Calibration Tests of A490 High-Strength Bolts

Tests were conducted on two lots of A490 bolts at Lehigh University and the University of Illinois to determine if testing procedures constitute a variable. Over 100 calibration tests were conducted of 7/8-in. by 5 l/2-in. and 7/8-in. by 9 1/2-in. ASTM A490 high-strength bolts. These included 40 direct tension tests and 60 torqued-tension tests. The torqued-tension tests were conducted in hydraulic calibrating devices and in solid steel blocks. Data on bolt tension, elongation, turns-of-nut, and general behavior were analyzed. The tests showed no significant difference between the results obtained at the two universities. The tests showed that the direct tensile strength was 10% to 20% greater than the torqued tension strength. Only the shorter bolts (7/8-in. by 5 l/2-in.) reached proof load after one-half turn from snug. Comparisons of bolt behavior when torqued in the hydraulic bolt calibrator and in the solid steel block showed that less load was induced into the bolt at one-half turn in the hydraulic calibrator. This study shows that additional rotation beyond one-half turn is necessary for the longer A490 bolt if the proof load is to be reached.