Dear Pete,

One final piece of advice, having been in your shoes before....

You have not done as much as possibly could be done. FEA will show your high D/t tees to be a bit more flexible than the simple code formula, also detailed FEA of your exact tank geometry is more reliable than your approximation, therefore qualify your presentation.

After doing so your probably on safe ground stating that despite these shortcomings the magnitude of your loads are such that further refinement won't "make it work".

Therefore your "stress analysis" which is really a stress justification, for a too ridgid layout if it does not meet required loading criteria is not your fault, if the parties involved do not allow for added flexibilty they should be put on notice that this action places them and only them as being responsible for the long term structural integrity of the system as a whole.

The bottom line .... everybody likes to be a back seat driver but if there is an accident its always the drivers fault! If you are the engineer of record then your driving and if your driving you need to use sound engineering judgement and compliance to the pertinent codes in your design. if it breaks and you have not done this an outside expert will be hired to provide testimony that you acted incorrectly, meanwhile all the back seat drivers will have left the scene of the accident!

I hope this help, I love this work but I hate the politics, and the fact that people involved in the desicion process are usually ingnorant.

As a final tool, if another engineer is providing design advice (or restrictions) and if he or she is practicing outside their field of competence (EE, CheE talking about structural integrity for instance) THEY ARE IN CLEAR VIOLATION OF THE NSPE CODE OF ETHICS! Remind them of this as a last resort, but if all else fails this usually does the trick!

Good Luck,

John C. Luf

"Many can cut few are surgeons" T. Paulin