Load Ratings

Selecting Access Covers and Grates

When selecting an access cover or grate for trafficable areas, consideration should be given to the maximum load the cover will be subjected to in everyday use.  Access covers and grates are given load classifications as set out in Australian Standard 3996 (Access Covers and Grates)

The table below shows load classifications as set out in Australian Standard 3996 (Access Covers and Grates)

 

 

                 

 

 

     
Load Class

A

Extra Light Duty
  Load Class

B

Light
Duty
  Load Class

C

Medium
Duty
  Load Class

D

Heavy
Duty
  Load Class

E

Extra Heavy
Duty
  Load Class

F

Extra Heavy
Duty
  Load Class

G

Extra Heavy
Duty
 
                           
 Traffic Conditions
 Areas (including footways) accessible only to pedestrians and pedal cyclists and closed to other traffic
  Areas (including footways and light tractor paths) accessible to vehicles (excluding commercial vehicles or livestock)
  Malls and areas open to slow moving commercial vehicles
  Carriageways of roads and areas open to commercial vehicles
  General docks and aircraft pavements
  Docks and aircraft pavements subject to high wheel loads
  Docks and aircraft pavements subject to very high wheel loads
 
                           
 Serviceability Design Load (kN)
 6.7   53
  100
  140
  267
  400
  600
 
 Ultimate Limit Design Load (kN) 
 10   80
  150
  210
  400
  600
  900
 
 Nominal Wheel Loading (kg) 

Selecting an appropriate cover or grate also depends on the where it will be installed and the various types of traffic that it may receive. Whilst load classifications provide a guide nominal loads are based on stationary loads, which poorly simulate real world traffic conditions

Also consider:

Dynamic Loads
  Small or Solid Wheels
  Large or Pneumatic Wheels
  Areas at the Base of a Steep Decline
Areas subject to moving traffic will exert a dynamic load which will try to twist a cover out of position.  If traffic moves quickly or turns on a cover, a higher load class should be selected and extra design features should be sought such as slotted drainage, locking grates down with bolts or steel reinforcement
  Small or solid wheels concentrate a heavy load to a very small point where it is transferred to the cover.  This can be the case with forklifts and rubbish skips which often feature solid wheels and cause massive damage to underspecified covers.  A grate or cover with a higher load class will be required in these situations
  Large or pneumatic wheels will spread a load over a larger area and exert a lower stress on the grate or cover.  This is why a heavy tractor can be classified in load class B with smaller vehicles
  Covers at the base of a decline will experience short periods of increased load as a large portion of the vehicles total weight can be transferred to the front wheels.  The cover will be under high stress and a higher load class will required in these situations.

  

Notes:

1. Nominal wheel loads are given for guidance only. Consideration should be given to the type, size and pneumatic pressure of the load applied
2. Class B design loads exceed AS 5100.2 requirements for footway loading
3. Class D design loads exceed AS 5100.2 requirements for a W80 wheel load
4. Class C units are based on an intermediate load