ABSTRACT

CONTENTS 21.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584 21.2 Background on Electrical Resistance-Based Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585 21.3 Electrical-Resistance Strain Gages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585 21.4 Signal Conditioning for Electrical-Resistance Strain Gages . . . . . . . . . . . . . . . . . . . . 587 21.5 Large-Strain Binary-Output Resistance-Based Sensors . . . . . . . . . . . . . . . . . . . . . . . . . 590 21.6 Data Acquisition and Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594

21.6.1 Passive RFID Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594 21.6.2 Mote-Based Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595

21.7 Control Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597 21.7.1 Installation and Sensor Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597 21.7.2 Configuration of Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 598 21.7.3 Data Logging and Presentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 599

21.8 CRM Gage Functionality Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 599 21.8.1 Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 601

21.9 Full-Scale Deployment of CRM Gage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602 21.10 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605

Automated structural “health” monitoring (SHM) seeks to assess continuously the integrity of building structures using a set of embedded sensors. In this chapter, we discuss the use of resistance-based strain gages in SHM applications, where the gages are used to measure changes in one or more dimensions of a critical structural element. We also present a binary gage designed to detect unequivocally cracks of widths exceeding a predetermined threshold. The binary gages can be used to map damage directly without complex data analysis and correlations between the data reports, structural analysis results, or information on structural drawings. In terms of network requirements, binary gage data reports have a low data rate and are naturally resilient to data loss. We discuss how commercial off-the-shelf (COTS) data acquisition and communication devices can be used to build a multi-hop wireless SHM network. The SHM network is low cost, configurable, and amenable to flexible and clutter-free deployments.