Investigation of Steel Plate Washer Thickness for Column Anchor Rod Applications

Since the 13th edition, the AISC Steel Construction Manual has included provisions regarding the recommended minimum plate washer thickness used in a column base plate and anchor rod assembly. Each plate washer must have sufficient strength and stiffness to fully develop the anchor rod to which it is fastened without succumbing to pull-through, flexural, or cracking failure. Laboratory tensile testing of an anchor rod, nut, and plate washer assembly was conducted at the University of Cincinnati to study plate washer performance. This testing investigated the capacity of ASTM A572/A572M Grade 50 plate washers using the recommended minimum thicknesses as listed in Table 14-2 of the 15th edition of the AISC Steel Construction Manual, with anchor rods having ¾, 1, 1½, 2, and 2½ in. diameter. A total of 94 tests were conducted, after which the plate washers were visually assessed for signs of failure, including measurement of permanent out-of-plane deformation. This assessment established that a 40% relative deformation in plate washers could reasonably be judged as a failure threshold due to excessive deformation. Testing and assessment revealed that while 10 plate washers exhibited relative deformations in excess of 40%, the recommended minimum plate washer thicknesses found in AISC Manual Table 14-2 were sufficient in fully developing most anchor rods. The notable exception to the current minimum thickness recommendations were for washers in use with anchor rods with diameters of ¾, 1, and 1½ in. made from Grade 105 steel. For these anchor rods, a thicker plate washer than that currently specified is recommended. Testing also found that the anchor rod orientation and the variations of ultimate strength in individual anchor rods did not appear to be significantly associated with the performance of plate washers in these tests.