Q: When rebar have been bent but then aren't used, is it permissible to straighten them in the field for use as straight bars in reinforced concrete?
A: Section 7.3.2 of ACI 318-95, "Building Code Requirements for Structural Concrete," prohibits field bending of reinforcement partially embedded in concrete, except as shown on the design drawings or permitted by the engineer. Though we can't find any reference in ACI 318 to straightening bent bars that aren't embedded in concrete, the commentary for section 7.3.2 cites test results (see reference) showing that ASTM A 615 Grade 40 and Grade 60 reinforcing bars can be cold bent and straightened up to 90 degrees at or near the minimum bend diameter permitted in ACI 318.
In tests, #5, #8, and #11 Grade 60 bars were bent and then straightened at differing temperatures. The researchers concluded that field bending and straightening of reinforcing bars up to #11 should generally be permitted. However, we believe it would be prudent to get the engineer's permission to use straightened bars.
J.P. Stecich, John M. Hansen, and Paul F. Rice, "Bending and Straightening of Grade 60 Reinforcing Bars," Concrete International, American Concrete Institute, Farmington Hills, Mich., August 1984, pp. 14-23.