Spiral Deployment of Optical Fiber Sensors for Distributed Strain Measurement in Seven-Wire Twisted Steel Cables, Post-Tensioned against Precast Concrete Bars

Abstract

On-time monitoring and condition assessments of steel cables provide mission-critical data for informed decision making, ensuring the structural safety of post-tensioned concrete structures. This study aimed to develop a spiral deployment scheme of distributed fiber optic sensors (DFOS) and to monitor/assess the post-tensioned force in seven-wire twisted steel cables, based on the pulse-pre-pump Brillouin optical time domain analysis. Each DFOS was placed in a spiral shape between two surface wires of a steel cable and glued to the steel cable by epoxy. Image observations were conducted to investigate the entireness and bonding condition between the optical fiber and the steel wires. Eight concrete bar specimens were cast, each with a pre-embedded plastic or metal duct at its center and each was post-tensioned by a steel strand through the duct once they were instrumented with two strain and two temperature sensors. The strand was loaded/unloaded and monitored by measuring the Brillouin frequency shifts and correlating them with the applied strains and the resulting cable force after temperature compensation. The maximum, minimum, and average cable forces integrated from the measured stain data were compared and validated with those from a load cell. The maximum (or average) cable force was linearly related to the ground truth data with a less than 10% error between them, after any initial slack had been removed from the test setup. The post-tensioned force loss was bounded by approximately 30%, using the test setup designed in this study.

Experiment of the monitoring prestress loss of prestressed concrete beams with damages under static loading

“…In order to ensure the synergistic deformation of the smart rebar and the outer wire of the ordinary steel strand, several layers of high-ductility metal sheets (the 0.02 mm copper foil is used in this study) are wrapped on the surface of the smart rebar, the interlayer friction between the smart rebar and the outer wire of ordinary steel strand is improved by increasing the diameter of the smart rebar. With the help of the steel strand's end anchoring and torsion effect under stress, the smart rebars will be naturally wrapped to make the effect of synergistic deformation [17][18][19][20].…”

Hybrid Distributed Optical Fiber Sensor for the Multi-Parameter Measurements

“…Brillouin scattering light is characterized by the linear relationship with strain and temperature in the frequency domain [ 72 , 73 , 74 , 75 , 76 , 77 ]. The Brillouin scattering-based DOFSs are particularly competent in the structural health monitoring of oil and gas facilities [ 78 , 79 , 80 , 81 , 82 , 83 , 84 ], power grids [ 83 , 85 , 86 , 87 , 88 , 89 , 90 ], tunnels, bridges, and pavements [ 91 , 92 , 93 , 94 , 95 , 96 , 97 ]. Meanwhile, geological disaster prewarning [ 98 , 99 , 100 , 101 , 102 ] and geophysical engineering [ 103 , 104 , 105 ] are also application targets.…”