142 / 237
12.6.1.3 The planes of the ends are not perpendicular to the
longitudinal axis of the grade ring, within the limits of
permissible variations prescribed in
12.5
.
12.6.1.4 Damaged or cracked ends, where such damage
would prevent making a satisfactory joint.
12.6.1.5 Any continuous crack having a surface width of 0.3
mm, or more and extending for a length of 300 mm or more,
regardless of position in the wall.
13. Flat Slab Tops
13.1
Scope—
This section covers precast reinforced concrete
flat slab tops used in the construction of manholes for use in
sewer, drainage, and water works.
13.2
Acceptance:
13.2.1 Acceptability of flat slab tops shall be determined by
the results of such tests of materials as are required by Section
4
; by compressive strength tests on concrete cores or concrete
cylinders required by Section
8
; and by inspection of the
finished product, including amount and placement of reinforce-
ment as prescribed by
13.4
and
13.6
, to determine its confor-
mance with the design prescribed under this specification and
its freedom from defects.
13.2.2 Unless otherwise designated by the owner at the time
of, or before, placing an order, two separate and alternative
methods of acceptance are permitted for flat slab top manufac-
turer designs, in addition to tests of materials and inspection
required in
13.2.1
.
13.2.2.1
Acceptance on the Basis of Proof-of-Design Test—
Acceptance of flat slab tops on the basis of the results of a
proof-of-design test performed in accordance with
13.5
in lieu
of submission of design calculations and detailed drawings.
13.2.2.2
Acceptance on the Basis of Rational Design—
Acceptance of flat slab tops on the basis of design calculations
by a rational method and detailed drawings.
13.3
Design:
13.3.1 The basis of flat slab top designs shall be the
appropriate sections of the latest edition of ACI 318.
13.3.2 Flat slab tops shall have a minimum thickness of 150
mm for risers up to and including 1200 mm in diameter and
200 mm for larger diameters.
13.3.3 The flat slab top access opening shall be a minimum
of 600 mm in diameter.
13.3.4
Joint—
The reinforced concrete flat slab top shall be
formed with or without a male or female end so that when the
manhole base, riser and top section are assembled, they will
make a continuous and uniform manhole compatible with the
tolerances given in Section
13.6
.
13.3.4.1 Joints are designed to perform in axial compres-
sion; therefore, shear or load testing of the joint is not required.
13.4
Reinforcement:
13.4.1 Flat slab tops manufactured with a joint or with other
indication of the top or bottom of the slab shall be manufac-
tured with one layer of reinforcement placed near the bottom
surface so that the protective cover over the reinforcement shall
be 25 mm.
13.4.2 Flat slab tops manufactured without a joint or with-
out other indication of the top or bottom of the slab shall be
manufactured with two layers of steel reinforcement, one
located near the bottom surface and one near the top surface so
that the protective cover over each layer is 25 mm.
13.4.3 A layer of reinforcement shall have a minimum area
of 250 mm
2
/linear m in both directions.
13.4.4 Openings in flat slab tops shall be additionally
reinforced with a minimum of the equivalent of 130 mm
2
of
steel at 90°. Straight rods used to reinforce openings shall have
a minimum length equal to the diameter of the opening plus 50
mm.
13.5
Physical Requirements—
Physical requirements for
tests shall conform to the requirements of Section
8
.
13.5.1
Proof-of-Design Test:
13.5.1.1 If
13.2.2.2
has been designated as the basis of
acceptance, one flat slab top for each design shall be tested
unless the owner has indicated otherwise.
13.5.1.2 The flat slab top proof-of-design test procedures
shall be in accordance with Test Methods
C497
.
13.5.1.3 The ultimate test load shall be the sum of at least
130 % of the dead load on the slab plus at least 217 % of the
live-plus impact load on the slab. Dead load is the mass of the
column of earth over the slab plus the mass of the riser
supported by the slab. Live load is the maximum anticipated
wheel load that may be transmitted through the riser to the slab.
13.5.1.4 The flat slab top shall be acceptable if it supports
the required ultimate test load without failure. Ultimate
strength failure is defined as the inability of the slab to resist an
increase in the applied load.
13.5.1.5 When agreed upon by the owner and manufacturer,
the flat slab top shall be acceptable based on certified copies of
the results of tests performed on identical flat slab tops instead
of requiring new proof-of-design acceptance tests.
13.6
Permissible Variations:
13.6.1
Internal Diameter—
The internal diameter of the flat
slab tops entrance hole shall not vary more than
6
1 %.
13.6.2
Thickness—
The thickness of flat slab tops shall be
not less than that prescribed in the design by more than 5 % or
6
5 mm, whichever is greater. A thickness greater than that
prescribed in the design shall not be cause for rejection.
13.6.3
Length of Two Opposite Sides—
Variations in lengths
of two opposite sides of flat slab tops shall be not more than 6
mm.
13.6.4
Length—
The underrun in length of a flat slab top
shall be not more than 20 mm/m of length.
13.6.5
Position of Reinforcement—
For flat slab tops with
less than a 150-mm thickness, the maximum variation in the
position of reinforcement from that prescribed in
13.5
shall be
6
10 % of the thickness or
6
6 mm, whichever is greater. For
flat slab tops with a thickness greater than 150-mm, the
maximum variation shall be
6
10 % of the thickness or
6
16
mm, whichever is the lesser. In no case, however, shall the
cover over the reinforcement be less than 19 mm.
13.6.6
Area of Reinforcement—
Steel reinforcement areas
that are 10 mm
2
/linear m less than called for by design shall be
considered as meeting the required steel reinforcement area.
13.7
Rejection:
C478M − 15
5
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