Julie:

This thread is going by so fast that I overlooked information in one of your posts.

You are probably aware of this but just in case:

The maximum transverse stress in the front and rear walls in a 24" deep x 24" wide x 10' long vessel is not linear with respect to the maximum transverse stress in a 24" deep x 24" wide by 1' long vessel.

ie. the maximum stress in the 10' vessel is not 10 times the stress in the 1' vessel.

I believe (from trying to remember the content of two chapters in a mechanics of materials book 25 years ago) that the maximum stress can be represented by a 2nd order polynomial:

y = ax^2 + bx +c

where

y= maximum stress

x= 10

a <= 1

b >=1

The values of a, b and c will vary depending on the hinge conditions along the sides and bottom of the front and rear walls.

TR