Tsunami force estimation on inland bridges considering complete pier-deck configurations

Abstract

Theoretical approach for estimating tsunami-induced forces with today’s state-of-the-art cannot be easily applied for bridges due to the complexities of the wave propagation on shore and wave-structure interaction. In this thesis, the research works focus on the investigation of the flow characteristics of tsunami surges around inland bridges and tsunami pressures and forces on bridges. Stand-alone piers and complete pier-deck bridge models which are proportionally scaled from a typical I-girder bridge prototype were employed experimentally. Five configurations of bridge decks with and without perforations in girders and/or parapets were considered. The experimental results reveal that the surge forces on the piers measured from a complete pier-deck model are substantially higher than those measured from the stand-alone piers model, which indicates that the customary method of computing the surge forces on the pier independently for simplicity under the current practice needs to be reviewed for the case of the tsunami-pier-deck interaction. In addition, bridges with perforation in the girders and/or parapets, which have not yet been studied in research for tsunami hazard mitigation, show reduction of forces and less energy input into the structure throughout the time-history. A numerical model in accordance with the physical model was next constructed in a computational fluid dynamics (CFD) program and verified using the recorded experimental data. The validated model was then extended to simulate bridge prototypes of seven different deck clearances subjected to the most severe wave scenario. The issue of simplification in bridge deck is addressed. The utilization of a complete pier-deck bridge model for a realistic representation is supported by the numerical results. With the piers excluded or simplification of an I-girder deck to a box girder deck, the maximum horizontal and vertical uplift forces on the deck at the initial wave impingement are significantly underestimated by about 15% and 60% from those predicted for the actual configuration, respectively. Finally, an empirical method to estimate tsunami forces on bridge decks was proposed. Tsunami forces on bridge decks are categorized into four main components, i.e. horizontal peak, horizontal slowly-varying, vertical uplift and additional gravity forces. Pressure distribution of the horizontal slowly-varying force on bridge deck is established and three other force components are computed as some multiple of the mean slowly-varying force component.