In a recent NextGen update, we removed the automatic vibration-time calculation for vessels not supported from the bottom. The vibration period continues to be calculated automatically on items with skirts, legs, etc. The calculation of the vibration period is part of the larger seismic calculation and therefore intervenes if the latter is enabled.
The removal was necessary because we realized that the method adopted was not actually suitable for half-height supported structures. To complicate the calculation, the fact that a device supported by brackets can be placed on racks or other structures that are subject to oscillations that cannot be estimated by our program.
Our users can therefore end up with -- even on a calculation that did not show messages in previous editions -- a report like this:
Our advice is to rely on the "Pressure Vessel Design Manual" by Dennis R. Moss, chapter "Design of vessel supports", paragraph "Period of vibration", which includes a configuration of this type:
In the notes, the following is stated:
Once the value of the vibration period T has been obtained, it is possible to insert it manually in NextGen, in each affected Load Combination: