Numerical Study of the Coastal Bridge under Surge Waves during Extreme Hurricane

In the past decades, extreme hurricanes have caused huge damage to coastal highway bridges in the United States and resulted in a great financial loss to society. In order to minimize the associated damage and improve the behavior of costal bridge during the extreme hurricane, this dissertation investigates the nonlinear interaction between water waves and superstructure of coastal bridge by numerical method. This study proposes a new fluid structure-interaction (FSI) model, which combines the features of ANSYS Mechanical package and Fluent. The major advantage of the proposed model is more flexibility in adjusting boundary conditions of the bridge superstructure. Current study focuses on performing full-scale numerical investigation of prototype bridge (I-10 Bridge over Escambia Bay) when subject to solitary waves.;This dissertation comprises three broad themes. The first one is to identify the critical connection between bridge superstructure and substructure. By assuming deck is implemented with strong anchorage at each girder and cannot move vertically, the general characteristic of connection forces acting on level bridge deck is revealed for typical wave conditions. Parametric study is then performed to discuss the effect of bridge properties such as horizontal flexibility of bridge deck and deck inclination angle. The reliability of linear distribution model in evaluating critical connection force is examined for both level and inclined bridge deck. The second one is to investigate the characteristic of resultant forces of deck at the bent level. With a deeper understanding of wave forces imposed on vertically fixed bridge deck, the effect of vertical flexibility on resultant forces is discussed by assuming deck can rotate about onshore side once wave load overcome the deck weight. The relationship between axial force component and overturning moment component is firstly displayed by introducing the concept of interaction diagram. Afterwards, a simpler empirical model that can capture major characteristics of connection forces on vertically fixed deck is proposed and tested. Finally, the third one addresses the issue that if it is possible to improve behavior of coastal bridge when subject to wave loads by adjusting connection properties. Four connection properties that may affect structural flexibility and four performance characteristics that are used to reflect deck behavior are selected. Grey-based Taguchi method is then adopted to find best combination of connection property, which is a multi-objective, multi-factor optimization problem. After finding the optimal setting, the significance of each structure parameters is evaluated based on ANOVA analysis. Based on results from Grey-based Taguchi method, it is concluded that the best way to improve the behavior of the bridge deck is increasing the stiffness and strength of the connection. However, with the concern that the strong connection would inevitably increase transferred wave loads and may arise localized concrete cracking problem, nonlinear SOLID element that has cracking features is adopted to model RC bridge deck. Weak region on bridge deck is identified by observing cracking pattern caused by wave loads. The efficiency of increasing reinforcement and adjusting the location to apply constraint in relieving concrete cracking problem is discussed.