What term refers to the phenomenon when the structure's center of mass does not coincide with its center of rigidity?

The phenomenon where a structure's center of mass does not coincide with its center of rigidity is referred to as torsion or torsional shear stress. This condition can lead to rotation or twisting of the structure under lateral loads, such as wind or seismic forces.

When the center of mass is offset from the center of rigidity, any lateral force applied will create a moment that can cause the structure to twist around its vertical axis. This can lead to additional internal stresses that are not solely due to bending or axial loading. Torsion is particularly significant in the analysis and design of structures as it affects the overall stability and integrity of a building or bridge.

Other options, while relevant to structural analysis, do not specifically describe the relationship between the center of mass and the center of rigidity. Shear stress pertains to forces causing sliding within materials, axial load refers to forces applied along the axis of a member, and bending moment relates to forces that cause bending in beams. None of these terms captures the twisting effect observed when a structure's center of mass is misaligned with its center of rigidity.