The RTRI proposed a technique to improve the bending rigidity and strength of carbodies by making the best use of the inner frames, which were previously not recognized as main members that bear carbody strength.

Reinforcing components were attached at the ceiling, door pockets, and floor of the rigidity test car (Fig.1), which was designed and fabricated to represent a commuter-type car, and the components formed the ring structures inside the carbody. Static load tests using the rigidity test car were performed and the equivalent bending rigidity of the carbody with the ring structure was increased by approximately 13% compared with that of the carbody alone.

In addition, it was also verified that the ring structures had an effect to restrain the independent out-of-plane deformation of each panel of the carbody (which is one of the features of the carbodies made of stainless steel), and that the natural frequencies corresponding to the main vibration modes increased by approximately 3 to 6 Hz (Fig.2). As a consequence, it is expected to be easier to investigate measures for reducing carbody bending vibration, because the carbody deforms in a beam-like manner. Furthermore, along with the rise in the natural frequencies, human sensitivity to the vertical vibration is lowered, which is advantageous in terms of the ride comfort.

The RTRI also performed quasi-static strength tests for full-scale partial carbodies (2m wide) against the load from the body side (Fig.3) and the result showed that the “ring structure” specimen reduce the amount of diagonal deformation up to 40% approximately comparing with the normal specimen. Accordingly, the ring structure provides the possibility for reducing the carbody deformation when a railway vehicle overturns in accidents.