ShwaZmoto
Mechanical
- Jul 28, 2008
- 10
First, I must say that this is not a criticism of Compress, but just an observation. Compress does a fantastic job, and is an excellent piece of software.
I did, however, notice something peculiar about Compress and the way it calculates the seismic design force, Fp, using equation 13.3-1 from ASCE 7-05. In regards to the variable Wp, or the component operating weight, Compress uses the vessel's new operating weight, which is correct so as long as all of the external vertical forces placed on a vessel are weights; e.g, forces due to a mass and acceleration. However, if the forces acting on the vessel are massless, such as thermal nozzle loads, and are not due to the acceleration of gravity acting on a mass, then they should not be considered as contributing to the variable Wp since Wp is meant to represent the weight of a mass distribution.
Again, Compress is not doing anything wrong. The software specifies that what you are placing on the vessel is a load, which intrinsically means it is a weight, although this is not spelled out anywhere. I believe many users commonly, and incorrectly, place external loads on vessels to represent massless forces such as thermal loads. This practice is incorrect, is it not?
I did, however, notice something peculiar about Compress and the way it calculates the seismic design force, Fp, using equation 13.3-1 from ASCE 7-05. In regards to the variable Wp, or the component operating weight, Compress uses the vessel's new operating weight, which is correct so as long as all of the external vertical forces placed on a vessel are weights; e.g, forces due to a mass and acceleration. However, if the forces acting on the vessel are massless, such as thermal nozzle loads, and are not due to the acceleration of gravity acting on a mass, then they should not be considered as contributing to the variable Wp since Wp is meant to represent the weight of a mass distribution.
Again, Compress is not doing anything wrong. The software specifies that what you are placing on the vessel is a load, which intrinsically means it is a weight, although this is not spelled out anywhere. I believe many users commonly, and incorrectly, place external loads on vessels to represent massless forces such as thermal loads. This practice is incorrect, is it not?