STRAIN MEASUREMENT ON PBL SHEAR CONNECTOR GROUP BASED ON PPP-BOTDA DISTRIBUTED FIBER OPTIC SENSING TECHNIQUES

In order to investigate the shear transfer mechanism among shear connectors of PBL groups, fiber optic sensing techniques are introduced into the strain measurement of perforated plates on the interface friction effect. Measurement principles of pulse-preppump Brillouin optical time domain analysis (PPP-BOTDA) techniques are presented, then a strain transfer model for matrix-fiber structures is built according to the shear lag theory of multiple middle-layers and strain transfer formulas for the surface-attached fibers are deduced. Based on the static loading tests of four four-row PBL shear connector group specimens, spatially distributed strain measurement for the perforated plate and surrounding concrete is achieved, and parameter sensitivity analysis on the strain transfer of distributed fiber optic sensors is conducted. The measurement results and analysis show that the pasted width and the coat thickness of optical fibers have significant effect on the strain transfer ratio, but the shear modulus of the adhesive layer has no obvious effect on the strain transfer in case of invariant spatial resolution of the instrument. Comparing the strain data from strain gauges and optical fibers, it is evident that both types of optical fibers have preferable measurement accuracy, and the test results are consistent with the sensitivity analysis in theory. The measurement method for distributed fiber optic sensors on the basis of PPP-BOTDA techniques solves the problems of traditional strain measurement using resistance strain gauges, and can be used for distributed large-strain and high-accuracy measuring for bridge structures by means of the setup method of the optical fibers.