A Real-Time Monitoring System for Cable Tension with Vibration Signals Based on an Automated Algorithm to Sieve Out Reliable Modal Frequencies

Abstract

Cables or suspenders are the critical force-transmitting components of cable-supported bridges, and their timely tension monitoring is consequently the most important issue in the corresponding structural health monitoring. However, very few works regarding the full automation of vibration-based tension estimation have been reported in the literature. To develop a monitoring system of cable tension based on real-time vibration signals, this research first employs an efficient stochastic subspace identification (SSI) method with tailored parameter selection to continuously identify the three frequencies of adjacent modes for the cables of Mao-Luo-Hsi Bridge. More importantly, an automated sieving algorithm is delicately established to obtain the stable modal frequencies by making the best of the specific modal frequency distribution for cables. The ratios between the frequency values identified from SSI analysis are exhaustively checked to systematically extract the qualified cable frequencies and decide their corresponding mode orders. The tension is finally computed with one available cable frequency according to the priority order predetermined by the statistics of identification rate. Demonstrated by analyzing the vibration signals measured from the stay cable of Mao-Luo-Hsi Bridge in real time for two full years, the effectiveness and robustness of this real-time monitoring system have been extensively testified. The long-term success rates for the immediate determination of dependable tension are found to be perfect for 15 of the 18 investigated cables. As for the other three cables, their corresponding success rates are still higher than 99.99% with very few cases of absent or false tension values.

Unveiling Structural Secrets: Active Learning for Assessing Ultimate Load Capacity in Parallel Wire Cable Systems under Time-Varying Force Identification with Frequency-Squeezing Processing and Vibration Frequency Method

“…Influenced by bending stiffness, support conditions, and concentrated mass, VFM involves the derivation of the cable vibration equation and the establishment of the mapping relationship between the cable tension and the natural frequency. It is imperative to acknowledge the presence of several assumptions inherent in the analysis of the vibration equations, including the uniform distribution of cable mass with equal cross-section and material elasticity, and the exclusion of rotational inertial mass, shear deformation, and the sag effect [21]. Hence, by incorporating considerations of bending rigidity, end support conditions, and centralized mass in the span, a unified equation is formulated to delineate the relationship between the cable force and the fundamental frequency of the cable:…”

“…Additionally, the use of thin rod vibration sensors with high-sensitivity Fiber Bragg grating (FBG) technology allows for accurate cable force measurements, even in challenging scenarios like measuring forces in steel strand-type bracing cables [20]. Automation of vibration-based tension estimation through stochastic subspace identification (SSI) methods further improves accuracy by continuously identifying stable modal frequencies and efficiently computing cable tensions in real time [21]. By integrating these advancements, cable force identification in cablestayed bridges becomes more reliable and effective, ensuring the structural integrity and long-term serviceability of the bridges.…”

Enhancing stress measurements accuracy control in the construction of long-span bridges

“…Among the devices used for direct stress measurement are load cells 11,12 , fibre optic Bragg grating sensors 13 or elastomagnetic strain sensors 14,15 . While the most common indirect methodology for rapid stress assessment in bridge cables is the vibrating wire technique [16][17][18] .Another important parameter to be monitored during construction operations is the structural response of the auxiliary elements used for their construction, such as the temporary stay-cable towers used in bridges built using the successive cable-stayed cantilever technique. In the configuration of these auxiliary towers, it may be common to embed them in the base by means of a prestressed connection, using short prestressing units.…”

“…Among the devices used for direct stress measurement are load cells 11,12 , fibre optic Bragg grating sensors 13 or elastomagnetic strain sensors 14,15 . While the most common indirect methodology for rapid stress assessment in bridge cables is the vibrating wire technique [16][17][18] .…”