{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,30]],"date-time":"2026-07-30T14:18:31Z","timestamp":1785421111736,"version":"3.56.0"},"reference-count":25,"publisher":"MDPI AG","issue":"15","license":[{"start":{"date-parts":[[2026,7,27]],"date-time":"2026-07-27T00:00:00Z","timestamp":1785110400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"crossref","award":["U2433209"],"award-info":[{"award-number":["U2433209"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"crossref"}]},{"award":["U2433209"],"award-info":[{"award-number":["U2433209"]}],"id":[{"id":"https:\/\/ror.org\/01h0zpd94","id-type":"ROR","asserted-by":"publisher"}]},{"name":"Hubei Provincial Natural Science Foundation Joint Fund Key Program","award":["2026AFC1158"],"award-info":[{"award-number":["2026AFC1158"]}]},{"name":"Fujian Provincial Science and Technology Major Special Project","award":["2025HZ041002"],"award-info":[{"award-number":["2025HZ041002"]}]},{"name":"Hubei Provincial Department of Science and Technology","award":["No. 2024BAB022"],"award-info":[{"award-number":["No. 2024BAB022"]}]},{"name":"Unveiling and Leading Technology Project","award":["ZLGS-1"],"award-info":[{"award-number":["ZLGS-1"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Traditional crack monitoring methods, relying on discrete point sensors, cannot capture the full spatiotemporal evolution of cracks. To address this limitation, this paper presents a distributed online monitoring approach using ultra-weak Fiber Bragg Grating (UWFBG) array sensing technology. A 16 m full-scale \u03c0-beam was instrumented with a grating array strain sensing system and tested under progressive mid-span loading until failure. The array successfully detected crack initiation at 848.7 kN (0.9P1) and tracked the transformation from L-shaped to U-shaped cracks, yielding a final crack count of 90 with a maximum width of 1.21 mm and length of 246.5 cm at 1791.7 kN. The strain\u2013load curves exhibited a clear linear-to-nonlinear transition and continuous slope increase, closely matching manual observations. Quantitative correlation analysis further established a strong linear relationship between UWFBG peak strains and manually measured crack widths, with the fitting equation \u03b5=7918\u00b7w\u2212110 and a coefficient of determination R2 = 0.971, providing a specimen-specific basis for strain-based crack severity estimation that requires in-situ calibration before field application. The UWFBG array maintained stable signal acquisition throughout the entire loading process, offering superior data continuity and measurement range compared to resistive strain gauges, which suffered progressive data loss after cracking. The results demonstrate that the proposed method can provide real-time, full-field strain mapping and quantitative crack evolution monitoring, offering a powerful tool for bridge health assessment.<\/jats:p>","DOI":"10.3390\/s26154779","type":"journal-article","created":{"date-parts":[[2026,7,27]],"date-time":"2026-07-27T16:11:56Z","timestamp":1785168716000},"page":"4779","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Experimental Research on Online Monitoring of Crack Evolution Process of \u03c0-Type Beams Based on Ultra-Weak FBG Array Sensing Technology"],"prefix":"10.3390","volume":"26","author":[{"ORCID":"https:\/\/orcid.org\/0009-0001-5721-4742","authenticated-orcid":false,"given":"Qiuming","family":"Nan","sequence":"first","affiliation":[{"name":"National Engineering Research Center of Fiber Optic Sensing Technology and Networks, Wuhan University of Technology, Wuhan 430070, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0002-2854-2744","authenticated-orcid":false,"given":"Yichan","family":"Zhang","sequence":"additional","affiliation":[{"name":"School of Mechanical and Electronic Engineering, Wuhan University of Technology, Wuhan 430070, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4012-4839","authenticated-orcid":false,"given":"Juncheng","family":"Zeng","sequence":"additional","affiliation":[{"name":"Fujian Provincial Expressway Technology Innovation Research Institute Co., Ltd., Fuzhou 350001, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9300-5895","authenticated-orcid":false,"given":"Sheng","family":"Li","sequence":"additional","affiliation":[{"name":"National Engineering Research Center of Fiber Optic Sensing Technology and Networks, Wuhan University of Technology, Wuhan 430070, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0579-1257","authenticated-orcid":false,"given":"Lina","family":"Yue","sequence":"additional","affiliation":[{"name":"National Engineering Research Center of Fiber Optic Sensing Technology and Networks, Wuhan University of Technology, Wuhan 430070, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0002-6073-4535","authenticated-orcid":false,"given":"Yan","family":"Yang","sequence":"additional","affiliation":[{"name":"National Engineering Research Center of Fiber Optic Sensing Technology and Networks, Wuhan University of Technology, Wuhan 430070, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0004-1751-2405","authenticated-orcid":false,"given":"Min","family":"Zhou","sequence":"additional","affiliation":[{"name":"Fengli Optoelectronics Technology Co., Ltd., Wuhan 430070, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0000-1449-9955","authenticated-orcid":false,"given":"Qi","family":"Hu","sequence":"additional","affiliation":[{"name":"School of Information Engineering, Wuhan University of Technology, Wuhan 430070, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,7,27]]},"reference":[{"key":"ref_1","first-page":"1306012","article-title":"Overview of Large-Scale Grating Array Fiber Optic Sensing Networks and Applications","volume":"62","author":"Gui","year":"2025","journal-title":"Laser Optoelectron. 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