What defines the stiffness and stability of a structure in response to lateral forces?

The center of rigidity is a crucial concept in structural engineering that defines how a structure reacts to lateral forces, such as those caused by wind or earthquakes. It represents the point in a building where the lateral forces are distributed and where the structure has its stiffness concentrated.

When lateral forces act on a structure, it tends to deform or sway. The center of rigidity refers to the point where the building's resistance to this movement is effectively located. A well-designed structure will have its center of mass and center of rigidity aligned as closely as possible. This alignment helps minimize torsional movements and the associated stresses in the structure, thereby enhancing stability.

Structures with a well-placed center of rigidity can resist lateral forces more effectively, making them less likely to experience excessive deflection or damage. This is particularly significant in tall structures or those subjected to variable loads, as the distribution of stiffness influences the overall dynamic behavior of the building.

In contrast, concepts like the center of mass, soft story, and story drift involve different aspects of building design and behavior but do not primarily define how the stiffness and stability of a structure are impacted by lateral forces.