A good rule-of-thumb for a preliminary estimate of panel thickness is to take
the laterally unsupported height in feet (usually floor to roof) and divide
by four. this gives the thickness in inches, and equates to an h/t of 48,
which is commonly used.
A reference covering all phases of tilt-up, inlcuding engineering per '97
UBC, is The Tilt-Up Design & Construction Manual, 5th Edition, authored by
yours truly, and now published by the Tilt-Up Concrete Assn
(www.tilt-up.org). Phone: (319) 895-6911.