This data set contains distributed fiber optic strain data and Python scripts for evaluation. The data was collected 2022-10-04 during experiments on a decommissioned bridge girder of type BTE 311.080.12. These prefabricated and post-tensioned girders were produced in the former GDR. In the experiments, tendons were deliberately damaged by cutting wires. Two locations on opposite lateral sites of the girder 1 m from the girder's middle were selected: C1 and C2. The data shows strain changes measured with a distributed fiber optic sensor (DFOS) installed in the underside of the girder. The DFOS was routed in three segments along the free span of the girder.