PSSC
Mechanical
- Feb 11, 2008
- 63
In regards to Bednar's procedure for sizing stiffeners for external pressure vessels I have a question.
The required I is determined as Is=((Do^2)*Ls*t/12)*(Sc/E), (Sc/E) also is the variable "A".
In the next revision of the formula the "12" is then revised to "14" for [highlight #FCAF3E]"the collapsing strength of the ring is taken as 10% higher than the strength of the ordinary shell".
[/highlight]
By increasing the denominator the "required Is" is lowered.
This makes sense to me.
But in fig 3.9 where it is given that a section of the shell can be used in addition to the stiffener to calculate the "I's", the only change to the above formula is the number in the denominator is reduced to 10.9, this would have the effect of raising the required moment of inertia which is opposite of the stated objective of [highlight #FCAF3E]"To decrease the size of the stiffener the code allows shell sections adjacent to the stiffener to be included into the required moment of inertia".
[/highlight]
Or am I reading this incorrectly and is "I's" used to calculate the "I" of the actual stiffener/shell combination and not used to determine the required "I" like the "Is" formula (Is=((Do^2)*Ls*t/14)*(Sc/E))?
So that "I's" > "Is" = good?
Thanks for the help.
The required I is determined as Is=((Do^2)*Ls*t/12)*(Sc/E), (Sc/E) also is the variable "A".
In the next revision of the formula the "12" is then revised to "14" for [highlight #FCAF3E]"the collapsing strength of the ring is taken as 10% higher than the strength of the ordinary shell".
[/highlight]
By increasing the denominator the "required Is" is lowered.
This makes sense to me.
But in fig 3.9 where it is given that a section of the shell can be used in addition to the stiffener to calculate the "I's", the only change to the above formula is the number in the denominator is reduced to 10.9, this would have the effect of raising the required moment of inertia which is opposite of the stated objective of [highlight #FCAF3E]"To decrease the size of the stiffener the code allows shell sections adjacent to the stiffener to be included into the required moment of inertia".
[/highlight]
Or am I reading this incorrectly and is "I's" used to calculate the "I" of the actual stiffener/shell combination and not used to determine the required "I" like the "Is" formula (Is=((Do^2)*Ls*t/14)*(Sc/E))?
So that "I's" > "Is" = good?
Thanks for the help.
