Actuality of Structural Health Monitoring (SHM) of transport vehicles grows up last years in energy and transport sectors caused by safety and economic reasons. The SHM of operating structures meets problems that described briefly in the introduction below. Piezo film sensors application instead of accelerometers for diagnostic systems may move SHM ahead but needs solutions of theoretical, economical and practical justification. To find theoretical relation between vibrations and deformations and to validate it experimentally is the main purpose of this work. The paper considers theoretical approach to relation between structural vibrations and deformations assuming a pure bending of the structure. Relationship between displacements and deformations is discussed based on the known equations of Strength of Materials theory. The expressions describing this relationship regarding to the oscillating beam in dynamic and static state are provided by some restrictions. Experimental validation of the theoretical results was conducted applying the modal estimation techniques and its results are discussed. Experimental Modal Analysis (EMA) techniques provide Frequency Response Function (FRF) using signals of accelerometers and Operational Modal Analysis (OMA) allows determination of normalized deformations supplied by piezo film sensors. Comparative analysis in view of theoretically stated relationship shows good convergence between experimentally measured FRF and deformations subject to theoretical amendment. Evidences of benefits of piezo film sensors application for modal testing and SHM are given and detailed in the article. In conclusions the main advantages of piezo film sensors application are noted and acknowledgements presented.