レール支持部に存在する力学的非線形性が,レールの共振周波数と軸力との関係に及ぼす影響について考察した.そのために,まくらぎ位置を節とするレールの共振モードを対象に,調和加振下での定常解を与える汎関数をLagrangianの時間平均より求めた.当該汎関数より定常解や共振条件を導出し,共振周波数-軸力関係の加振力に対する鋭敏性を議論した.また,レール加振を模擬した数値解析を通し,本理論の妥当性を検証した.The influence of mechanical nonlinearity in rail supports on the resonant frequency-rail axial load relationship is investigated. To achieve this, a harmonic load exciting the pinned-pinned resonance mode is considered, and a functional which derives a steady-state solution is formulated by time average of the Lagrangian. In the theoretical study, the nonlinearity is introduced in the rotational stiffness at each sleeper support. Based on the variations of the functional, the sensitivity of the above relationship to the load amplitude is revealed. Furthermore, through numerical analyses, validity of the theory is proved.