Long-gauge fiber sensors have been widely used in silos, bridges and high-rise buildings for the detection of damages or excessive deflection in the past several years. This paper explores their potential for comprehensively monitoring reinforced concrete (RC) beams under the complex interplay of shear and flexure. Leveraging the distributed sensing capabilities of long-gauge optic sensors, it measures both deflection and shear deformation across the entire beam length. Additionally, a decoupling method was introduced to unravel the individual contributions of shear and flexure to the overall deformation, providing valuable insights into the beam's behaviours. The experimental results show that the estimated deflection and shear deformation of RC beams obtained from long-gauge optic sensors fit well with that from LVDTs.