{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,16]],"date-time":"2026-07-16T12:31:31Z","timestamp":1784205091662,"version":"3.55.0"},"reference-count":35,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2022,2,5]],"date-time":"2022-02-05T00:00:00Z","timestamp":1644019200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Since artificial intelligence (AI) was introduced into engineering fields, it has made many breakthroughs. Machine learning (ML) algorithms have been very commonly used in structural health monitoring (SHM) systems in the last decade. In this study, a vibration-based early stage of bolt loosening detection and identification technique is proposed using ML algorithms, for a motor fastened with four bolts (M8 \u00d7 1.5) to a stationary support. First, several cases with fastened and loosened bolts were established, and the motor was operated in three different types of working condition (800 rpm, 1000 rpm, and 1200 rpm), in order to obtain enough vibration data. Second, for feature extraction of the dataset, the short-time Fourier transform (STFT) method was performed. Third, different types of classifier of ML were trained, and a new test dataset was applied to evaluate the performance of the classifiers. Finally, the classifier with the greatest accuracy was identified. The test results showed that the capability of the classifier was satisfactory for detecting bolt loosening and identifying which bolt or bolts started to lose their preload in each working condition. The identified classifier will be implemented for online monitoring of the early stage of bolt loosening of a multi-bolt structure in future works.<\/jats:p>","DOI":"10.3390\/s22031210","type":"journal-article","created":{"date-parts":[[2022,2,6]],"date-time":"2022-02-06T20:40:18Z","timestamp":1644180018000},"page":"1210","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":47,"title":["Vibration-Based Loosening Detection of a Multi-Bolt Structure Using Machine Learning Algorithms"],"prefix":"10.3390","volume":"22","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-1248-428X","authenticated-orcid":false,"given":"Oybek","family":"Eraliev","sequence":"first","affiliation":[{"name":"Future Vehicle Engineering Department, Inha University, 100 Inharo, Mitchuholgu, Incheon 22212, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kwang-Hee","family":"Lee","sequence":"additional","affiliation":[{"name":"Mechanical Engineering Department, Inha University, 100 Inharo, Mitchuholgu, Incheon 22212, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chul-Hee","family":"Lee","sequence":"additional","affiliation":[{"name":"Mechanical Engineering Department, Inha University, 100 Inharo, Mitchuholgu, Incheon 22212, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2022,2,5]]},"reference":[{"key":"ref_1","first-page":"2038421","article-title":"Self-Loosening Failure Analysis of Bolt Joints under Vibration considering the Tightening Process","volume":"2017","author":"Chen","year":"2017","journal-title":"Shock Vib."},{"key":"ref_2","first-page":"1","article-title":"Image-based bolt-loosening detection technique of bolt joint in steel bridges","volume":"1","author":"Park","year":"2015","journal-title":"Int. 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