Abstract
Distributed deformation based on fiber Bragg grating sensors or other kinds of strain sensors can be used to monitor bridges during operation. However, most research on distributed deformation monitoring has focused on solid rectangular beams rather than box girders—a kind of typical hollow beam widely employed in actual bridges. The deformation of a single-cell box girder contains bending deflection and also two additional deformations respectively caused by shear lag and shearing action. This paper revises the improved conjugated beam method (ICBM) based on the long-gage fiber Bragg grating (LFBG) sensors to satisfy the requirements for monitoring the two additional deformations in a single-cell box girder. This paper also proposes a suitable LFBG sensor placement in a box girder to overcome the influence of strain fluctuation on the flange caused by the shear lag effect. Results from numerical simulations show that the theoretical monitoring errors of the revised ICBM are typically 0.3–1.5%, and the maximum error is 2.4%. A loading experiment for a single-cell box gilder monitored by LFBG sensors shows that most of the practical monitoring errors are 6–8% and the maximum error is 11%.
Highlights
Monitored deformation is used to evaluate the overall health and safety of in-service bridges and to prevent abnormal states developing
These parts are the bending deflection that is the main portion of the total deformation, AD1 caused by the shear lag effect, and AD2 caused by the shear action
This agreement shows the applicability of the revised improved conjugated beam method (ICBM) for deformation monitoring of a single-cell box girder based on long-gage fiber Bragg grating (LFBG) sensors
Summary
Monitored deformation is used to evaluate the overall health and safety of in-service bridges and to prevent abnormal states developing. Some automatic monitoring techniques, such as the global positioning system [3,4], displacement sensors [5], hydrostatic leveling system [6], and laser measurements [7], have been applied to measure bridge deformation These sensors and systems may be disrupted by environmental factors including bad weather, accidental vibration, or satellite ephemeris error. According to data from a practical deflection monitoring on a multi-span beam bridge, the monitoring error in the second span can rise to over 15% and is significantly higher than the difference of about 3% in the first span [13,14] This error increased because measurement errors accumulate in the double integrating process. Experiments using numerical models and a reduced-scale concrete box girder monitored by LFBG sensors are shown in Section 5 to evaluate the theoretical and actual precision of the revised ICBM
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