About the research
MnDOT is experiencing problems with loose nuts at the anchor bolts of various transportation structures including signs and luminaires. To address this issue, MnDOT funded a research project, which ended in June 2018. In this project, Iowa State University researchers developed specifications (including tables and charts) for tightening and re-tightening of anchor bolts. MnDOT will begin to implement these specifications in a project set to occur from October 2018 to December 2019.
With the to-be-obtained field performance data, this Phase II project will refine the specifications, along with completing other needed research to complete the specifications with regard to snug tight conditions, alternative bolt materials and sizes, grip lengths, continuing fatigue tests, collecting monitoring data, etc. All results will help to complete bolt tightening and re-tightening procedures and specifications that will eliminate or minimize problems associated with loose anchor bolt nuts in MnDOT structures, which will save construction and maintenance costs while simultaneously improving the safety of the traveling public.
The findings from this project will be proposed to the AASHTO T-12 Committee to change the bolt tightening procedures.