Perhaps http://www.aluminum.org/AM/Template.cfm?Section=20... might help.

Southwire has the rights to the old Alcoa Sag10 program that will calculate sags and tensions for conductors but it is quite expensive. Southwire has a conductor manual available that I believe has all the equations. Aluminum creep is estimated in the programs by using testing of samples for 1000 hours and making an assumption on how it will behave after 40 years.

PLS-Cadd has several Tech-Notes available on their web site, but PLS-CADD has been used by the majority of Utilities and consultants in the USA and probably in the world. Many have tried to verify the sag of wire and have accepted that PLS gives a close enough answer.

The creep data is gathered by test at a constant temperature and constant tension for 1000 hours. This data is used to extrapolate a final creep after many years in the field where the conductor is never at constant tension or temperature. Then you can throw in Elevated Temperature Creep where all aluminum AAC and certain ACSR and ACAR wire will have extra creep when you run it at elevated temperatures (above 90°C).

The bottom line is, we make an educated guess on the sag of wire and then add a couple of feet to be conservative and stay above some Code declared minimum ground clearance.

_____________________________________
I have been called "A storehouse of worthless information" many times.