Monitoring Early-age Strain and Temperature Distributions in Full-scale Steel-concrete Composite Beams with Distributed Fiber Optic Sensors

Abstract

Concrete is subject to temperature gradients and shrinkage-induced strain during curing. Strain variations in concrete can lead to residual stresses and cracks, in particular when the deformation of concrete is restrained. This in turn can affect the mechanical performance and durability of the structure. In this study, a fullydistributed fiber optic sensor is used to monitor the early-age temperature and strain distributions in a 12.8 m long steel-concrete composite beam based on pulse pre-pump Brillouin optical time domain analysis. Telecommunication-grade, single-mode optical fibers were embedded in the concrete of the specimen that consisted of lightweight aggregate concrete on trapezoidal metal deck acting compositely with a steel I-beam via headed shear studs. Emphases were placed on characterizing the temperature and strain distributions in concrete and understanding the effects of composite action on the evolution of strains in the concrete. Non-uniform strain distributions were successfully measured from the distributed fiber optic sensors in the first two days of curing. The spatial distribution of temperatures along the beam was relatively uniform but varied in amplitude due to the hydration reactions. The strain distributions were non-uniform, which is likely due to concrete cracking as the result of restrained shrinkage of the concrete.