TM 5-809-12/AFM 88-3, Chap. 15
(2) Mismatched joints. A partial reinforce-
determining the percentage of steel required, the
ment of slab is required where the joint patterns of
thickness of the reinforced floor slab, and the
abutting or adjacent floor slabs do not match, and
maximum allowable length of the slabs. Figure 5-4
when the pavements are not positively separated by
presents a graphic solution for the design of rein-
an expansion or slip-type joint. The floor slab
forced floor slabs. Since the thickness of a
directly opposite the mismatched joint should be
reinforced floor slab is a function of the percentage
reinforced with a minimum of 0.06 percent of steel
of steel reinforcing, the designer may determine the
in directions normal to each other for a distance of
required percentage of steel for a predetermined
3 feet back from the juncture, and for the full width
thickness of floor slab or determine the required
or length of the slab in a direction normal to the
thickness of floor slab for a predetermined
mismatched joint. Mismatched joints normally will
percentage of steel. in either case, it is necessary
occur at intersections of floor slabs or between
first to determine the required thickness of
regular floor slab and fillet areas (fig 5-3).
nonreinforced floor slab by the method outlined
d. Other uses. Reinforced and continuously rein-
previously (para 5-2) for non reinforced floor slabs.
forced floor slabs may be considered for reasons
The exact thickness (to the nearest 1/10 inch) of the
other than those described above provided a report
floor slab, h , is then used to enter the nomogram in
containing a justification of the need for
figure 5-4. A straight line is then drawn from the
reinforcement is prepared and submit for approval
value of h to the value selected for the thickness of
to HQDA (DAEN-ECE-G), Washington, DC
reinforced floor slab, hr ,and extended to the
20314-1 000, or Headquarters, Air Force
required percentage of reinforcing steel, S , or
Engineering and Services Center (DEMP), Tyndall
drawn from the value h to the value selected for the
AFB, Fla. 32403.
percentage of reinforcing steel, and extended to the
thickness, hr . The thickness, hr , will always be
5-6. Reinforced design.
equal to or less than the thickness, h. It should be
noted that the S value indicated in figure 5-4 is the
a. Thickness design on unbonded base or
percentage to be used in the longitudinal direction
subbase. The design procedure for reinforced
only. For nomral designs, the percentage of
concrete floor slabs uses the principle of allowing a
nonreinforcing steel used in the transverse direction
reduction in the required thickness of nonreinforced
will be one-half of that to be used in the longitudinal
concrete floor slab due to the presence of the steel
dirction. Once the hr and S values have been
reinforcing. The design procedure has been
determined, the maximum allowable slab length L is
developed empirically from a limited number of
obtained from the intersection of the straight line
prototype test pavements subjected to accelerated
and the scale of L . Provision also is made in the
traffic testing. Although it is anticipated that some
nomograph for adjusting L on the basis of the yield
cracking will occur in the floor slab under the design
strength fs of the reinforcing steel. Difficulties may
traffic loadings, the steel reinforcing will hold the
be encountered in sealing joints between very long
cracks tightly closed. The reinforcing will prevent
slabs because of large volumetric changes caused by
spalling or faulting at the cracks and provide a
temperature changes.
serviceable floor slab during the anticipated design
life. Essentially, the design method consists of
5-8
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