In shear wall or box buildings, which elements act like giant beams under stress?

In shear wall or box buildings, the floor and roof planes can indeed act like giant beams under stress. This is due to their structural role in distributing loads throughout the building. When lateral forces, such as wind or seismic activity, are applied to these structures, the floors and roofs help resist sideways movement by transferring loads to the shear walls.

These planes are typically stiff and capable of carrying loads effectively across their spans, similar to how a beam would. Their structural integrity is critical, as they provide rigidity and stability, preventing excessive sway and maintaining the structure's overall safety. By allowing the floors and roofs to act in this manner, they contribute significantly to the building's resistance to shear forces, enhancing the overall performance during stress conditions.

In contrast, columns primarily serve as vertical support elements, whereas ducts are not load-bearing components. Walls can provide support but do not function like beams in the same way that floor and roof planes do.