Cast Iron Load Rating

All castings manufactured by U.S. Foundry are proof load tested in accordance with the destructive testing protocol below, and are assigned one of the following four load rating designations:

• Non-Traffic:  These castings are intended for areas such as sidewalks, terraces, and other areas not subject to vehicular traffic loads.

• Medium Duty:  Castings bearing this designation are able to withstand occasional vehicular loading, but are not intended to receive heavy highway traffic.  Applications include driveways, parking lots, and ramps.

• Heavy Duty:  These castings are manufactured to withstand highway traffic loads, exceeding AASHTO H-20/HS-20 specifications (wheel loads of 16,000 pounds with a tire contact area of 8” x 20”) 25,000 pounds proof load in accordance with CID A-A 60005 or 40,000 pounds proof load per AASHTO M-306.

• Extra Heavy Duty:  For traffic applications requiring even greater load bearing capability, or where increased safety factors are necessary. When castings in this load rating designation are required, please advise loading conditions including total wheel load, tire contact area and tire pressure.  

Designation	Load Application	Minimum Proof Load Test	Reference Specification
Non-Traffic	Sidewalks, terraces	1000 pounds	-
Medium Duty	Parking lots, driveways	18,000 pounds	-
Heavy Duty	H-20 Traffic	25,000 pounds or 40,000 pounds	CID A-A 60005 or AASHTO M-306
Extra Heavy Duty	Concentrated loads	_	_

Proof load test is the recommended method for determining a casting’s load performance. This testing procedure is detailed in Federal Specification CID A-A 60005 and AASHTO M 306. The fundamentals aspects of the test are:

• A specified load is applied over a 9" x 9" contact area at the center of the casting.
• The load is held for a period of 1 minute.
• The cover, grating or frame is inspected for cracks or permanent deformation.
• Any crack or detrimental permanent deformation will cause the castings to be rejected.
• Most tests are performed with loads greater than those specified, even to destruction.

Referenced Specifications

There are several published specifications that are available to assist designers in specifying iron castings.

It is the responsibility of the designer to determine if one or all of these specifications are appropriate for a given application. These specifications are referenced as follows:

• Federal Specification CID A-A 60005 - Frames, covers, gratings, steps, sump and catch basin manhole

• ASTM-A-48 - Standard Specification for Gray Iron Castings

• AASHTO-M 105 - Standard Specification for Gray iron Castings

• AASHTO-M 306 - Standard Specification for Drainage Structure Castings

* ADA – Americans with Disabilities Act.