A Novel Comparative Study of European, Chinese and American Codes on Bolt Tightening Sequence Using Smart Bolts

Abstract

Achieving uniform bolt preload distribution is crucial but not easy for a multi-bolt connection. Tightening sequence is one of the primary factors that affect the bolt preload distribution. Different national codes specify details of tightening sequence of a multi-bolt connection. However, few studies have been conducted on the effect of tightening sequence specified by different national codes on bolt preload distributions. In this paper, a novel comparative study of different national codes on bolt tightening sequence was carried out. In order to monitor the variations of bolt preload, smart bolts integrated with fiber Bragg grating (FBG) sensors were designed, fabricated, and calibrated. The FBG-enabled smart bolt can accurately measure the pre-load of each bolt in real time. Then, bolts tightening sequence experiment was performed on a connection of two rectangular steel plates fastened by sixteen smart bolts to compare the bolt preload distributions of different tightening sequences, which are based on European, Chinese and American codes. The experimental results demonstrate that small differences in three tightening sequences can be found and using Chinese code obtains better preload uniformity in a multi-bolt connection by comparison.