Structural Monitoring, Sandia National Laboratories Develop Infrastructure Sensors

Sandia National Laboratories and Structural Monitoring Systems PLC have outfitted a U.S. bridge with a network of eight real-time sensors able to alert maintenance engineers when the sensors detect a crack or when a crack reaches a length that requires repair.

Sandia National Laboratories mechanical engineer Stephen Neidigk positions a comparative vacuum monitoring sensor on a bridge. In his other hand is the control system that periodically checks the sensor and wireless transmitting device that alerts maintenance engineers if it detects a crack. Courtesy of Randy Montoya.

The goal of structural health monitoring is to increase supervision of critical areas, extend the lifetime of structures, and ultimately reduce operating costs and improve safety.

In 2016, more than 54,000 bridges in the U.S. were classified as “structurally deficient” by the Federal Highway Administration's National Bridge Inventory. This means about 9 percent of U.S. bridges need regular monitoring.

“Areas that are difficult to access or things that are remotely located like bridges, pipelines, and other critical structures present significant challenges to properly monitoring the health of the structure or equipment,” said Dennis Roach, senior scientist at Sandia. “A network of structural health monitoring sensors could be a solution or at least help ensure the necessary vigilance over these components.”

The structural health monitoring system for the trial bridge consists of eight comparative vacuum monitoring sensors, a vacuum pump to form the vacuum, a control system, and a wireless transmitting device that calls or texts maintenance engineers if a sensor detects a crack. The whole system is powered by a lithium ion battery, which is recharged by a solar panel.

The comparative vacuum monitoring sensors produced by Structural Monitoring Systems are made of thin, flexible Teflon and have rows of little channels called galleries. They can be stuck onto critical joints or welds or placed near other places cracks are likely to form. When the metal is whole, the pump is able to remove all of the air out of the galleries, forming a vacuum. When a tiny crack forms in the metal underneath the sensor, it can no longer form a vacuum, similar to how a vacuum cleaner stops working when the hose has a leak. These sensors can detect cracks smaller than the thickness of a dime.

“In 15 years of testing comparative vacuum monitoring sensors, they have achieved a tremendous track record for producing dependable structural health monitoring,” said Tom Rice, the mechanical test engineer at Sandia in charge of testing various structural-health monitoring systems. “Once they get incorporated into more systems, in areas of concern, it's just going to make aircraft, trains, and bridges safer as time goes on."

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration. Structural Monitoring Systems develops technology to monitor and test the structural integrity of various materials, products, and entities.