Theta Enables Smart Monitoring for the World’s Longest Three-Tower Cable-Stayed Bridge

Over time, the preloading force of cable clamp bolts on suspension bridges can gradually weaken. Loss of tension may lead to clamp slippage, deformation of structural alignment, and failure of the cable dehumidification system. In January 2022, China’s Ministry of Transport issued the Technical Specification for Structural Health Monitoring of Highway Bridges, which explicitly requires real-time monitoring of cable clamp and high-strength bolt preloads.

Theta recently completed the deployment of an online monitoring system for cable clamp bolts on a major Yangtze River highway bridge — the world’s longest three-tower, double-main-span cable-stayed bridge, spanning over 36.274 km with pylons over 300 meters tall. The project adopted Theta’s proprietary SAS100 wireless bolt preload sensor, which transmits real-time data via Ethernet to the client’s monitoring platform. The system provides continuous insight into bolt tension and loosening trends, triggering timely warnings and alerts.

The SAS100 is a non-intrusive, wireless ultrasonic sensor mounted on one end of the bolt. It emits ultrasonic waves through the bolt, measures flight time differences, and determines elongation and preload levels using advanced signal processing and temperature compensation algorithms. It can even identify bolt fractures and their locations.

With no wiring required and ultra-low power consumption, the SAS100 offers a battery life of over 10 years, making it ideal for long-term bridge monitoring applications.

The system has now been successfully installed and commissioned, marking a major step forward in the bridge’s smart monitoring upgrade — with Theta continuing to deliver innovation across critical infrastructure projects.