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13.7.1 Flat slab tops shall be subject to rejection for failure

to conform to any of the specification requirements. In

addition, an individual flat slab top shall be subject to rejection

because of any of the following:

13.7.1.1 Fractures or cracks passing through the wall, ex-

cept for a single end crack that does not exceed the depth of the

joint.

13.7.1.2 Defects that indicate mixing and molding not in

compliance with

7.1

or surface defects indicating honey-

combed or open texture that would adversely affect the

function of the flat slab top.

13.7.1.3 The planes of the ends are not perpendicular to the

longitudinal axis of the flat slab top, within the limits of

permissible variations prescribed in

13.6

13.7.1.4 Damaged or cracked ends, where such damage

would prevent making a satisfactory joint.

13.7.1.5 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 slab.

14. Risers and Conical Tops

14.1

Scope—

This section covers precast reinforced concrete

risers and conical tops used in construction of manholes for use

in sewer, drainage, and water works.

14.2

Acceptance—

Acceptability of risers and conical tops

covered by this specification shall be determined by the results

of such tests of materials as are required by Section

; by

compressive strength tests on concrete cores or concrete

cylinders required by Section

; and by inspection of the

finished product, including amount and placement of reinforce-

ment as prescribed by either

14.4

14.5

and meeting

permissible variations as prescribed by

14.7

, to determine its

conformance with the design prescribed under this specifica-

tion and its freedom from defects.

14.3

Design—

The minimum wall thickness shall be one

twelfth of the largest internal diameter of the riser or conical

top.

14.4

Welded Steel Cage Reinforcement:

14.4.1

Circumferential Reinforcement for Risers and Coni-

cal Tops:

14.4.1.1 Circumferential reinforcement may consist of ei-

ther one or two lines of steel. The total area of reinforcement

per vertical metre shall be not less than 0.21 times the internal

diameter in millimetres.

14.4.1.2 A line of circumferential reinforcement for any

given total area may be composed of two layers if the layers are

not separated by more than the thickness of one cross member

plus 6 mm. The two layers shall be tied together to form a

single cage. All other specification requirements such as laps,

welds, and tolerances of placement in the wall of the riser or

conical top shall apply to this method of fabricating a line of

reinforcement.

14.4.1.3 Where one line of circumferential reinforcement is

used, it shall be placed in the center third of the wall. The

protective cover over the circumferential reinforcement in the

wall shall be no less than 19 mm in accordance with

14.7

14.4.1.4 Where two lines of circumferential reinforcement

are used, each line shall be so placed that the protective

covering over the circumferential reinforcement in the wall

shall be 25 mm.

14.4.1.5 The location of the reinforcement shall be subject

to the permissible variations in dimensions prescribed in

14.7

14.4.1.6 The spacing center to center of circumferential

reinforcement in a cage shall not exceed 150 mm.

14.4.2

Longitudinal Members—

Each line of circumferential

reinforcement shall be assembled into a cage that shall contain

sufficient longitudinal bars or members to maintain the rein-

forcement in shape and position within the form to comply

with permissible variations in

14.7

14.4.3

Joint Reinforcement—

The tongue or groove of the

joint is not required to contain circumferential reinforcement.

14.5

Steel Hoop Reinforcement:

14.5.1

Continuous Steel Hoop Reinforcement for Risers and

Conical Tops up to and Including 1200 mm Diameter:

OTE

3—Care shall be taken to ensure that none of the steel hoop

reinforcement is cut prior to installation of the riser or conical top.

14.5.1.1 Circumferential reinforcement for manhole risers

and conical tops up to and including 600 mm in height shall

consist of no less than two hoops of steel wire or reinforcing

bars. The steel hoop shall have a minimum cross-sectional

diameter of 6 mm and shall be located in each end quarter of

the riser or conical top, with a minimum distance of 25 mm

from the shoulder of the riser or conical top.

14.5.1.2 Circumferential reinforcement for manhole risers

and conical tops greater in height than 600 mm and up to and

including 1200 mm in height shall consist of no less than three

hoops of steel wire or reinforcing bars. The steel hoops shall

have a minimum cross-sectional diameter of 6 mm, and shall

have a hoop located in each end quarter of the riser or conical

top with a minimum distance of 25 mm from the shoulder of

the riser or conical top. The third, or middle, hoop shall be

located from the shoulder of the riser or conical top a distance

equal to one-half the section height

150 mm.

14.5.1.3 Circumferential reinforcement for manhole risers

and conical tops greater in height than 1200 mm. and up to and

including 1800 mm in height shall consist of no less than four

hoops of steel wire or reinforcing bars spaced equally

mm. throughout the height of the riser or conical top. The steel

hoops shall have a minimum cross-sectional diameter of 6 mm

and shall have a hoop located in each end quarter of the riser

or conical top with a minimum distance of 25 mm from the

shoulder of the riser or conical top.

14.5.1.4 The hoop reinforcement shall be placed in the

center third of the riser wall or conical top. The concrete cover

over the hoop reinforcement in the wall of the section shall be

no less than 19 mm in accordance with

14.7

14.5.1.5 For riser sections with openings, this section

14.5

not permitted.

14.5.2

Joint Reinforcement—

The tongue or groove of the

joint need not contain circumferential reinforcement.

14.6

Joints—

Precast reinforced concrete risers and conical

tops shall be designed and manufactured with male and female

ends, so that the assembled manhole base, riser and conical top

C478M − 15

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