Analysis of Required Separation Distances of High-Pier Bridges Subjected to Non-stationary Ground Motions

To investigate the influence of non-stationary ground motions on required separation distances, the influence of site conditions on non-stationary gap under different intensities was analysed based on the random vibration theory and pseudo excitation method. First, the mathematical formulation clarifying the relationship between the required relative displacement and earthquake intensity was derived. Second, the minimum gap required between two adjacent girds to prevent seismic pounding was determined from the maximum relative displacement based on theoretical analysis. Finally, a real continuous rigid bridge was used to obtain the required gap length spectrum between two adjacent decks for considering non-stationary seismic excitations with different intensities under different local site conditions. Furthermore, the influence of actual site conditions and uniform site conditions on the required separation distance was investigated. Numerical results reveal that actual site conditions have the most obvious effect on the time-dependent mean square deviation of relative peak displacement, which is four times the corresponding value for firm site conditions. The mean values of the required separation distance for different intensities are larger than the corresponding values for uniform site conditions by 36%, 69%, and 73% for soft sites, median sites, and firm sites, respectively, whereas the mean square deviation is 45%, 74%, and 78%, respectively. The required separation distance under stationary seismic excitations is 20%–30% larger than that under non-stationary seismic excitations.