Building Design and Construction Handbook - Merritt - Ventech!

11.14 SECTION ELEVEN
to distribute the load to the masonry within allowable bearing stresses. Length of
bearing should be at least 3 in. Lightly loaded members may be supported directly
on the masonry if the bearing stresses in the masonry are within permissible limits
and if length of bearing is 3 in or more.
Masonry should not be supported on wood construction.
11.3.5 Corbeling
Where a solid masonry wall 12 in or more thick must be increased in thickness
above a specific level, the increase should be achieved gradually by corbeling. In
this method, successive courses are projected from the face of the wall, as indicated
in Fig. 11.3f.
The maximum corbeled horizontal projection beyond the face of a wall should
not exceed one-third the wall thickness for walls supporting structural members. In
any case, projection of any course of masonry should not exceed 1 in.
Chimneys generally may not be corbeled more than 6 in from the face of the
wall. In the second story of two-story dwellings, however, corbeling of chimneys
on the exterior of enclosing walls may equal the wall thickness.
11.3.6 Openings, Chases, and Recesses in Masonry Walls
Masonry above openings should be supported by arches or lintels of metal or reinforced
masonry, which should bear on the wall at each end at least 4 in. Stone
or other nonreinforced masonry lintels should not be used unless supplemented on
the inside of the wall with structural steel lintels, suitable masonry arches, or reinforced-masonry
lintels carrying the masonry backing. Lintels should be stiff
enough to carry the superimposed load with a deflection of less than 1 ⁄720 of the
clear span.
In plain concrete walls, reinforcement arranged symmetrically in the thickness
of the wall should be placed not less than 1 in above and 2 in below openings. It
should extend at least 24 in on each side of the opening or be equivalently developed
with hooks. Minimum reinforcement that should be used is one No.5 bar for
each 6 in of wall thickness.
In structures other than low residences, masonry walls should not have chases
and recesses deeper than one-third the wall thickness, or longer than 4 ft horizontally
or in horizontal projection. There should be at least 8 in of masonry in back
of chases and recesses, and between adjacent chases or recesses and the jambs of
openings.
Chases and recesses should not be cut in walls of hollow masonry units or in
hollow walls but may be built in. They should not be allowed within the required
area of a pier.
The aggregate area of recesses and chases in any wall should not exceed onefourth
of the whole area of the face of the wall in any story.
In dwellings not more than two stories high, vertical chases may be built in 8in
walls if the chases are not more than 4 in deep and occupy less than 4 ft 2 of
wall area. However, recesses below windows may extend from floor to sill and may
be the width of the opening above. Masonry above chases or recesses wider than
12 in should be supported on lintels.