United States Department of Transportation
i
Tsunami Loads on Straight and Skewed Bridges – Part 2: Numerical Investigation and Design Recommendations
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2021-03-01
[PDF-9.32 MB]
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Edition:Final Report
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Abstract:Despite the documented vulnerability of coastal bridges in recent tsunami events, no formal guidance exists to date for the tsunami design of such structures. To contribute to the development of such guidelines, this report presents the results of a numerical investigation into tsunami-induced loads on bridges. Following extensive validation of an incompressible hydrodynamic solver, three existing bridges owned by the Oregon Department of Transportation, are investigated, including open-girder and box-girder superstructures. These analyses revealed that when a bore impacts a straight bridge, large impulsive horizontal (Fx) and uplift (Fy) loads together with an overturning moment about the longitudinal axis of the bridge (Mz) are simultaneously applied to the bridge, increasing the likelihood for severe damage. As the angle of skew increases the magnitude of the impulsive component of these loads decreases, leading to a decreasing trend in Fx, Fy and Mz. On the other hand these structures are also subject to (i) a force normal to the direction of wave propagation, and (ii) moments about the y- and z-axes. The Fz force and the yaw moment My can have a detrimental effect on bridge performance because they generate out-of-plane horizontal loads that can result in unseating of the deck, while the roll moment Mx can overload the structural components (bearings and shear keys) at one end of a skewed deck. Another important finding is that while a tsunami wave that strikes a straight bridge at an oblique angle generates significant three-dimensional effects similar to skewed bridges, such a wave can lead to more severe deck loads due to the interaction of the wave with the bridge abutments and a subsequent channeling effect. Finally, to assist bridge designers, the report presents a simplified methodology for the tsunami design of skewed bridges, and performance criteria for bridges in tsunami-prone areas, based on (i) two tsunami levels, (ii) three bridge operation categories, and (iii) three performance levels to quantify the criteria.
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