A steel column encased in 3 inches of concrete is rated at how many hours?

The correct answer indicates that a steel column encased in 3 inches of concrete is rated for 4 hours of fire resistance. This rating is significant within the context of fire protection and structural integrity during a fire event. Concrete is known for its excellent thermal properties, which provide substantial insulation to the steel within.

In a fire situation, the concrete serves as a protective barrier, helping to absorb heat and delay the temperature increase of the steel column. The 3 inches of concrete encapsulation adds a significant layer of protection, allowing it to withstand fire exposure for an extended period.

Typically, fire ratings for structural components like steel columns are defined by tests that measure how long they can maintain their structural integrity and load-carrying capacity when exposed to a standard fire. In this case, a 4-hour rating means the encased column can sustain its performance under fire conditions for that duration, which is crucial for ensuring the safety of a building's occupants and the ability for a controlled evacuation during an emergency.

Understanding these ratings helps firefighters and building managers assess structural safety and develop firefighting strategies in emergency situations.