This award is an outcome of the NSF 09-524 program solicitation "George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) Research (NEESR)" competition and includes the University of Hawaii (UH, lead institution), Lehigh University (LU, subaward), and Oregon State University (OSU, subaward). This project will utilize the NEES equipment sites at Lehigh University and Oregon State University.
The objective of this research project is to improve our understanding of, and predictive capabilities for, tsunami-driven debris impact forces on structures. Of special interest are shipping containers, which are virtually everywhere and which will float even when fully loaded. The forces from such debris hitting structures, for example evacuation shelters and critical port facilites such as fuel storage tanks, are currently not known. We will carry out experiments at NEES@OSU and NEES@Lehigh to improve our understanding of low speed impact of heavy debris and to develop and validate two numerical models: a simplified model that can be used for design, and a more complex fluid-structure interaction model based on computational fluid dynamics. This simulation-based model will allow us to explore complex parameters not included in the simple model and to consider scenarios not covered by experiments.
For the experiments at the NEES@Lehigh facility, we will quantify experimentally the nonlinear behavior of full scale shipping containers as they slam into structural elements "in air". These results will be used to calibrate our computational models. The experimental and model results will be used to design a simpler, 1:5 scale model that mimics container behavior for a second series of tests at the NEES@OSU Tsunami Research Facility. In these tests, tsunami "waves" will drive the model debris against a test structure. These tests will provide actual data from water-driven debris, which will be used to validate numerical models developed at UH. The OSU tests will also shed light on the amplification that may result from the surrounding fluid mass. Similar tests will be conducted for "woody" debris, such as logs and telephone poles.
Intellectual Merit: A key goal for earthquake and tsunami engineering is "community resilience", that is, the ability of a community to withstand an event without catastrophic damage. A significant threat to structures in the tsunami inundation zone is impact from debris driven by the tsunami flow; characterization of these forces is especially important to life-safety related to vertical tsunami evacuation shelters. Building code provisions are not well-developed to handle typical tsunami-driven debris, such as logs, telephone poles, and steel shipping containers. Recent work on impact of flexible debris has shown that the wave propagation in the debris governs the forces applied to the impacted structure and that force amplification that may occur as a result of the surrounding fluid depends on the wave propagation in the two media. This project will obtain a rich set of experimental data to reveal the behavior of low speed, heavy debris impact on structures. In addition, numerical models will be created to enhance our simulation capability of debris impact forces.
Broader Impacts: The results of this study will contribute to improving community resilience to tsunamis. The results have the potential to impact significantly the specification of design forces for debris impact, which is an especially important design consideration for tsunami shelters, fuel and chemical storage tanks, and port and industrial facilities, all of which may unavoidably be located in tsunami inundation zones. In addition, the results will be applicable to hurricane-driven, water-borne debris, and to some extent to barge and ship collisions of bridge piers, docks, and navigation locks. The models are a significant improvement over those which are currently used for design forces. The project will include significant involvement of Native Hawaiian undergraduate students, providing them opportunities to conduct summer research in Hawaii and also at OSU and Lehigh. Participation in this project, including the potential to carry out research at universities on the US mainland, will encourage them to pursue graduate studies and expose them to educational opportunities that they would otherwise not be aware of or not believe are accessible to them. The project involves international collaboration with two leading researchers in Japan on tsunami-debris hazards, one at Nagoya University and one at the Port and Airport Research Institute. Data from this project will be archived and made available to the public through the NEES data repository. This award is part of the National Earthquake Hazards Reduction Program (NEHRP).
As we have seen from videos and pictures of the 2011 Tohoku tsunami in Japan, the 2010 Chile tsunami and others, tsunamis pick up a lot of debris. This debris can pose a significant impact threat to structures that are in the coastal inundation zone. Prior to this project, such debris impact has not received much attention in the research community, and as a result building codes have been based on impact models that do not represent the actual physics. This project has filled the gap in knowledge and is leading to changes in the building codes to make our structures safer. The most common and significant tsunami debris relative to structural safety is woody debris (e.g., logs and telephone poles) and steel shipping containers, which can easily float. These high mass, relatively low speed debris can cause huge forces when they hit a structure. During this project, we conducted full-scale tests of a telephone pole (Fig. 1) and a shipping container (Fig. 2) swinging into a ‘structure’ at Lehigh University. The tests revealed that an errant utility pole can impact a structure with 100,000 lbs of force, while a shipping container can impart 220,000 lbs. of force. Data from these tests were used to validate numerical models for the impact forces. The models were developed at the University of Hawaii and at Lehigh University. Because full-scale testing of a shipping container in water was not possible, a one-fifth scale model was propelled by a ‘tsunami’ into a structural column in the Tsunami Wave Flume at Oregon State University, Fig. 3. These in-water tests let us understand that there are relatively small differences between water-propelled debris impact forces compared to those in-air. This allows engineers to make use of a much larger knowledge base when designing structures to resist tsunami debris impact forces. The data obtained from the experiments were used to confirm the accuracy of our numerical models. The models provide structural designers the forces they need to design buildings and other structures to survive debris impact. The models are being incorporated into building codes, and these new provisions will be more realistic than the old provisions. This will make our coastal infrastructure safer and more resilient. The results of this work are not just for tsunamis. They are also applicable for debris from flooding in rivers and flooding of coastal regions from storms like Hurricane Katrina and Hurricane Sandy. A number of undergraduate and graduate students have participated in this research, gaining useful research experience and making significant contributions to the success of the project. We have also published the results in engineering journals and made numerous presentations to the professional engineering community to publicize the important findings from this project.
