Monitoring the Structural Health of the Rion-Antirion Bridge Using LabVIEW Real-Time - Solutions

Advitam uses the power of virtual instrumentation to monitor the integrity of the Rion-Antirion Bridge, which is nearly 10,000 feet long and subject to harsh environmental conditions.

Author(s):
Bernard Basile - Advitam, Inc.

Industry:
Basic Materials - Steel/ Lumber/ Construction

Products:
PXI/CompactPCI,

The Challenge:
Developing a structural monitoring system to measure and define the behavior of the Rion-Antirion Bridge during normal operation, strong winds, and earthquakes.

The Solution:
Using a combination of four PXI/SCXI chassis linked with National Instruments LabVIEW Real-Time software to incorporate the conditioning, acquisition, processing, control, storage, and sharing of measurements.

"This system is fully functional and the customer is extremely satisfied. It has already inspired a similar monitoring system for the Millau Viaduct in France. We will continue to optimize the system, and we intend to offer customized versions for other monitoring systems in the near future"

At Advitam, a subsidiary of Vinci Construction, we develop asset management, civil engineering, and structural monitoring services with a focus on occurrence detection and risk analysis methods. With this unique experience, Advitam was in charge of the design and implementation of a structural monitoring system for the Rion-Antirion Bridge, which spans the Corinth Strait and links Peloponnese in southern Greece to the Greek mainland. At 2,883 meters (9,458 feet) long, the bridge is frequently exposed to heavy lateral wind forces. It is also located in an area of high seismic activity, with each end on different tectonic plates, resulting in a relative movement of almost two centimeters per year.

The challenge was to design a monitoring system that could operate in this harsh environment while providing a reliable, continuous data stream to record measurements and events that can affect the bridge’s structural integrity.

Implementation

The project started three years before the bridge opened and began with a risk analysis to define which elements of the bridge were critical and in need of monitoring. Advitam identified which sensors were required, as well as where they should be placed on the bridge. These included:

3D accelerometers on the deck, pylons, stay cables, and on the ground to characterize wind movements and seismic tremors
Strain gages and load cells on the stay cables and their gussets
Displacement sensors on the expansion joints to measure the thermal expansion of the deck
Water-level sensors on the pylon bases to detect infiltration
Temperature sensors in the deck to detect freezing conditions
Linear variable differential transducer (LVDT) sensors on the stay cables to measure movement
Load cells on the restrainers for recalibration in the event of an earthquake
Two weather stations to measure wind intensity, direction, air temperature, and relative humidity

With the addition of a power supply and a lightning conductor control, the required system needed a total of 372 measurement channels. It also had to be capable of acquisition and simultaneous, dynamic processing of multiple signals for the purpose of permanent monitoring, while presenting a user-friendly interface and well-designed output reports. Given the large number of input channels and the adverse operational environment, we chose the National Instruments PXI/SCXI chassis housing National Instruments LabVIEW Real-Time software to perform the task. The resulting system houses and performs the following tasks with a high degree of reliability:

Signal conditioning
Data acquisition
Data processing
Program control
Data storage
Data transmission

Each of the bridge’s four pylons is equipped with an NI PXI-1010 chassis (with eight PXI slots and four SCXI slots) equipped with an NI PXI-8175 controller, SCXI signal conditioning modules linked to the sensors, an NI PXI-6040E module to acquire the data, and an NI PXI-8423/2 module to integrate (in RS485) the data from the weather station. NI LabVIEW Real-Time software runs on each PXI controller to ensure the acquisition and scaling of the measurements, comparing them to fixed or variable thresholds to trigger alarms if necessary. The four systems are linked through a fiber-optic Ethernet network to a control PC installed in the operations building.

Each PXI device continuously acquires data and creates history files that are regularly sent to the control PC. When a threshold goes past its limit, a selective acquisition unit with real-time recording is started on each chassis. A pre-trigger mechanism is also incorporated to identify and record the events that occurred immediately before the alarm.

The interface on the control PC offers different windows to the user, including a synoptic view of the bridge that shows measurement points. Those points are typically displayed in green, but change to red when a threshold goes past its particular limit. The interface also includes automatic and expert function analysis. We can remotely access the computer via a modem to access information or to redefine monitoring parameters.

This system is fully functional and the customer is extremely satisfied. It has already inspired a similar monitoring system for the Millau Viaduct in France. We will continue to optimize the system, and we intend to offer customized versions for other monitoring systems in the near future.

For more information, please contact:

Bernard Basile

Advitam

1 bis, rue du Petit Clamart

BP 102

78143 Velizy Cedex

France

Tel: +33 1 01 46 01 85 00

E-mail: bbasile@advitam-group.com

Or, within the U.S., contact:

John Stieb, P.E.

Advitam, Inc.