Tsunami Forces on Selected California Coastal Bridges.

摘要

Tsunami horizontal and vertical forces and overturning moment time histories are computed for selected California coastal bridges. For each tsunami flow condition, the horizontal and vertical forces and overturning moment time histories are computed for four selected time periods containing: a) initial impact, b) occurrence of the maximum tsunami water velocity, c) occurrence of maximum tsunami momentum flux, and d) occurrence of maximum tsunami mass flux. It is found that the initial stage of tsunami loading on a bridge superstructure is a combination of horizontal and uplift forces. Maximum uplift force during the initial impact time period is found to occur when the tsunami water free-surface elevation reaches the top of the bridge barrier right before overtopping the bridge and starting to flow onto the bridge deck. It is observed that the time period representing the initial impact of the tsunami on the bridge superstructure leads to maximum horizontal force, downward vertical force, and overturning moment. Overall maximum uplift force is found to be in tsunami scenarios where the bridge superstructure is already inundated. The maximum horizontal force, downward vertical force, and overturning moment do not change significantly for different water elevations. Maximum uplift force is observed to increase for higher tsunami water free-surface elevations where the corresponding flow velocity is higher. Analyzing a deck-girder bridge considering the failure of the first seaward girder shows a 15% reduction in maximum horizontal force. Uplift force is found to be approximately 25% larger for the bridge with a failed first girder. A set of equations are proposed to compute maximum horizontal and vertical forces on bridge superstructures based on a regression analysis of the simulation results. Comparison between numerical results from simulations and the estimated forces using the recommended approach shows a good agreement between numerical predictions and formula estimations of the tsunami forces.