Tightening Procedures for Proper Installation of Anchor Rods in Ancillary Structures

摘要

In the last 2 decades, many ancillary structures have collapsed, with several instances traceable to loose anchor nuts. According to a quality assurance inspection conducted by the Virginia Department of Transportation (VDOT) in 2012, approximately 30% of the anchor nuts on the inspected ancillary structures across the state of Virginia were found to be loose. The exact cause of the loose anchor nuts is not known; however, one theory is that specified tightening procedures were not properly followed or were not adequate. Currently, a turn-of-the-nut method is used for the tightening of anchor nuts on double-nut moment connections at the base of ancillary structures. This research reviewed current tightening procedures for anchor nuts on ancillary structures. The relationship between three critical tightening parameters-applied torque, nut rotation, and pretension in the rod-was examined. One hundred galvanized steel anchor rods of five different diameters and three different grades were tested. The experimental tests serve as a benchmark to validate the current tightening procedures, as well as to recommend changes.