Lateral support refers to how the wall is going to perform against applied
horizontal loads (i.e. wind) . This analysis looks at a wall plane as a
simply supported flexural element (beam) spanning between two points of
support. In the traditional sense, the wall is looked at as spanning vertically.
That is, the wall is attatched to the ground, and the roof/floor diaphragm.
When the wind blows the wall wants to deflect like a beam. This bending
stress creates tension on one side of the wall and compression on the other.
As we saw in the compressive stress part
of this guide, masonry is quite fortuitous in compression. Tension, however,
is not handled very efficiently by the masonry wall system. For this reason,
the slenderness ratios which follow are critical to designing a safe, code-compliant
structure. These calculations result in an adequately engineered structure
when and only when all lateral support connections are made. During construction
,when walls are not tied into any structure at the top, walls must be adequately
braced to protect the lives of the tradespersons working on the building
and any passerby.
Masonry walls shall be laterally supported in either the horizontal
or the vertical direction at intervals not exceeding those given below
Construction
Maximum l/t or h/t
Bearing walls
Solid units or fully grouted
All other
20
18
Nonbearing walls
Exterior
Interior
18
36
One can add the nominal thicknesses of multiwythe walls for thickness
Java enabled calculator for hollow bearing walls and exterior
non-load bearing walls (h/t = 18)
Enter wall height in feet and the calculator displays minimum
thickness in inches
Cantilever Walls which are not supported at the top must have a ratio
of height to thickness not exceeding 6
Lateral support can be provided by cross walls, butresses or structural
frame members when the limiting distance is taken horizontally. Or by floors,
roofs acting as diaphragms or structural frambers when the limiting distance
is taken vertically
Mimimum thickness of bearing walls more than one story in height shall
be 8 inches
Bearing walls of one story buildings shal not be less than 6 inches.
Corbelling - the maximum projection beyond the face of the wall shall
not be more than one half the wall thickness or one half the wythe thickness
for hollow walls. The maximum projection of one unit shall neither exceed
one-half the height of the unit nor one-third it's thickness at right angles
to the wall.
