Project detail

HIGHWAY BRIDGE EXTERNAL TENDONS

Type of structure

Bridge

Location

Italy

Why monitoring

  • Assess the structural behaviour induced by traffic vibrations on the bridge
  • Detect early warning signs of corrosion of the tendons
  • Evaluate in real-time the strands condition during the service life of the structure
  • Set thresholds values to the expected tendon vibrations levels to preserve the safety service conditions
  • Plan effective maintenance interventions

Interventions in synthesis

  • Type of devices : Accelerometers
  • Installation time : September 2017
  • Analyzed data : Acceleration

Goals

External pre-stressing is increasingly being used especially in motorway bridge structures due to the substantial savings in terms of construction time. The deterioration or breakage of internal or external tendons can be catastrophic for the entire structure. For this reason, real time monitoring of pre-stressing tendons should provide useful information to detect possible fatigue and damage/deterioration processes.

A high performance and cost-effective SHM system of MEMS accelerometers has been installed on a highway concrete bridge located in the center of Italy. The bridge has been instrumented with a continuous monitoring system of 88 triaxial accelerometers for the real-time detection of the external tendons strands condition during the service life of the structure.

The service life of tendons in pre-stressed structures depends on the behaviour of the steel strands that compose them. Application of MEMS accelerometers can thus provide structure owners with a measure of the fundamental properties necessary to predict the long-term performance of the bridge. In particular, changes in the dynamic characteristics of the monitored elements have been analysed by detecting the shift in tendons’ natural frequencies. A specific data processing algorithm has been developed in order to analyse the collected sensors' data and provide an efficient real time tendon monitoring. The trends observed during the monitored period allowed defining a benchmark of measurements corresponding to the standard behaviour of pre-stressing tendons subject to traffic conditions or non-exceptional external loads.

Several sets of data under regular traffic excitation have been collected and, consequently, threshold levels (attention/alarm) have been defined for the monitoring system. The monitoring system is also able to control the bridge response after accidental actions, like earthquakes with epicentre in adjacent regions.