If the temperature increases by 30F, how much will an unencased steel frame expand per 100 ft?

• A. 1/16 inch
• B. 3/32 inch
• C. 1/8 inch
• D. 1/4 inch

Answer: (D)

When steel heats up, it expands in a way that is proportional to its length and the temperature increase. The typical linear coefficient of thermal expansion for steel is about 6.5 × 10^-6 per degree Fahrenheit.

For a 100 ft length, convert to inches: 100 ft equals 1,200 inches. A temperature rise of 30°F gives a change in length ΔL = α × L × ΔT = (6.5 × 10^-6) × 1,200 × 30 ≈ 0.234 inches.

So an unencased steel frame would expand by about 0.23 inches, which is essentially a quarter inch per 100 ft for a 30°F rise. This is why allowances are often made in steel framing for thermal expansion, and why the option closest to that value (about 1/4 inch) is the best match.