TM 5-809-12/AFM 88-3, Chap. 15
(b) Reinforced slabs. Transverse contrac-
(5) Doweled and tied contraction joints.
(a) Dowels are required in transverse
tion joints in reinforced concrete slabs should not be
constructed at intervals of less than 25 feet nor more
contraction joints. Dowel requirements and
than 75 feet. Maximum allowable slab width and
specifications are given in paragraph 5-7d.
(b) For nonreinforced slabs, deformed tie
length may be determined from the equation
bars, which are 5/8 inch in diameter, 30 inches long,
and spaced on 30-inch centers, will be required in
3
longitudinal contraction joints that fall 15 feet or 1es
0.00047 hr (fsS)2 # 75
L'
(eq 5-2)
from the free edge of paved areas greater than 100
feet in width to prevent cumulative opening of these
joints.
b. Construction joints. Construction joints are
where
provided to separate areas of concrete placed at
L = the maximum length (or width), feet
different times. They may be required in both the
hr = the reinforced slab thickness, inches
longitudinal and transverse directions. The spacing
fs = the steel yield strength, pounds per square
of construction joints will depend largely on the size
inch
and shape of the floor slab that is being placed and
S = steel reinforcing ration, percentage
the equipment used to place it. Joint spacing will
also be affected by column spacing and bay sizes.
Allowable slab dimensions can be determined
Longitudinal construction joints, generally spaced
directly from figure 5-4 for a yield strength of
20 to 25 feet apart but may reach 50 feet apart
60,000 pounds per square inch. Selection of final
depending on construction equipment capability,
spacing should be based on local conditions. Where
will be provided to separate successively placed
only a portion of the slabs are reinforced, joint
paving lanes. Tranverse construction joints will be
spacing should be a maximum commensurate with
installed when it is necessary to stop concrete
the unreinforced slab configurations.
placement within a paving lane for a sufficient time
(4) Spacing of longitudinal contraction
for the concrete to start to set. All transverse
joints. Contraction joints will be placed along the
construction joints will be located in place of other
centerline of paving lanes that have a width greater
regularly spaced transverse joints (contraction or
than the indicated maximum spacing of transverse
isolation types). There are several types of
contraction joints in table 5-2. These joints may also
construction joints available for use, as shown in
be required in the longitudinal direction for overlays,
figures 5-9, 5-10, and 5-11 and as described below.
regardless of overlay thickness, to match joints
The selection of the type of construction joint will
existing in the base pavement unless a bond-
depend on such factors as the concrete placement
breaking medium is used between the overlay and
procedure (formed or slipformed) and foundation
base slab or the overlay slab is reinforced.
conditions.
5-16
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