What is the term for the lateral displacement of one level relative to the level above or below it?

The term for the lateral displacement of one level relative to the level above or below it is "Story Drift." This concept is particularly important in understanding how structures behave under lateral loads, such as earthquakes or strong winds. Story drift is crucial for evaluating design parameters, ensuring that buildings can withstand forces without excessive movement that could lead to structural damage or failure.

In the context of building design, story drift plays a key role in maintaining the integrity of a structure. Each story may move differently during lateral loading due to variations in stiffness, weight, and the overall dynamics of the building. A high level of story drift could indicate potential issues with the structural support and may necessitate design adjustments to ensure safety and stability.

The other terms listed, while relevant to structural engineering, do not describe this specific lateral displacement phenomenon. A "Soft Story" refers to a level within a building that has significantly less stiffness than the stories above, which can contribute to a higher story drift if not appropriately designed. The "Center of Rigidity" is a point that represents the distribution of lateral stiffness in a building, while "Relaxation" typically refers to a decrease in stress over time in materials under constant strain, which differs from the concept of lateral displacement between floors.