support takes load. The programme cannot differentiate between a large gap and a small gap: it only understands whether the restraint is " active "i.e. load-taking or not.

So please take care when you are specifying which load case you select for linearizing the non linearity.In my opinion if most of the support with gaps are not taking loads in the max. ( or min. ) case , then select the operating temp. case where you may find most of the supports taking load.

This is the only possible approach you can take as non linearity cannot be handled in Dynamic analysis in CAESAR II. I am also not aware of any other commercial pipe stress programme which can handle non linearity in dynamic analysis.

A.Bhattacharya

Stress Analyst

Bechtel Corporation.