TM 5-809-3/NAVFAC DM-2.9/AFM 88-3, Chap. 3
expansion joints (BEJ*s). The allowance for
e. At control joints in foundation walls and in floors that support
expansion and the criteria to establish joint spacing
masonry walls.
given herein may be adjusted when climatic
(1) A keyway or interlock will be provided
conditions warrant.
across control joints as a means of transferring
a. Brick expansion. The total unrestrained ex-
lateral shear loads perpendicular to the plane of the
pansion of clay brick masonry walls, Wx, may be
wall. Transfer of bending moments or diagonal
estimated from the following formula:
tension across control joint keyways or interlocks
= [,A + ,T()T)(L)
Wx
(eq 4-1)
should not be assumed. Control joints should be
= [0.0003 + 0.000004()T)](L)
weathertight.
Where:
,A = The coefficient for volume change due to
(2) Control joints in concrete masonry unit
walls will be continuous and vertical. Control joint
moisture expansion. It will be assumed equal to
details must provide an uninterrupted weak plane
0.0003 times the wall length.
,T = The thermal coefficient of expansion for clay
for the full height of the wall, including intermedi-
ate bond beams and masonry foundation walls.
or shale brick. It will be assumed equal to 0.000004
However, reinforcing steel in structural bond beams
per unit length per degree Fahrenheit.
)T = The maximum temperature differential
must be continuous through control joints. Control
joints need not extend into reinforced concrete
expected during the life of the structure, degrees
Fahrenheit. )T should not be assumed less than
foundation walls.
(3) Control joints divide walls into panels
100.
which are separate structural elements. Hence,
L = The length of wall between expansion joints,
locations of control joints effect the relative rigidity
inches.
of wall panels and, in turn, the distribution of lateral
b. Vertical expansion joints. Crack control for
(seismic or wind) forces and the resulting unit
horizontal expansion in brick is mainly accom-
stresses. Therefore, adding, eliminating or
plished by the proper placement of continuous
relocating control joints, where the lateral load
vertical BEJ*s. BEJ*s should be placed and spaced
resisting system is sensitive to control joint loca-
to divide a wall into a series of rectangular panels
tion, will not be permitted once the structural
to control cracking. Since the backer rod and
design is complete.
sealant used for sealing vertical BEJ*s are assumed
(4) The control joint location criteria above
to be only 50% compressible, the computed total
applies to all walls exposed to view where control
expansion value, Wx, must be multiplied by two to
of cracking is important. For walls not exposed to
obtain the required joint width. The maximum
view, a control joint spacing of four times the
vertical BEJ spacing for various expansion joint
widths, based on )T = 100EF, along with desired
diaphragm to diaphragm height or 100 feet, which-
ever is less, may be used.
joint locations of vertical BEJ*s are listed in table
c. Joint Reinforcement. Joint reinforcement dis-
4-2. BEJ*s in parapet walls will be at one half the
tributes local temperature and shrinkage stresses
spacing of the supporting walls below. Vertical
and allows a greater control joint spacing to be
BEJ*s do not transfer bending moment or shear and
used. Joint reinforcement spacing as it relates to
must occur at locations where no load transfer is
control joint spacing is provided in table 4-1. It is
required.
recommended that all walls exposed to view, where
control of cracking is important, have joint
reinforcement spaced not more than 16 inches on
center. Joint reinforcement will be terminated at
control joints.
d. Control joint detailing. Control joints are
either flush, raked, or raked and sealed depending
on specific requirements as given in the guide
specifications.
4-3. Brick walls. Cracking in brick masonry
generally results from a combination of expansion
due to moisture absorption by the brick and thermal
expansion of the brick wall. Detailing of brick
masonry must allow for both horizontal and vertical
expansion of the wall or wythe panels. Crack
control in brick walls is accomplished with brick
c.
Horizontal expansion joints. Crack control
4-2
Previous Page
