The floor joist is an open structural member which is horizontally placed between beams and carries the load of the building for the next set of structural members, which may be vertical. It is these joists that carry the weight of the walls, furniture, appliances, and even people inside a room, as they are part of the floor system, which is what keeps the room at its proper temperature.
In a structure, floor joists play an important role in spreading out the load. The condition of tension is the state in which wood fibers on the bottom of the joist go when weight is applied to the floor and the joist. This causes the top fibers to compress, thereby distributing the load evenly throughout the fibers.