Design for seismic/ windload - vessel empty of full? 1

[wailunwu]

I would like clarification on the design of vertical vessel skirt, basering and anchor bolts when considering seismic/ wind load. My question is: shall they be designed assuming the vessel is full or empty? Which is the more conservative?

I was told that if designed assuming the vessel is full, the weight would act as moment that counteracts the moment caused by the wind. Thus, designing for empty vessel is the worst case scenario that should be considered.

However, PV Elite shows higher area of anchor bolt and thicker basering are required when the vessel is full compared to when it's empty.

Please explain.

Thank you in advance.

 

[JStephen]

If in doubt, check it both ways.
Usually, controlling case will be wind/empty and seismic/full for anchorage and foundation overturning and wind/full and seismic/full for maximum bearing check.
Often not clearly stated is that contents that are considered in seismic forces are also considered in seismic overturn resistance.
Running all the numbers manually might be enlightening.

 

[TGS4]

As JStephen said, you need to check for the worst case. Sometimes, even a partially-full case may result in the worst.

 

[KevinNZ]

Seismic design is based on probabilities. In our local rules, we do not have look at the worst case liquid level happening at the same time as the design earthquake. We just look at the normal operating level. e.g in process vessel with a controlled level use this level. The chance of the design earth quake hitting when the vessel level is away from normal is much lower than the case the EQ code asks you to design for.

 

[athomas236]

I would still like to be sure that the vessel does not collapse when there is an earthquake, even if higher than code stresses are permitted.

 

[TGS4]

I would still like to be sure that the vessel does not collapse when there is an earthquake...

Are you examining this as a Beyond Design Basis Event (BDBE) or is this something that one could give up to the design margins. And in that spirit, exactly what do you mean by collapse? What additional/reduced margin on collapse would you be looking at?