The 2011 Great East Japan Tsunami has altered our traditional concepts for estimating loadings on structures. Prior to this event, we generally understood that reinforced concrete structures -those often used for critical coastal facilities -could withstand tsunami actions. This is no longer the case. Many concrete buildings and coastal protective structures (seawalls, coastal dykes and the like) failed due to the 2011 Tsunami. In this paper, the existing design guidelines are reviewed. We point out that some of the force-estimation methods recommended in the guidelines are rational, while others are not. Then we introduce a methodology to evaluate building's global stability emphasizing the effect of buoyant force. Buoyancy reduces the net structural body force; thereby reducing the restoring forces to resist sliding and overturning failures. Buoyancy force is an upward pressure force under the building, which is caused by an increase of pore-water pressure in the soil by excess water weight on the ground surface; therefore it takes a finite time to build up. We demonstrate that the effect of buoyancy force depends on 1) duration and depth of tsunami inundation, and 2) burial depth of the building. We also note that if and when a building interior is flooded (due to breakaway walls or windows), the flooded water increases the effective body force (weight); hence producing a stabilizing effect. Example calculations are given to demonstrate the importance of the delayed action of buoyancy force and breakaway walls and windows.

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Experim ental and Analytical Study of W ater-D riven Debris Im pact Forces on Structures1Water-driven debris generated during tsunamis and hurricanes can impose substantial impact forces on structures that are often not designed for such loads. This paper presents the design and results of an experimental and analytical program to quantify these potential impact forces. Two types of prototypical debris are considered: a wood log and a shipping container. Full-scale impact tests at Lehigh University (LU) were car ried out with a wooden utility pole and a shipping container. The tests were carried out in-air. The purpose of these tests was to provide baseline, full-scale results. Because of size limitations, a 1:5 scale shipping container model was used for in-water tests in the Oregon State University (OSU) large wave flume. These tests were used to quantify the effect o f the fluid on the impact forces. Results from both experimental programs are pre sented and compared with analytical predictions. The predictions are found to be in suffi cient agreement such that they can be used for design. A fundamental finding is that the impact forces are dominated by the structural impact, with a secondary effect provided by the fluid. Both forces are quantified in the paper.

Water-driven debris generated during tsunamis and hurricanes can impose substantial impact forces on structures that are often not designed for such loads. This paper presents the design and results of an experimental and theoretical program to quantify these potential impact forces. Two types of prototypical debris are considered: a wood log and a shipping container. Full-scale impact tests at Lehigh University were carried out with a wooden utility pole and a shipping container. The tests were carried out in-air, and were designed to provide baseline, full-scale results. A 1:5 scale shipping container model was used for in-water tests in the Oregon State University large wave flume. These tests were used to quantify the effect of the fluid on the impact forces. Results from both experimental programs are presented and compared with theoretical predictions. The analytical predictions are found to be in sufficient agreement such that they can be used for design. A fundamental takeaway is that the impact forces are dominated by the structural impact, with a secondary affect provided by the fluid. Both forces are quantified in the paper.

No abstract