Investigation on the application of periodic structural materials having band gap characteristics to railway vehicle floor panel supports

Periodic structures are known to have specific frequency ranges, called band gaps, in which the propagation of elastic waves is suppressed. Unlike conventional methods that require individual countermeasures for each vibration mode, vibration suppression using band gaps can effectively reduce elastic vibrations and structure-borne noise within specific frequency ranges. In this study, a new floor structure for railway vehicles is proposed, where the floor panel is supported by periodic composite beams with band gap characteristics, aiming to reduce vibrations transmitted from the underfloor (which may induce structure borne noise). The periodic composite beam consists of unit cells composed of two elements with different structural properties. Numerical calculations based on the energy method were carried out to derive the dispersion curves and to perform frequency response analysis, confirming the formation of band gaps and the absence of resonance peaks within these frequency ranges. Furthermore, power spectral density (PSD) analyses were conducted under random excitations applied at both beam ends to simulate actual vibration inputs from the underfloor of railway vehicles. The results showed no PSD peaks within the band gap frequency range at the floor support points, demonstrating the potential of the proposed structure to reduce vibration transmission to the floor panel.