The LASS System: Structural Health Monitoring By Large Area Strain Detection

Abstract

A dense and well-maintained infrastructure is a necessary part of any modern nation. However infrastructure surveillance is a non-trivial problem. Structural health monitoring (SHM) would ideally entail frequent structure surveillance, in order to rapidly detect new material failures such as crack formation. This structural surveillance is often overlooked in many first world nations, the United States included. Often bridge inspections happen every 2 years [1]. This motivates deeper research into the field of SHM with the goal of making surveillance both cheaper and more effective. One way to improve current SHM methods is to monitor strain on the surface of urban structures. Changes in strain can help to predict future material failure. The system described here is designed to be easy to apply, minimally intrusive, and highly sensitive to changes in surface strain. It accomplishes all this while being sufficiently portable and power efficient, thus making it easy to use. This Large Area Strain Sensing system, or LASS, is designed on two PCBs–one flexible for adhesion to the surface and one rigid for signal multiplexing, amplification and power supply. This hybrid system design offers flexibility and sensing over large areas, while using high performance devices on traditional silicon substrates to read these sensors with higher accuracy than could be achieved on thin film transistor-based ICs [2]. Sensor output signal is acquired using a USB connected data acquisition device (DAQ). This system has been assembled and lab tested with collaboration from Professor Glisic and the Structural Health Monitoring Lab. Comparative testing of adhesives found a suitable adhesive in araldite for non-destructive strain testing on the structure surfaces. The LASS system shows resolution down to 23 μe in short term tests and stability within +/- 15 μe over the course of multiple days. The LASS system has been shown to be effective at localizing small area strain, like the strain produced by a crack opening. Finally the LASS has been field tested on Streicker bridge, a footbridge with relatively high pedestrian traffic.