2.23Rigid Diaphragm

In structural analysis of buildings subject to lateral loads, concrete floor slabs are usually considered to be infinitely stiff in their own plane. This assumes that floors displace as rigid bodies and the story shears and torsional moments are distributed to the vertical members (columns and walls) in proportion to their relative stiffnesses.

Modeling of rigid diaphragms in spFrame may be done by attaching infinite in plane stiff beams to the floor diaphragms. These members will share the same in-plane degrees of freedom and will move as a rigid body in the X-Z plane.