I am adding forces and moments to my vessel to represent the loads on the vessel from the piping.

I have operating (no seismic or wind included) forces and moments that I wish to apply to my vessel for base-ring design. However when I add these as forces and moments unless I tick the compute longitudinal stresses BW wind and/or compute longitudinal stresses BS seismic, these forces and moments do not appear to be considered when calculating the governing load case.

How can I consider non-occasional forces and moments?.

Is there a risk that if I have large operating forces and moments I may exceed the allowable operating stresses, however if I consider my operating forces and moments load when calculating the BS or BW stresses, if the seismic loads are low, the occasional load multiplier of 1.2 might result in the occasional loads meeting being satisfied when the operating load case alone is not?

Hello,

When you add global forces/moments to the vessel in PV Elite, you can specify that these forces will act during wind and seismic event. Even if it’s an operating load, it would probably also exist during a strong wind or earthquake. So, typically you will add stresses from your loads to wind/seismic categories (check those boxes to compute BS, BW stresses).

There can be some situation where you do not want to add those stresses to wind or seismic category.

Remember we are not discussing that the loads that you enter are operating or occasional, but how they are combined with other vessel stresses.

When the stresses from your piping loads are combined with occasional stresses from wind/seismic then by default the program increases the allowables by a factor of 1.2. But, you can also choose not to apply this increase factor (Design constraints -> uncheck Use Higher Long. Stress).

I understand your point that there can be a case such that the operating condition stresses are higher and the occasional stresses are within the allowable limit (due to the 1.2 factor). For this situation, go to the Load Cases tab, you will find some blank load cases, add some cases such as

‘FS+BS+IP+OW’ - User force and moment + internal pressure + Operating Weight

And,

‘FS+BS+EP+OW’ - User force and moment + external pressure + Operating Weight

You may also have to consider the load case with no pressure and empty condition (NP+EP).

For the above load cases the 1.2 increase factor will not be used. This will be your additional operating cases.

Next, when you enter the external loads click the box to compute both BS, BW stresses. Then, the program will also combine the stresses due to external loads with wind/seismic and compare it with 1.2 * allowable. This will be the occasional case.

I hope this clarifies it.

Great feedback as always from Coade, thanks Mandeep.