Distributed Deformation Monitoring for a Single-Cell Box Girder Based on Distributed Long-Gage Fiber Bragg Grating Sensors

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%.

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Distributed Deformation Monitoring for a Single-Cell Box Girder Based on Distributed Long-Gage Fiber Bragg Grating (LFBG) Sensors

10.20944/preprints201806.0166.v1 ◽

2018 ◽

Author(s):

Sheng Shen ◽

Shao-fei Jiang

Keyword(s):

Single Cell ◽

Fiber Bragg Grating ◽

Maximum Error ◽

Deformation Monitoring ◽

Strain Sensors ◽

Bragg Grating ◽

Shear Lag ◽

Box Girder ◽

Hollow Beam ◽

Lag Effect

Distributed deformation based on Fiber Bragg Grating sensors or other kinds of strain sensors can be used to evaluate safety in operating periods of bridges. However, most of the published researches about distributed deformation monitoring are focused on solid rectangular beam rather than box girder—a kind of typical hollow beam widely employed in actual bridges. Considering that the entire deformation of a single-cell box girder contains not only bending deflection but also two additional deformations respectively caused by shear lag and shearing action, this paper again revises the improved conjugated beam method (ICBM) based on the LFBG sensors to satisfy the requirements for monitoring two mentioned additional deformations. The best choice for the LFBG sensor placement in box gilder is also proposed in this paper due to strain fluctuation on flange caused by shear lag effect. Results from numerical simulations show that most of the theoretical monitoring errors of the revised ICBM are 0.3%~1.5%, and the maximum error is 2.4%. A loading experiment for a single-cell box gilder monitored by LFBG sensors show that most of the practical monitoring errors are 6%~8%, and the maximum error is 11%.

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Measurement of the Thermal Expansion for Space Structures Using Fiber Bragg Grating Sensors and Displacement Measuring Interferometers

Smart Materials, Adaptive Structures and Intelligent Systems, Volume 1 ◽

10.1115/smasis2008-479 ◽

2008 ◽

Author(s):

Hong-Il Kim ◽

Lae-Hyong Kang ◽

Jae-Hung Han

Keyword(s):

Fiber Bragg Grating ◽

Real Time ◽

Deformation Monitoring ◽

Space Environment ◽

Space Structures ◽

Bragg Grating ◽

Environment Change ◽

Time Deformation ◽

Fiber Bragg Grating Sensors ◽

Fbg Sensors

Dimensional stability of the space structures, such as large telescope mirrors or metering substructures, is very important because even extremely small deformations of these structures might degrade the optical performances. Therefore, precise deformation data of the space structures according to environment change are required to design these structures correctly. Also, real-time deformation monitoring of these structures in space environment is demanded to verify whether these structures are properly designed or manufactured. FBG (fiber Bragg grating) sensors are applicable to real time monitoring of the space structure because they can be embedded onto the structures with minimal weight penalty. In this research, therefore, thermal deformation measurement system for the space structures, composed of FBG sensors for real time strain measurement and DMI (displacement measuring interferometers) for accurate specimen expansion data acquisition, is developed. Thermal strains measured by distributed FBG sensors are evaluated by the comparison with the strains obtained by highly accurate DMI.

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