Crack Monitoring Of Composite Beam Bridge Deck Using BOTDA

Composite bridge deck features light weight, easy and quick construction, hence itis a deck system with broad applications in the future. However, durability of this kinddeck system is an unsolved problem. The deck is prone to cracking due to traffic loadand temperature change, which leads to durability problem. Therefore, it is ofimportance to develop technologies for crack monitoring of composite bridge decks.Cracks in bridge decks are hidden, and at unpredictable locations, and they arehard to detect by currently available technologies. In this paper, a distributed sensingtechnology for deck crack monitoring is developed based on Brillouin Optical TimeDomain Analysis (BOTDA). Extensive experimental investigation and real applicationin Ningbo Qingshuipu Bridge prove the viability of this technology. Detailed researchesare summarized as follows:1. Fiber Optical Bragg Grating sensing technology, Optical Time DomainReflectometer(OTDR) and BOTDA are analyzed and compared, and the latter isselected for deck crack monitoring. Sensing property of optical fiber is experimentalstudied, and strain and temperature sensitivity coefficient of the optical fiber areobtained.2. Steel reinforced concrete beam and concrete bridge deck are designed andconstructed respectively, and they are loaded to crack. The capability of BOTDA tomonitoring crack initiation and propagation in the samples is investigated, and theresults are compared with those by resistance strain gauges and fiber optical gratingsensors. The tests show that distributed fiber optical sensor based on BOTDA can locatemultiple cracks simultaneously with high accuracy.3. Three samples are taked by the deck crack monitoring system on NingboQingshuipu Bridge, and the data are analyzed to reveal the condition of the deck. Thehigh stress areas prone to crack are identified..