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Estimation of distributed rotation angles of steel and concrete beams using fiber optic strain sensors

This article presents a reference-free strategy for monitoring distributed rotation angles along the steel and concrete beams based on fiber optic strain sensors. Firstly, moment-curvature analysis shows that distributed rotation angles of steel beams can be theoretically estimated by measured long-gauge strain. Meanwhile, the modified approach for reflecting the effect of randomly appeared cracks of concrete beams on neutral axis position is also established. Then, numerical simulation of several beams with different boundary conditions and load types is conducted, and simulation results indicate that the presented method can be used for all loading conditions and apply to different boundary conditions. Finally, the method is experimentally validated by the simply supported beam specimen made of steel subjected to impulsive loads, and cracked concrete beam subjected to static loading. In order to evaluate the accuracy of the estimated distributed rotation angles, the global index of vertical displacement calculated by the estimated distributed rotation angles is compared with the directly recorded data by displacement meters. Experimental results show that the method can obtain distributed rotation angles with high precision, and it will cause large relative error if material nonlinearity of cracked concrete beams is neglected.