Rigid Floor Diaphragm which assumes that the floor is very rigid to experience any in-plane and out-of-plane deformation. The rigid diaphragm action of floors assumes that the floor is stiff enough to undergo rigid body movement.
The rigid floor diaphragm assumption may not be appropriate if a relatively narrow building has closely spaced shear walls (i.e. the shear walls are stiffer than the floor diaphragm). In the case of a low rise building, the floor diaphragms may be flexible compared to the shear walls as in light wood framed construction. For long narrow buildings with deep beams the rigid floor diaphragm assumption has to be evaluated carefully. The presence of a slab opening for elevators or stairs can weaken the floor diaphragm action. Wood and metal decks without concrete fills may not be modeled as rigid diaphragms unless the floor system is braced properly. Hence, the use of these options in softwar requires good engineering decision making based upon the actual site conditions.
The rigid floor diaphragm assumption may not be appropriate if a relatively narrow building has closely spaced shear walls (i.e. the shear walls are stiffer than the floor diaphragm). In the case of a low rise building, the floor diaphragms may be flexible compared to the shear walls as in light wood framed construction. For long narrow buildings with deep beams the rigid floor diaphragm assumption has to be evaluated carefully. The presence of a slab opening for elevators or stairs can weaken the floor diaphragm action. Wood and metal decks without concrete fills may not be modeled as rigid diaphragms unless the floor system is braced properly. Hence, the use of these options in softwar requires good engineering decision making based upon the actual site conditions.