United States Department of Transportation
i
Tsunami Loads on Straight and Skewed Bridges – Part 1: Experimental Investigation and Design Recommendations
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2021-02-01
[PDF-19.98 MB]
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Edition:Final Report
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Abstract:This report presents the results of a large-scale experimental investigation of tsunami impact on straight and skewed bridges. The 1:5 scale specimens had realistic structural components and dynamic properties, and were subjected to a range of simplified unbroken solitary waves and more realistic bores. The unique experimental data revealed: (a) the complexity of the tsunami inundation mechanism of bridges and the overloading of the offshore bearings and columns, due to the large overturning moment (OTM) generated by the wave slamming the offshore girder and overhang, (b) the significant difference between the effects introduced by simplified unbroken solitary waves and more realistic bores, (c) the major role of structural dynamics and fluid-structure interaction for the estimation of design forces, and the possibility of dynamic amplification when the bridge is impacted by a bore, (d) the increase of both the total uplift forces and the OTM in bridges with diaphragms due to the air-entrapment, (e) the dependence of the tsunami loads on the bridge type, with box-girder bridges witnessing on average uplift forces 134% higher than those in I-girder bridges, (f) the modification of the hydrodynamic flow caused by solid rails, which increases both the horizontal and downward tsunami loads, and (g) the promising use of air-vents in the deck as a mitigation strategy against tsunamis, in which both the number and the location of the venting holes are optimized in order to maximize the air release. Based on the above findings, the authors developed two simplified methods that can be used for the tsunami design of bearings and other structural components necessary for the survival of straight bridges. While the above findings are applicable to straight bridges, skewed ones witness more complex loads, including significant roll and yaw moments, which should be considered in their design. These moments lead to non-uniform distribution of the tsunami loads to the two supports of the deck and the individual bearings with (i) one abutment having to sustain up to 96% of the total horizontal force, and the other one up to 146% of the total uplift, and (ii) the bearings of the offshore obtuse corner attracting 95% of the total deck uplift.
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