Abstract:A normal cable force state of a suspension bridge is extremely vital to bridge safety. For cable force monitoring of already completed suspension bridges, it is not suitable to conduct direct parameter measurements by modifying the anchor cable structure of the bridge. Instead, using an indirect measurement would not destroy the bridge's original structure and also meet engineering requirements. In this paper, a fiber Bragg grating (FBG) vibration sensor was developed for online monitoring of the cable vibration characteristics of Tongwamen bridge. The monitored vibration frequency was converted into cable force according to the theory of string vibration, so as to achieve an indirect measurement of bridge cable force. On both north and south sides of the bridge, FBG vibration sensors were mounted symmetrically on 8 of 19 cables for distributed measurement. The forces of two cables were found to be abnormal, which was considered worthy of attention and close inspection. This result is of great significance for the structural monitoring and safe operation of Tongwamen bridge.

The application of acrylonitrile-butadiene-styrene (ABS) copolymer as construction material is largely restricted by its inherent flammability and the release of a great amount of smoke and toxic gases during combustion. To address this issue, the combination of conventional flame retardants and nanoadditives was proven to be a promising way. Herein, both intumescent flame retardants (IFR) and layered nanofillers, that is, graphene and layered double hydroxide were added into ABS resin. These nanofillers exhibited superior dispersion in the ABS matrix. Thermal and fire behaviors of ABS resin were investigated by thermogravimetry analysis, UL-94 vertical burning test, limiting oxygen index test, and cone calorimetry. The ABS composites containing IFR and layered nanofillers presented remarkable decline in total heat release, peak heat release rate, and volume of toxic effluents released in the burning process compared with those of neat ABS, indicating the significantly improved fire safety of ABS. Moreover, introducing layered nanofillers could further enhance the heat stability and fire safety of the flame-retardant ABS composites, indicating the presence of synergistic effect between IFR and layered nanofillers. The scanning electron microscopy and Raman spectroscopy results confirmed the formation of compact and dense intumescent chars, which could obstruct the spread of heat and mass, and thus improved the heat stability and flame retardancy of ABS resin.

This paper describes the structure design, parameters optimization, and performance test of a fiber Bragg grating strain sensor with features of surface-mounting and reusability. Flexure hinges are adopted in the design of a key elastic body. Number of mounting holes, sealing, sensitization, and stiffness of the sensor have been considered and optimized. Then, sensor prototype has been manufactured and fully tested. The experimental results show that the stiffness and the sensitizing coefficient are identical to design the values. Test results also show that the sensor provides a sensitivity of 3.357 pm/με with a fitting linear correlation coefficient of 0.9999, a measurement range of ±600με, a repeatability error of 2.73%, and a hysteresis error of 4.67%. Furthermore, good creep resistance and good capability for alternating strain measurement have also been demonstrated. These results promise the sensor potential applications in structural health monitoring.

The main innovation of this work is to achieve resource recycling and environmental pollution control, and obtain flame retardant TPU composites with high added value simultaneously.

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