This repository publishes the data and Matlab app for the paper titled, "A Mechanical Model to Interpret Distributed Fiber Optic Strain Measurement at Displacement Discontinuities" published in Structural Health Monitoring. Distributed fiber optic (strain) sensing (DFOS), which provides the unique advantage of sensing damage (e.g. cracking) at locations that are not known a priori, has been increasingly used in civil engineering. Quantitative crack measurement requires the translation of a discontinuous displacement field at the crack to a continuous strain deformation in the fiber. The mechanical model contributes to the explanation of Distributed Fiber Optic (strain) Sensing (DFOS) results on concrete sensing. The crack sensing results with DFOS of one RC specimen under tension and the corresponding visualization app are also included in this repository.