About The Bridge
The Chiapas Bridge is a steel bridge over a kilometer in length which spans the Nezahualcoyotl or Malpaso Dam in northern Chiapas, Mexico. It is 1,208 meters long and 8 meters wide connecting Veracruz and Chiapas Mexico. Construction of the bridge began in 2002 and finished fourteen months later, voted the best infrastructure project in Mexico in 2004. Its exact location is Km 961 of the Coapas-Ocozocoautla highway and cuts the travel time from Mexico City to Chiapas by roughly 3.5 hours. It makes the rural area in northern Chiapas more accessible and open to ecotourism.
The bridge is ten meters wide, with eight supports, seven pillars or “jackets” and one strip of concrete fastened onto solid land. The upper part of the bridge is made of orthotropic materials with 102 metal voussoirs which weigh 8,900 tons with an average weight of eight tons per meter. The total amount of steel used is over 19,000 tons, the equivalent of four ocean oil platforms.
The objective to monitor the integrity and behavior of the bridge structure, and the kinds of effects caused by high traffic and heavy loads that may damage and fatigue the bridge. There are strain and temperature sensors in 16 zoned locations. When multiple heavy truck traffic was present the bridge at times would lift from pier's due to a wave effect in the bridge length not able to expand properly. The optical monitoring system being passive allowed an internal festoon optical trunk cable with periodic splice trays to tap into the cable to feed to sensors to the centralized control panel. Information of these effects to structurally solve after sufficient information was gathered to increase bridge expansion and contraction capabilities.
The installation to implement the fiber optic structural health monitoring (SHM) system 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 a turnkey engineering and installation provided by ChM4 Inc. While deploying the system jointly with UNAM trained by ChM4 to learn techniques used for optical sensing systems and to assist in our installation efforts. MCH Engineering coordinated the relationships with Luna and UNAM for this SHM opportunity.
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 Luna 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 Luna optical interrogator, scanning at 1khz; a Luna 4×16 channel sensor multiplexer and a sp130 controller and data acquisition. The system can be configured to record data at any specific interval and to any threshold level.
Layout of Chiapas sensor locations and cross section placement
Pictures of control panel with Luna equipment and solar power arrangement is shown. Due to the Chaipas Bridge remote location this was the only source of power.
ChM4 pictures of structural health monitoring installation of FBG optical sensors at Chiapas Bridge and training of UNAM students. Examples are shown of our kitting methods one of the keys to our success.