Rigid Moment-Resisting Frame Walls: The Frame Method of Analysis - The Analysis of Irregular Shaped Structures - page 496

2

CM wC

()

M = - -

6

moment at inside face of left pier

face 26 2

2

x = distance from node N oweb splicenearest l 2 eftjoint

The joint locations shown in Fig. 14.8 assume that a full length of sheathing starts at
the outside edge of the wall (8 ft minus C 5 ).

wx

2

MVxM =+-

2

moment at websplicenearest l eftjoint

jnt 2

2

Maximum positive moments for header (see Fig. 14.8):

+ M max is located where V = 0

Moments used to determine tie strap forces, at right end (left end similar):

MMM
strap

= or whicheverisgreater

3 2

Note: The maximum tie strap moment is determined by applying the lateral forces to
the frame acting in both directions. If the axial force from the header is tension, the pro-
portioned bottom flange tension force must also be added to the strap force.
The maximum shear on the header section can be determined by similar triangles
as shown at the bottom of the figure.
All members must be checked for combined bending plus axial forces.

14.3 Composite Glued Sections

Plywood Webs
The section properties and allowable stresses for the plywood can be found in the
Plywood Design Specification (PDS). 9 If oriented strand board (OSB) is used, the Panel
Design Specification 10 should be referenced. Plywood webs are primarily stressed in
shear through their thickness but can also be used to resist bending. The orientation of
the face grain (FG) of the plywood can have a significant effect on the section properties
and therefore must be determined before the section properties can be calculated. When
calculating the moment of inertia of the plywood webs in bending, only the continuous
parallel-grain material in the direction of the stresses is used. This information can
be found in APA's Plywood Design Specification , Tables 1 and 2. The total thickness of
the parallel plies ( t � ) is 1/12 of the appropriate area ( A � ) for tension and compression.
The table shows that the thickness for parallel-grain material when the stress is applied
perpendicular to the face grain is considerably less than when the stress is applied par-
allel to the face grain. This is so because of the layup of the plywood. For an example, a
5-ply layup would have three layers oriented in the direction of the face plies with two
inner perpendicular plies. PDS Sections 2 and 3 provide a complete discussion of the
topic. Figure 14.9 shows two possible layouts, each of which affects the strength and
stiffness of the individual sections. In the ideal condition for the layout of the sheathing,
the entire length of a header or pier section has the face grain oriented parallel to the
neutral axis of the member, as shown in layout 1. It is also ideal when the plywood webs
do not have to be spliced. However, due to the longer spans often encountered, this is