Measurement Model for the Maximum Strain in Beam Structures Using Multiplexed Fiber Bragg Grating Sensors

This study develops a strain measurement model for beam structures subjected to multiloading conditions by defining the strain-shape function and participation factors to overcome the limitations of strain measurements using fiber Bragg grating (FBG) strain sensors. Using the proposed model, the maximum strain in a beam is obtained by the sum of the strains caused by the different loadings acting separately. In this paper, the strain-shape functions for various loading and support conditions are provided, and a system of equations is defined to calculate the participation factors. Furthermore, the influence ratio is defined to identify the influence of each loading on the value of the total strain. The measurement model is applied to the monitoring of the maximum strain in a 4 m long steel beam subjected to two concentrated loads. For measurements during the test, seven FBG sensors and nine electric strain gauges (ESGs) were attached on the surface of the bottom flange. The experimental results indicate a good agreement between the estimated strains based on the model and the measured strains from ESGs. Furthermore, the dependency of the locations for the FBG sensors installed at the beam structure on the selection can be avoided using the measurement model.