In late 2008, a fiber optic structural health monitoring (SHM) system was installed on the Chiapas Bridge in Mexico. This installation represents the first SHM instrumented bridge in Mexico using optical fiber sensors and SHM techniques. The project was conceived and managed by the Structures Department within the Institute of Engineering at the National Autonomous University (UNAM) in Mexico, under contract from the Mexican Transportation Undersecretary. The system was designed by MCH Engineering LLC, equipment and sensors provided by Micron Optics Inc. and the system installed by Chandler Monitoring Systems Inc. (www.chandlermonitoring.net).

Figure 1: Aerial view of the Chiapas Bridge in Southwest Mexico

The Chiapas bridge was opened to traffic in 2003 and is the most important structure of an entire highway going through the state of Chiapas, in Southwest Mexico, and part of the Transamerican highway system. The superstructure is a continuous grade 50 steel orthotropic box of constant height comprising 8 spans, with a total length of 1208m. Piers heights range from 27 to 89 m measured from the bottom of the dam. Steel jackets of the offshore type, were used as the main elements of the piers.

Figure 2: Aspect and topology of the installed sensor network inside the bridge

During construction of the superstructure, a basic monitoring system was initially implemented to monitor and assess the structural behavior of the bridge. However, advances in SHM techniques and the importance of the Chiapas Bridge in the region, prompted the need for a new and advanced instrumentation system. The new solution is based on a multi-point, multi-sensor monitoring system based on optical fiber Bragg grating sensors and opto-electronic interrogators. The system is self contained, works as a stand-alone equipment and allows for the in-situ, real-time monitoring of the bridge as well as its long-term condition. A total of 82 fiber optic strain and temperature sensors were installed in key bridge locations. Local electric power is supplied by a solar panel system.

The monitoring system instrumentation is composed of a single optical interrogator (Micron Optics model sm130-500) with 4 optical channels, scanning at 1khz; a 4×16 channel sensor multiplexer (model sm041-416) and a sp130 controller and data acquisition module (Figure 3). The system can be configured to record data at any specific interval and to any threshold level.

Figure 3: Micron Optics Interrogation System on Chiapas Bridge

Admin edited to add images 4/6/09