More than 2 saddle supports, Zick?

[MRS957]

Does anyone know of a modification to the Zick analysis that would enable 3 saddle supports instead of 2. Are there any other design methods for using 3 supports. I know that 3 supports are usually not desirable but I am tryinig to determine stresses in an existing unit having 3 saddles.
Thanks in advance!

 

[LSThill]

Hi MRS957 (Mechanical)

Send me at e-mail

Leonard@thill.biz

http://www.thill.biz

 

[athomas236]

always thought more than 2 saddles is statically indeterminant and therefore not an acceptable engineering solution.

athomas236

 

[gramya]

Interesting problem. It has been raised number of times and the same answer that shell become an indterminate structure once supported on more than 2 saddles. But cant we analyse the cylindrical structure supported on multiple supports? The calculation for stresses at mid section of the shell supported between any two saddles shall remain same. If the saddles are equally spaced, then analyse the overhanging shell consiuderation additionally for one of the extreme saddle and then assume that all the intermediates will surely be safe ( over designed). If one want to optimise from such approximate analysis using only Zick formula, try to analyse using FEA/ experimental stress analysis and develop improved equations for stresses giving some imperical factors for more than two saddle cases. Ihope people are using similar approach for even mounded large length ( more than 90 meters length and with 5-6 m diameter shell) storage vessels now used for LPG storages.


Narendra K. Roy
Gramya Research Analysis Institute,
PO box 4016, Vadodara 390015, India
Website:

http://www.gramya.com

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http://www.charismaglobal.com

 

[juancito]

Regarding how can Zick method be used for more than 2 saddles, have a look @ the book od Brownell & Young (if I recall well " Process Equipment Design". I don´t have it at hand, but I used it many years ago for a 5 saddles water accumulator calculation.
Be aware, that for the calculation of saddles reaction, you need to consider not only the vessel stiffness but the kind of support "beneath" the saddles (steel structure??) because the problem can be a continuous beam on elastic supports.

 

[Raydel]

Yes, there is a published method. The European EN13445 pressure vesseal code addrsses this problem. In fact it considers a a larger number of saddles also.