Fluid impact forces on a bridge superstructure in the horizontal and vertical directions due to tsunami inundation, represented by a solitary wave, were investigated through a large-scale laboratory experiment and numerical simulations. The experiment was conducted in a two-dimensional large wave flume using a 1:5 scale steel girder and concrete slab bridge model, tested under shallow water waves at two water depths. Wave forces measured in the experiment were used to validate and assess the numerical predictive capability of a nonlinear hydrodynamic model. A numerical parametric study was conducted to determine the effect of variations in bridge elevation and wave height on the magnitude of the horizontal and vertical forces and overturning moment. Finally, an improved simplified design procedure based on the experimental and numerical results is proposed.

In view of the widespread damage to coastal bridges during recent tsunamis (2004 Indian Ocean and 2011 in Japan) large-scale hydrodynamic experiments of tsunami wave impact on a bridge with open girders were conducted in the Large Wave Flume at Oregon State University. The main objective was to decipher the tsunami overtopping process and associated demand on the bridge and its structural components. As described in this paper, a comprehensive analysis of the experimental data revealed that: (a) tsunami bores introduce significant slamming forces, both horizontal (Fh) and uplift (Fv), during impact on the offshore girder and overhang; these can govern the uplift demand in connections; (b) maxFh and maxFv do not always occur at the same time and contrary to recommended practice the simultaneous application of maxFh and maxFv at the center of gravity of the deck does not yield conservative estimates of the uplift demand in individual connections; (c) the offshore connections have to withstand the largest percentage of the total induced deck uplift among all connections; this can reach 91% and 124% of maxFv for bearings and columns respectively, a finding that could explain the damage sustained by these connections and one that has not been recognized to date; (e) the generation of a significant overturning moment (OTM) at the initial impact when the slamming forces are maximized, which is the main reason for the increased uplift in the offshore connections; and (f) neither maxFv nor maxOTM coincide always with the maximum demand in each connection, suggesting the need to consider multiple combinations of forces with corresponding moments or with corresponding locations of application in order to identify the governing scenario for each structural component. In addition the paper presents “tsunami demand diagrams”, which are 2D envelopes of (Fh, Fv) and (OTM, Fv) and 3D envelopes of (Fh, Fv, OTM), as visual representations of the complex variation of the tsunami loading. Furthermore, the paper reveals the existence of a complex bridge inundation mechanism that consists of three uplift phases and one downward phase, with each phase maximizing the demand in different structural components. It then develops a new physics-based methodology consisting of three load cases, which can be used by practicing engineers for the tsunami design of bridge connections, steel bearings and columns. The findings in this paper suggest the need for a paradigm shift in the assessment of tsunami risk to coastal bridges to include not just the estimation of total tsunami load on a bridge but also the distribution of this load to individual structural components that are necessary for the survival of the bridge.

The present work describes the implementation of an advanced solitary wave generation system in the mesh-less SPH-based DualSPHysics model to simulate tsunami-like solitary waves. Three different generation theories have been implemented and are extended to generate multiple solitary waves. The numerical model is validated against theoretical solutions and physical model results from three different experimental campaigns, which investigated respectively: i) the forces exerted on harbour protections; ii) the run-up of solitary waves on a gentle beach; and iii) the impact of double solitary waves on two cylindrical reservoirs. The differences of modelling breaking and non-breaking wave conditions are highlighted. The results demonstrate the capability of DualSPHysics to represents the main hydrodynamic properties of solitary waves when interacting with the shoreline or with coastal structures. The applicability of DualSPHysics to coastal engineering problems is enhanced, being the model already capable of generating monochromatic waves and random sea states.

A broadly accepted paradigm is that vegetation reduces coastal dune erosion. However, we show that during an extreme storm event, vegetation surprisingly accelerates erosion. In 104-m-long beach-dune profile experiments conducted within a flume, we discovered that while vegetation initially creates a physical barrier to wave energy, it also (i) decreases wave run-up, which creates discontinuities in erosion and accretion patterns across the dune slope, (ii) increases water penetration into the sediment bed, which induces its fluidization and destabilization, and (iii) reflects wave energy, accelerating scarp formation. Once a discontinuous scarp forms, the erosion accelerates further. These findings fundamentally alter the current understanding of how natural and vegetated features may provide protection during extreme events.