Building Design and Construction Handbook - Merritt - Ventech!

11.16 SECTION ELEVEN
11.4 LATERAL SUPPORT FOR
MASONRY WALLS
For unreinforced solid or grouted masonry bearing walls, the ratio of unsupported
height to nominal thickness, or the ratio of unsupported length to nominal thickness,
should not exceed 20. For hollow walls or walls of hollow masonry units, the ratio
should be 18 or less. For cavity or stone walls, the ratio should not exceed 14. See
‘‘ANSI Standard Building Code Requirements for Masonry,’’ 41.1, American National
Standards Institute.
In calculating the ratio of unsupported length to thickness for cavity walls, you
can take the thickness as the sum of the nominal thickness of the inner and outer
wythes. For walls composed of different kinds or classes of units or mortars, the
ratio should not exceed that allowed for the weakest of the combinations. Veneers
should not be considered part of the wall in computing thickness for strength or
stability.
For nonbearing, unreinforced exterior walls, the thickness ratio should not exceed
20. For unreinforced partitions, the ratio should be 36 or less.
Cantilever walls and masonry walls in locations exposed to high winds should
not be built higher than 10 times their thickness unless adequately braced or designed
in accordance with engineering principles. Backfill should not be placed
against foundation walls until they have been braced to withstand horizontal pressure.
In determining the unsupported length of walls, existing cross walls, piers, or
buttresses may be considered as lateral supports, if these members are well bonded
or anchored to the walls and capable of transmitting forces perpendicular to the
plane of the wall to connected structural members or to the ground.
In determining the unsupported height of walls, the floors and roofs may be
considered as lateral supports, if they can resist a lateral force of at least 200 lb/
lin ft and provision is made to transmit the lateral forces to the ground. Ends of
floor joists or beams bearing on masonry walls should be securely fastened to the
walls (Fig. 11.7). (See also Arts. 11.6 and 11.11.) Interior ends of anchored joists
should be lapped and spiked, or the equivalent, so as to form continuous ties across
the building. When lateral support is to be provided by joists parallel to walls,
anchors should be spaced no more than 6 ft apart and engage at least three joists
which should be bridged solidly at the anchors.
Unsupported height of piers should not exceed 10 times the least dimension.
However, when structural clay tile or hollow concrete units are used for isolated
piers to support beams or girders, unsupported height should not exceed 4 times
the least dimension unless the cellular spaces are filled solidly with concrete or
either Type M or S mortar (Art. 4.16).
Anchors for Masonry Facings. Support perpendicular to its plane may be provided
an exterior masonry wythe, whether it is a veneer (non-load-bearing) or the
outer wythe of a hollow wall, by anchoring it to construction capable of furnishing
the required lateral support. Accordingly, a masonry veneer may be tied with masonry
bonders or metal ties to a backup masonry wall that is given lateral support
or the veneer may be anchored directly to structural framing. Methods of bonding
wythes together are described in Art. 11.3.2. The following applies to anchorage
of masonry walls to structural framing.
Several types of anchors are illustrated in Fig. 11.8. They should be corrosion
resistant. Also, they should be able to resist tension and compression applied by