I don't even know why they have set the spreadsheet up that way, it seems convoluted. Only 3 columns are required (T, delta T and L) imho.
Linear coefficient of thermal expansion for steel α = 0.0000073 in/in °F
Original Length of beam L
0 = 640.69 in
Expanded length of beam L at Temperature T = ???? (what we want to find)
Original (Room) Temperature T
0 = 70 °F
Temperature T = Temperature of beam °F
Change in Temperature ⌂T = T-T
0
L = α*L
0*⌂T
So expansion for a beam at a temperature of 1250°F
=0.0000073 * 640.69 * (1250-70)
=5.5189 inches
The spreadsheet seems to be out a bit. I'm not sure what they are averaging in regard to Average Coefficient and why that's required for the calculation. Does anyone know why?
You can check the calculation here.
http://www.engineeringtoolbox.com/linear-thermal-expansion-d_1379.html