Hydro-structural investigation of storm surge impact on coastal bridge pier by smoothed particle hydrodynamics

Abstract

Extreme waves, i.e., tsunamis and storm surges, can generate tremendous hydraulic bores capable of inflicting considerable damage to near-shore bridge infrastructure, often leading to structural failure. However, accurate prediction of these dynamic loads is quite challenging; in fact, there is an incontestable lack of established methods to quantify these extraordinary phenomena. Therefore, advanced research is required in this field to understand, analyze and predict structural response to extreme wave loadings. The conventional numerical approach to studying hydrodynamic impact is based on Eulerian grid-based, e.g., finite volume or diffused element algorithms. These perform well with perfectly defined simulation domains. However, in case of severe surface deformation, these grids must be continually reconstructed, which is time-intensive and introduces cumulative system errors. As Smoothed Particle Hydrodynamic (SPH) integrates the hydrodynamic equations of motion on each particle in Lagrangian formalism, it can handle complex wave non-linearity without mesh constraints. Therefore, this thesis explicitly relies on SPH to study the mechanics of violent surge-structure interaction. The SPH model is validated against past experimental studies on surge bore impingement upon vertical structures. Then the validated model domain was extended to study bridge pier-system response to cyclone-induced tidal surges, access its hydrodynamic characteristics and impact on structural design parameters. The first part of the thesis studies the hydrodynamic forces acting on elevated pilecap systems (i.e., grid, hexagonal) under different surge intensities. At impact, the gridded pile layout was found to offer greater resistance to incident surge, having a velocity reduction rate of 14.00-23.52% verses hexagonal system’s 8.22-19.76%. The hexagonal pilecap's flow splitting action helps to reduce average horizontal stress by 27.96% at impulsive contact and 7.4% under quasi-steady flow. In addition, the study proposes rationalized force diagrams to be applied in design near-shore elevated structures. The second part of the study investigates impulsive wave-load and post-impact kinematics of complex pier geometries subjected to a solitary storm surge bore. The research found the hexagonal cross-section to be the optimal pier geometry, which at a time imparts minimum resistance to the incident surge field and is capable of reducing the maximum hydrodynamic thrust by 52%. Lastly, the present study investigates the influence of in-situ water depth on surge response amplification in a protected estuarian bridge site. In-situ water was found to act as a catalyst to amplify surge intensity. Two successive impulsive shocks were recorded to hit the central and side-piers. The first shock is governed by pseudo-static water depth, wave incidence angle, and impact velocity, while the second relies on surge fluid mass, lateral bed slope, and revetment height. The side-piers were also found to be susceptible to lateral hydrodynamic thrust reaching up to 21.10% (full-tide scenario) of the maximum inline force. The result of the study is expected to contribute to formulating new guidelines for resilient hydraulic design of coastal and deep-water bridges.