{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,13]],"date-time":"2026-04-13T15:16:17Z","timestamp":1776093377648,"version":"3.50.1"},"reference-count":41,"publisher":"MDPI AG","issue":"18","license":[{"start":{"date-parts":[[2022,9,9]],"date-time":"2022-09-09T00:00:00Z","timestamp":1662681600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"National Natural Science Foundation of China","award":["51708164"],"award-info":[{"award-number":["51708164"]}]},{"name":"National Natural Science Foundation of China","award":["KQTD20180412181337494"],"award-info":[{"award-number":["KQTD20180412181337494"]}]},{"name":"National Natural Science Foundation of China","award":["ZDSYS20201020162400001"],"award-info":[{"award-number":["ZDSYS20201020162400001"]}]},{"name":"National Natural Science Foundation of China","award":["GJHZ20200731095802007"],"award-info":[{"award-number":["GJHZ20200731095802007"]}]},{"name":"Shenzhen Science and Technology Program","award":["51708164"],"award-info":[{"award-number":["51708164"]}]},{"name":"Shenzhen Science and Technology Program","award":["KQTD20180412181337494"],"award-info":[{"award-number":["KQTD20180412181337494"]}]},{"name":"Shenzhen Science and Technology Program","award":["ZDSYS20201020162400001"],"award-info":[{"award-number":["ZDSYS20201020162400001"]}]},{"name":"Shenzhen Science and Technology Program","award":["GJHZ20200731095802007"],"award-info":[{"award-number":["GJHZ20200731095802007"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>A high-strength bolt connection is the key component of large-scale steel structures. Bolt loosening and preload loss during operation can reduce the load-carrying capacity, safety, and durability of the structures. In order to detect loosening damage in multi-bolt connections of large-scale civil engineering structures, we proposed a multi-bolt loosening identification method based on time-frequency diagrams and a convolutional neural network (CNN) using vi-bro-acoustic modulation (VAM) signals. Continuous wavelet transform was employed to obtain the time-frequency diagrams of VAM signals as the features. Afterward, the CNN model was trained to identify the multi-bolt loosening conditions from the raw time-frequency diagrams intelligently. It helps to get rid of the dependence on traditional manual selection of simplex and ineffective damage index and to eliminate the influence of operational noise of structures on the identification accuracy. A laboratory test was carried out on bolted connection specimens with four high-strength bolts of different degrees of loosening. The effects of different excitations, CNN models, and dataset sizes were investigated. We found that the ResNet-50 CNN model taking time-frequency diagrams of the hammer excited VAM signals, as the input had better performance in identifying the loosened bolts with various degrees of loosening at different positions. The results indicate that the proposed multi-bolt loosening identification method based on VAM and ResNet-50 CNN can identify bolt loosening with a reasonable accuracy, computational efficiency, and robustness.<\/jats:p>","DOI":"10.3390\/s22186825","type":"journal-article","created":{"date-parts":[[2022,9,9]],"date-time":"2022-09-09T04:54:41Z","timestamp":1662699281000},"page":"6825","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":36,"title":["Loosening Identification of Multi-Bolt Connections Based on Wavelet Transform and ResNet-50 Convolutional Neural Network"],"prefix":"10.3390","volume":"22","author":[{"given":"Xiao-Xue","family":"Li","sequence":"first","affiliation":[{"name":"Department of Civil Engineering, Hefei University of Technology, Hefei 230009, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Dan","family":"Li","sequence":"additional","affiliation":[{"name":"School of Civil Engineering, Southeast University, Nanjing 211189, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Wei-Xin","family":"Ren","sequence":"additional","affiliation":[{"name":"College of Civil and Transportation Engineering, Shenzhen University, Shenzhen 518061, China"},{"name":"Key Laboratory for Resilient Infrastructures of Coastal Cities, Ministry of Education, Shenzhen University, Shenzhen 518061, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jun-Shu","family":"Zhang","sequence":"additional","affiliation":[{"name":"Department of Civil Engineering, Hefei University of Technology, Hefei 230009, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2022,9,9]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"2153","DOI":"10.1590\/1679-78254231","article-title":"A review paper on looseness detection methods in bolted structures","volume":"14","author":"Nikravesh","year":"2017","journal-title":"Lat. 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