GUIDELINES FOR FACTORY INSPECTION OF PRECAST
MANHOLE COVERS AND FRAMES (As per IS 12529:2002):
1) MarkingP-
Following information shall be clearly and permanently marked on top of each manhole cover and frame:
a) Identification of the source of manufacture;
b) Grade designation denoted by LD-2.5/MD-10/HD-20/EHD-35
c) Any identification mark as required by the purchaser; and
d) Year and month of manufacture of the manhole cover and frame marked at any appropriate location.
Manhole covers and frames shall be of the following four grades and types:
| Grade | Designation | Type/Shape of Cover |
| Light Duty | LD-2.5 | Rectangular, Square, Circular |
| Medium Duty | MD-IO | Rectangular, Square, Circular |
| Heavy Duty | HD-20 | Rectangular (Scrapper Manhole), Square, Circular and Lamp hole |
| Extra Heavy Duty | EHD-35 | ectangular (Scrapper Manhole), Square and Circular |
2) Sampling:-
The number of covers and frames to be selected from the lot shall depend on the size of the lot and shall be according to table given below:
|
No. of Covers or frames in the Lot |
Dimensional Requirements |
No. of samples for Load test on Cover only |
|
|
Sample size |
Acceptance Number |
||
|
Up to 100 |
10 |
1 |
2 |
|
101 to 200 |
15 |
1 |
3 |
|
201 to 300 |
20 |
2 |
4 |
|
301 to 500 |
30 |
3 |
5 |
3) Physical MeasurementsNote :- If the number of covers in the lot is 20 or less, the number of samples for the load test shall be decided by mutual agreement between the purchaser and the manufacturer.
The top and inside surface of frames shall be smooth. To prevent the top outer edge from possible damages, it shall be protected by 25 mm x 3 mm mild steel flat as part of the frame. Sufficient number of steel connectors shall be welded to the inner surface of the mild steel flat so as to connect it with the frame reinforcement and these shall be embedded in the concrete during casting.
Dimensions of Frame
|
Grade Designation |
Description |
Clear Opening in frame, A |
Step Height B |
Sitting ring height C |
Sitting ring width D |
Outer ring width E min |
Top Dia of cover F nominal |
|
LD-2.5 |
Light duty Rectangular |
450 x 600 |
50 |
50 |
50 |
50 |
559 x 708 |
|
LD-2.5 |
Light Duty Square |
400 x400 450 x 450 |
50 50 |
50 50 |
50 50 |
50 50 |
508 x 50 558 x 558 |
|
LD-2.5 |
Light Duty Circular |
370 450 500 560 |
50 50 50 50 |
50 50 50 50 |
50 50 50 50 |
50 50 50 50 |
478 558 608 668 |
|
MD-10 |
Medium Duty Rectangular |
450 x 600 |
70 |
50 |
50 |
50 |
560 x 710 |
|
MD-10 |
Medium Duty Square |
450 x 450 600 x 600 |
70 70 |
50 50 |
50 50 |
50 50 |
560 x 560 710 x 710 |
|
MD-10 |
Medium Duty Circular |
450 500 560 600 |
70 70 70 70 |
50 50 50 50 |
50 50 50 50 |
50 50 50 50 |
560 610 670 710 |
|
HD-20 |
Heavy Duty Rectangular (Scrapper) |
900 x 450 |
90 |
75 |
75 |
75 |
1060x610 |
|
HD-20 |
Heavy Duty Square |
560 x 560 |
90 |
75 |
75 |
75 |
720 x 720 |
|
HD-20 |
Heavy Duty Circular |
450 500 560 600 |
90 90 90 90 |
75 75 75 75 |
75 75 75 75 |
75 75 75 75 |
610 660 720 760 |
|
HD-20 |
Heavy Duty lamp hole |
350 |
90 |
75 |
75 |
75 |
510 |
|
EHD-35 |
Extra Heavy Duty Rectangular |
900 x 560 |
100 |
75 |
75 |
75 |
1060x720 |
|
EHD-35 |
Extra Heavy Duty Square |
560 x 560 |
100 |
75 |
75 |
75 |
720 x 720 |
|
EHD-35 |
Extra Heavy Duty Circular |
450 500 560 600 |
100 100 100 100 |
75 75 75 75 |
75 75 75 75 |
75 75 75 75 |
610 660 720 760 |
NOTES:
1) Tolerance on C shall be ±5 mm, tolerance on ..4, B, D and E shall be +5 ,0 mm.
2) For facility of removing the manhole cover suitable upward taper not more than 5 deg may be provided to Inner periphery of the frame.
3) If required for the removal of the moulds suitable taper not more than 5 deg can be given at the lower inner periphery of the frame.
4) The dimension F for frame is indicative only and has been arrived at based on the nominal values of dimensions A,B and D and a maximum taper of 5 deg on the inner periphery of the frame.
- The maximum clearance at top between the frame and the cover all round the periphery is not more than 5 mm and the top surface of the frame and cover is in level within a tolerance of ± 5mm.
- The minimum diameter of mild steel rod use for lifting device shall be10 for light, 12 mm for medium duty covers and 16 mm for Heavy and Extra heavy duty covers.
- Clear cover to reinforcement shall be not less than 15 mm.
4) Load Test:
Procedure
1) The specified load as given below shall be applied without shock through the medium of a bearing block faced with hard rubber or other resilient material.
2) The bearing block shall be of the size specified in Table given below and shall bear centrally on the cover.
|
Grade of cover |
Type |
Load KN |
Dia of block mm |
|
LD-2.5 |
Rectangular, Square or Circular |
25 |
300 |
|
MD-10 |
Rectangular, Square or Circular |
100 |
300 |
|
HD-20 |
Rectangular, Square or Circular |
200 |
300 |
|
EHD-35 |
Rectangular, Square or Circular |
350 |
300 |
4)All covers shall be submitted to the following tests:3)The block shall be sufficiently rigid to ensure that the load on the cover is uniformly distributed over the full area of the block.
a) Measurement of the permanent set of the cover after the application of 2/3 of the test load.
b) Application of test load.
4.a)Measurement of Permanent Set of the Cover After the Application of 2/3 of the Test Load:
- Before the load is applied take an initial reading at the geometric centre of the cover.
- The load shall be applied at the rate of approximately 0.6±0.4 N/mm/s up to 2/3 of the test load. The load on the test specimen is then released.
- This procedure shall be carried out five times. Then take reading at the geometric centre.
- The permanent set shall then be determined on the difference of the measured readings before the first and the fifth loading.
-The permanent set shall not exceed the following values:
For LD- 2.5 and MD-10 – 1/100time the diameter of the largest circle that can be inscribed in the clear area of the frame
For HD-20 and EHD-35 – 1/300 time the diameter of the largest circle that can be inscribed in the clear area of the frame
4.b)Application of the Test Load
- Immediately after the test according to 4.a, the test load shall be applied at the same rate given in 4.a, the till the full test load is achieved.
- The test load to be maintained for 30±2 s. Cover shall not show cracks in the course of the test.
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