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March/April 2010
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Low-Alloy Steel Reinforcing Bars

ASTM International Subcommittee A01.05 on Steel Reinforcement has made a significant revision to A706/A706M, Specification for Low-Alloy Steel Deformed and Plain Bars for Concrete Reinforcement. A higher yield strength level, namely Grade 80 [550], has been added to the standard. The term “grade” relates to minimum yield strength in units of “kps/in.2 (megapascals),” i.e., “Grade 80 [550]” implies a minimum yield strength of 80 ksi (80,000 psi) or 550 MPa. Subcommittee A01.05 is under the jurisdiction of ASTM International Committee A01 on Steel, Stainless Steel and Related Alloys.

From its original approval in 1974 until recently, the A706/A706M standard covered a single yield strength level, Grade 60 [420]. The standard was developed in response to the engineering community’s requirements for steel reinforcing bars with controlled tensile properties for use in earthquake-resistant structures and restricted chemical composition for weldability.

In recent years, there has been a movement to add a higher strength grade to the standard. Use of higher strength reinforcing bars can reduce congestion of reinforcement thereby enhancing constructibility in earthquake-resistant structures.

A major issue surfaced during the early stages of developing the proposed revision: Can such Grade 80 [550] steel be produced commercially? Four producers of reinforcing bars, with steel mills located in California, Oregon, South Carolina and Washington, volunteered to make trial heats. The trial heats of steel were rolled into several sizes of reinforcing bars. The successful trial heats confirmed that it was feasible to make the higher strength steel and meet the requirements in the proposed revision for controlled tensile properties and restricted chemical composition.

David P. Gustafson, chairman, Subcommittee A01.05, and a consultant, says the requirements in the recently issued A706/A706M-09b are compatible with the provisions for higher strength steel reinforcement in the American Concrete Institute’s Building Code Requirements for Structural Concrete (ACI 318). Gustafson added that A615/A615M, Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement, was also revised recently with the addition of Grade 80 [550].

CONTACT

Technical Information: David P. Gustafson, Winthrop Harbor, Ill.

Phone: 847-731-3585

ASTM Staff: George Luciw

Phone: 610-832-9710