Doctor of Philosophy (Ph.D.)
Degree Granting Department
Civil and Environmental Engineering
Manjriker Gunaratne, Ph.D.
Rajan Sen, Ph.D.
Mark Ross, Ph.D.
Autar Kaw, Ph.D.
Kandethody Ramachandran, Ph.D.
Dual hazards, Incremental dynamic analysis, Nonlinear time history, Scour depth, Ship impact, Soil structure interaction, Fragility curves
Scour has been the number one cause of bridge failure in the United States with an average of 22 bridges collapsing or being closed owing to severe deformation each year . This work attempts to deal with two important issues: (1) Potential bridge failures during the co-occurrence of scour and ship impact; (2) Incorporating IDA analysis to predict bridge responses based on barge and collision parameters, and to generate fragility curves to predict the probability of exceedance damage states.
For bridges, flooding is considered the most threatening hazard. According to the National Bridge Inventory (NBI) , 500,000 out of 615,000 bridges that cross waterways are exposed to floods, and 26,000 bridges in the U.S. are deemed scour critical (the bridge foundation is not stable). Bridge substructure component design is based on 100-year and 500-year floods.
Scour is not force effect, but scour is the loss of foundation lateral support. This loss of support affects the stability of the foundation and has significant change on forces acting on the bridge structure. The American Association of State Highway Transportation officials (AASHTO) specification , Load Resistance Factor Design (LRFD) methodology, does not combine probability of two extreme events: vessel collision and the bridge scour. AASHTO believes the probability of those events is very low; therefore, those events are determined separately.
The two most common causes of bridge failure are hydraulic failure due to scour of the bridge foundation and collision of vessels. Scour, the loss of soil caused by high-velocity flowing water, adversely affects the stiffness of bridges. Scour has been the predominant cause of bridge failures in the U.S., accounting for 60% of them, and it may also result in excessive rotation of the column and displacement of the deck. The second most common cause of bridge failure in the U.S. is vessel collision, responsible for 12% of them. The above hazards are typically treated independently as single extreme events according to the AASHTO design guidelines. However, vessel collision with scoured bridge piers and piles can co-occur, and there is a lack of assessment methodologies to address this synchronous dual-hazard scenario. Based on past statistics, narrow and congested waterways are more prone to collisions between ships and bridges. The U.S. and the world are projected to experience an increase in ship sizes and higher frequencies of large vessel navigation in waterways due to global economic growth. Therefore, ship impact scenarios need closer scrutiny in the future. The aim of this research is to highlight and investigate potential bridge failures during the co-occurrence of scour and ship impact. The results of this research will help engineers to address such risks. The results illustrate that depending on the surrounding soil properties, ship impact locations, nonlinear dynamic load time history, and scour depth conditions, shear demand of the column base decreases due to increased scour at lower impact locations with clay soil configuration. In addition, the moment demand on the bridge column increases with the scour depth. The results of the parametric studies show larger displacement in piles under increased scour and ship impact locations close to pile cap, especially for clayey soil foundations.
In addition to analyzing aforementioned multi-hazardous events, this dissertation examined Incremental Dynamic Analysis (IDA) , a method of parametric analysis used in nonlinear dynamic systems for estimating the seismic capacities of bridges. IDA is usually applied to estimate the performance of structures under extreme events. In this research, IDA was used for evaluating the capacities of bridge components under the dual hazards of vessel collision and scour. In order to predict bridge response, a finite element model of the bridge was developed in OpenSees (Open system for earthquake engineering simulation) software , and IDA analysis was performed to establish the response parameters. The selected bridge configuration was subjected to a direct barge inertia mass force with an initial velocity and a force-deformation stiffness spring to assess the effect of the above hazards on the responses of bridge components such as displacement, rotation, shear, and moment. The IDA plot typically illustrates the intensity measure (IM) on the vertical axis and the damage measure (DM) on the horizontal axis. This study focuses on the barge velocity as the intensity measure using increments of 0.25 m/sec varying from 0 to 2 m/sec with a constant barge mass of 1000 tons while the responses of the above bridge components express the damage measure. In all test cases, three different ship impact points (3, 4, and 5 m) and five different scour levels (0 m, 1 m, 2 m, 3 m, and 4 m) are used. The results show that at higher vessel velocities, the damage responses of the bridge increase as scour levels increase. It is also shown that using this type of an IDA parametric study, engineers would be able to make accurate predictions of bridge responses due to vessel collision under scour conditions and estimate the performance of structures under the above dual hazards. Hence, the IDA can be considered an additional tool of performance assessment under the above conditions. Furthermore, using the IDA results, the damageability of the bridge column under the intensity measure of barge velocity was evaluated through fragility analyses. The results show that the scour depth leads to an increase in the probability of exceedance of all damage levels thus contributing to large deformations in the bridge column under barge impact.
Scholar Commons Citation
Irhayyim, Amir S., "Assessment of Scoured Bridges Subjected to Vessel Impact Using Nonlinear Dynamic Analysis" (2022). USF Tampa Graduate Theses and Dissertations.