Abstract: To investigate the safety performance of post-tensioned prestressed segmental columns subjected to stochastic earthquake excitations, a novel nonlinear modal updating approach is proposed for structural dynamic reliability assessment. An improved unscented Kalman filter (UKF) approach is firstly developed to calibrate nonlinear modal parameters based on the measured structural responses under seismic loads, and the optimized modal parameters can be obtained by performing multiple UKF iterations. Then, the updated nonlinear model is applied for dynamic reliability assessment of the post-tensioned prestressed segmental columns under input uncertainties, and the effects of the intensity of the applied earthquake loads are further considered. Numerical simulations on a post-tensioned prestressed segment column structure subjected to seismic loads are conducted to validate the feasibility and accuracy of the method proposed. Furthermore, a scaled shake table structure of post-tensioned segmental columns subjected to bi-directional earthquake exactions is applied to verify the effectiveness of the approach proposed. Both numerical and experimental results have shown that the strategy proposed is accurate and effective for nonlinear modal updating of segmental columns, and the results updated are capable for reliability assessment of such type of structures under input uncertainties.