What is the fire resistance rating of a steel column encased in 3 inches of concrete?

The fire resistance rating of a steel column encased in 3 inches of concrete is typically classified as 1 hour. This rating is based on the ability of the concrete encasement to protect the steel from the high temperatures of a fire, which can cause the steel to lose its structural integrity. The thickness of 3 inches of concrete generally provides sufficient insulation to maintain the column's strength for at least 1 hour under standard conditions prescribed by fire safety codes.

Concrete is a non-combustible material that does not burn and, when applied as an encasement for steel, effectively slows heat transfer to the steel column. Specifically, the temperature of the steel must remain below critical levels to ensure that the column continues to support loads during a fire event. As insulation thickness increases, so does the fire resistance, but the specific rating for 3 inches typically aligns with the 1-hour standard, with greater thicknesses providing correspondingly longer protection.

In this scenario, the rating of 4 hours is much greater than what is typically associated with such a configuration, indicating a misunderstanding of fire resistance ratings for encased columns.