Building Design and Construction Handbook - Merritt - Ventech!

5.102 SECTION FIVE
FIGURE 5.81 Floors of building distribute horizontal
loads to shear walls (diaphragm action).
decking, its characteristics are, to a large degree, dependent on the attachments of
one unit to another and to the supporting members. Such attachments must resist
shearing stresses due to internal translational and rotational actions.
The stiffness of a horizontal diaphragm affects the distribution of the lateral
forces to the bents and shear walls. For the purpose of analysis, diaphragms may
be classified into three groups—rigid, semirigid or semiflexible, and flexible—
although no diaphragm is actually infinitely rigid or infinitely flexible.
A rigid diaphragm is assumed to distribute horizontal forces to the vertical
resisting elements in proportion to the relative rigidities of these elements (Fig.
5.82).
Semirigid or semiflexible diaphragms are diaphragms that deflect significantly
under load, but have sufficient stiffness to distribute a portion of the load to the
vertical elements in proportion to the rigidities of these elements. The action is
analogous to a continuous beam of appreciable stiffness on yielding supports (Fig.
5.83). Diaphragm reactions are dependent on the relative stiffnesses of diaphragm
and vertical resisting elements.
A flexible diaphragm is analogous to a continuous beam or series of simple
beams spanning between nondeflecting supports. Thus, a flexible diaphragm is con-
FIGURE 5.82 Horizontal section through shear walls connected
by a rigid diaphragm. R � relative rigidity and �v � shear-wall
deflection.