What does the bottom chord in a truss primarily function as?

The bottom chord in a truss primarily functions as a ceiling joist. It plays a crucial role in providing structural support to the ceiling by maintaining the level of the ceiling surface and transferring loads from the ceiling down to the vertical supports or walls.

In many truss designs, the bottom chord also helps to resist tensile forces, allowing it to effectively stabilize the overall truss structure. By serving as a ceiling joist, it connects directly with the ceiling system, helping to distribute weight and allowing for a flat or directly finished ceiling.

While options like rafter, roof beam, and support column have their specific purposes within roofing structures, they do not describe the primary role of the bottom chord as accurately as ceiling joist does. Rafters are inclined members that support the roof covering, roof beams support rafters and distribute loads, and support columns bear vertical loads from the roof and truss system, none of which reflect the specific function of the bottom chord in relation to the ceiling.