# Microwave Radar-Based Cable Displacement Measurement for Tension, Vibration, and Damping Assessment

## TL;DR

Microwave radar is used to measure cable displacements in bridges, helping assess tension, vibration, and damping without contact sensors.

## Contribution

A non-contact microwave radar method is introduced for cable displacement measurement and damping assessment in bridges.

## Key findings

- Microwave radar effectively measures cable displacements while eliminating low-frequency deck motion effects.
- The method enables direct vibration characterization and improved damping evaluation through free-decay testing.
- Field tests on two cable-stayed bridges validated the effectiveness of the radar-based approach.

## Abstract

Cables in cable-supported bridges are critical structural components with exceptional tensile capacity, and their assessment is essential for the safety of both the cables themselves and the entire bridge. Microwave radar, a non-contact and efficient measurement technique, has emerged as a promising tool for bridge cable evaluation. This study demonstrates the deployment of microwave radar on bridge decks to efficiently measure the displacements of multiple cables, enabling coverage of all cables while effectively eliminating low-frequency components caused by deck deformation and radar motion using the LOWESS method. The measured cable displacements can be directly used to characterize vibrations, particularly for detecting vortex-induced vibrations (VIVs), without the need for numerical integration of accelerations. Furthermore, microwave radar is applied to free-decay testing for cable damping evaluation, providing an improved signal-to-noise ratio and eliminating the need for sensors installed via elevated platforms, thereby enhancing the reliability of damping assessments. The effectiveness of these approaches is validated through field testing on two cable-stayed bridges.