Long-term monitoring of a reinforced concrete highway bridge using vibrating wire sensors – University of São Paulo

by: Alberto B. Colombo
Location: Fernão Dias Highway near the city of Extrema in the Brazilian state of Minas Gerais


INTRODUCTION
This project, carried out by researchers of the University of São Paulo, consists of a long-term monitoring of a reinforced concrete bridge using vibrating wire sensors. The monitored bridge is located in the Fernão Dias Highway near the city of Extrema in the Brazilian state of Minas Gerais.
The goal of this system is to detect the effects of structural degradation through the monitoring of strains and displacements. Reinforcement corrosion is a major issue with respect to reinforced concrete structures. A loss of crosssectional area due to corrosion generates a reduction of stiffness for the affected sections of the structure. This loss of stiffness will cause increase in strains and displacements due to the dead loads acting on the structure. Using an effective monitoring system these variations can be detected. Through advanced analysis models a maintenance plan can be developed.

Geokon VW sensor to measure concrete Strains Cross view to show it's location

Geokon VW sensor to measure concrete Strains
Cross view to show it’s location


THE MONITORING SYSTEM

The monitoring system is comprised of 41 Geokon vibrating wire sensors distributed over three out of five of the bridge’s spans. Three crosssections were instrumented with vibrating wire strain gauges in order to determine the evolution over time of the section’s strain profile. Displacement transducers were also used to measure the mid-span deflections, the elastomeric bearings’ displacements and movements across surface cracks.A Campbell Scientific CR1000 was used for logging data. The vibrating wire sensors are read using de AVW200 vibrating wire analyzer. The sensors are linked to the datalogger through three multiplexers, which are distributed throughout the bridge.

Displacement at Elatomeric Bearing

Displacement at Elatomeric Bearing


WEB-BASED DATA VISUALIZATION

A web interface to visualize the collected data was needed and Vista Data Vision software was selected. VDV allowed the researchers to quickly configure a data management and visualization system. In a long term monitoring systems such as this a web interface is very important. Bridge owners will often want to have an easy access to the collected data, as well as the engineers that are responsible for the monitoring system.
The data management and analysis tools that are built in VDV (alarms) are also very important for these types of systems. The alarms may indicate a sensor malfunction or the occurrence of structural damage. The ability to detect and inform the occurrence of structural damage is one of the main objectives of this type of system.With VDV a web page with plots of the measured variables of interest was created. The software also allows for the creation of information pages which were used to put a description of the installed system online.

Figure_2

Plots showing measured Displacement at Elatomeric Bearings Dual Axis with temperature readings on the right axis


Figure_3

Information pages with a description of the monitoring system.

CONCLUSION

This was the first long-term bridge monitoring system to be installed in Brazil and the experience gained by the participants of this project is invaluable. This project was quite challenging because it require the integration of several different knowledge areas, such as, instrumentation electronics, computing and structural engineering. With the knowledge gathered during this project, the research group hopes to be able to take on similar bridge projects in the country.
Overall the project was considered to be a success. The monitoring system is collecting data which is used by researchers from the University of São Paulo. There is still much work to be done in data managing and analysis, and the system will continue to be adjusted in order to fix any issues that arise. The data analysis process will generate several research papers, which will be able to demonstrate to the scientific community the importance of such projects.

Underneath the bridge

Underneath the bridge