Strain measurements on concrete beam and carbon fiber cable with distributed optical fiber Bragg grating sensors

We report on civil engineering applications of wavelength multiplexed optical fiber Bragg grating arrays directly produced on the draw tower for testing and surveying advanced structures and materials such as carbon fiber reinforced concrete elements and prestressing cables. We equipped a 6×0.9×0.5 m concrete beam, which was reinforced with carbon fiber reinforced epoxy laminates, and a 7‐m long prestressing carbon fiber cable made of seven twisted strands, with optical fiber Bragg grating sensors. Static strains up to 8000 μm/m and dynamic strains up to 1200 μm/m were measured with a Michelson interferometer used as Fourier spectrometer with a resolution of about 10 μm/m for all sensors. Comparative measurements with electrical resistance strain gauges were in good agreement with the fiber optic results. We installed the fiber sensors in two different arrangements: some Bragg grating array elements measured local strain while others were applied in an extensometric configuration to measure moderate strain over a base length of 0.1 to 1 m.