Unit Stresses for Cold-Formed Steel

For sheet and strip of A611, Grade C steel with a specified minimum yield strength Fy  33 ksi, use a basic allowable stress ƒ  20 ksi in tension and bending. For other strengths of steels, ƒ is determined by taking 60% of the specified minimum yield strength Fy. (This procedure implies a safety factor of 1.67.) However, an increase of 331⁄3% in allowable stress is customary for combined wind or earthquake forces with other loads. It should be noted that the 1996 AISI specification uses ‘‘strength’’ (moment, force, etc.) rather than unit stress.