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High Strength Bolt Tightening and Verification Techniques for Steel Connections: In-Depth Study and National Survey

Yoon-Si Lee, Brent Phares


The current means and methods of verifying that high strength bolts have been properly tightened is 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, there are drawbacks such as being costly, time-consuming, and impractical to use in the field. 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 nationwide survey were conducted to collect and review information on various bolt tightening and verification techniques such that an understanding of available and under-development techniques could be obtained. Also, the requirements for materials, inspection and installation methods outlined in the Research Council on Structural Connections specifications were reviewed and summarized. The technology review effort presented herein was intended to seek a methodology or techniques which, in the near or long term, can be used to quantitatively and accurately determine the stress level in bolted connection. This required a preliminary evaluation of currently available technologies, including numerous nondestructive evaluation techniques that either have been proven in the laboratory or appear to have potential for bolt stress measurement. This paper summarizes all of the work completed during this project.

Keywords: High strength bolt; tightening; verification; pretension.

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