<title>Structural damage monitoring in composite-confined concrete columns using Bragg gratings</title>

Abstract

Confinement of concrete columns for earthquake retrofit and new construction is being studied extensively and has been implemented in some applications. Large-scale, composite- confined concrete cylinders were tested to failure in compression to investigate scale effects on the response of the material, to allow more thorough instrumentation, and to study the feasibility of long-term monitoring of composite civil structures using embedded sensors. Bragg grating optical fiber strain gages were embedded in three hoop-wrapped, filament-wound, carbon/epoxy composite cylinders. Multiple optical fiber gages were placed in both the axial and circumferential directions. Resistive gages were placed near the optical fiber locations. The 12-inch diameter cylinders were filled with concrete and tested in axial compression. A triaxial state of strain was induced in the optical fibers -- axial compression from the load, radial pressure from the expanding concrete, and circumferential tension to contain the radial pressure. The extensive data recorded in the optical fiber and resistive strain gages during compression loads to failure allowed a detailed study of transverse strain effects on Bragg gratings. Conventional mechanics of materials models and micromechanical finite element models were used to predict the relationship between surface strains measured by resistive gages and Bragg grating wavelength shifts. Various models were used to account for the effects of the three strain components on the response of the Bragg grating. Although the average error between resistive and optical fiber readings could be reduced by correcting for transverse strains, there were still significant differences (over 20%). The embedded optical fiber strain gages did provide a sufficiently repeatable and accurate measurement of strain in these structures for long- term damage monitoring or post-earthquake inspection.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.