Lateral stiffness is a way to define the ability of a frame or beam to resist lateral loads, such as wind loads or seismic loads. Different systems (e.g. moment frames, braced frames, etc.) have different derivations of lateral stiffness.
What is Lateral Stiffness?
Lateral stiffness is not the same as axial or bending stiffness, which apply to individual members. Lateral stiffness defines the ability of a system of members to resist lateral loads. By knowing the lateral stiffness and applying some force, we can calculate the deflection of said frame.
Note that lateral stiffness depends on the applied load pattern. Take the example of the cantilever beam below and consider the stiffness considering two cases: one with a point load; and one with a UDL.
Braced Frame Lateral Stiffness
We can refer to the example of a braced frame to see the derivation of lateral stiffness...