Accurate rotation identification of flexural structures using long-gauge fiber optical sensors.

This article focuses on the identification of rotational behavior in reinforced concrete (RC) beams and columns using long-gauge fiber Bragg grating (FBG) optical sensor arrays for structural health monitoring (SHM). It compares four rotation identification methods based on two mechanisms: the plane section assumption (Mechanism A) and the sectional fiber model (SFM)-based neutral axis identification (Mechanism B), using strain measurements from concrete surfaces and steel reinforcements. Experimental results from laboratory tests on RC beams and columns show that Mechanism A is effective under small (elastic) deformations but loses accuracy after concrete cracking, while Mechanism B maintains accuracy through cracking and large (inelastic) deformations, especially when using sensors on steel reinforcements. Field case studies on bridge grids and columns further validate the applicability of long-gauge FBG sensors for dynamic rotation identification, supporting their use in monitoring structural performance and stability in both elastic and large deformation states.