Investigation of the High-Strength Bolt-Tightening Verification Techniques

Research Project


Investigation of the High-Strength Bolt-Tightening Verification Techniques


Principal investigators: Brent Phares, 515-294-5879, (project list), Iowa State University

Project status


Start date: 04/01/14
End date: 03/30/16


Report: March 2016, Investigation of the High-Strength Bolt-Tightening Verification Techniques 1.19 mb (*pdf)

Related publications: Investigation of the High-Strength Bolt-Tightening Verification Techniques 95.64 kb *pdf March 2016

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Sponsor(s): Federal Highway Administration State Planning and Research Funding
Iowa Department of Transportation

About the research


The current means and methods of verifying that high strength bolts have been properly tightened are very laborious and time consuming. In some cases, the techniques require special equipment and, in other cases, the verification itself may be somewhat subjective. While some commercially available verification techniques do exist, these options still have some limitations and might be considered costly options.

The main objectives of this project were to explore high-strength bolt-tightening and verification techniques and to investigate the feasibility of developing and implementing new alternatives. A literature search and a survey of state departments of transportation (DOTs) were conducted to collect information on various bolt-tightening techniques such that an understanding of available and under-development techniques could be obtained. During the literature review, the requirements for materials, inspection, and installation methods outlined in the Research Council on Structural Connections Specification were also reviewed and summarized. To guide the search for finding new alternatives and technology development, a working group meeting was held at the Iowa State University Institute for Transportation October 12, 2015. During the meeting, topics central to the research were discussed with Iowa DOT engineers and other professionals with relevant experiences.

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Phone: 515-294-9501 ~ Fax: 515-294-0467
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