<title>Fiber optic sensor system for bridge monitoring with both static load and dynamic modal sensing capabilities</title>

Abstract

Abstract We describe a fiber optic Bragg grating distributed strain sensor system for large scale structuralmonitoring applications, such as bridge monitoring. The system is capable of assessing both longterm static structural loading changes and dynamic/modal behavior of the structure using twodifferent optical interrogation schemes to address the same sensor array. The system has beenused to monitor over 45 sensors attached to or embedded in a single-lane bridge span, for damageassessment. 1. INTRODUCTION Fiber Bragg grating (FBG) sensors are rapidly being adopted in a variety of sensing applicationsdue to their unique potential for multi-point, or distributed, sensing capabilities. These sensors posses a number of unique advantages when compared to their conventional counterparts, including immunity to EMI, absolute strain sensing capability, ease of multiplexing [1], andcompatibility with being embedded in a range of structural materials. FBGs are wavelengthencoded sensors: strain information obtained from the devices is contained within the reflectedwavelength components. This advantageous feature of the FBG elements simplifies the process ofmultiplexing a large number of elements on a single fiber strand. The multiplexed devices can bewritten with different spectral characteristics that can be correlated to the physical location of eachdevice along the fiber. Any wavelength shifts of a particular device can be attributed to the 1 strainat the location of that sensor and a quasi-distributed strain sensor system can be created with aminimum of optical fibers. Much of the recent work in the field has focused on the development of