Making buildings more tsunamis-resilient
for it.”
His colleagues and he proposed research to analyze several pieces of the puzzle with the help of the George E. Brown Jr. Network for Earthquake Engineering Simulation(NEES), a distributed laboratory with fourteen sites across the United States funded by the National Science Foundation. The network, which also funded Riggs’ research, provides access to highly specialize, sophisticated, and expensive equipment.
For Riggs, two NEES sites were needed. One is at Lehigh University in Bethlehem, Pennsylvania, which specializes in real-time multi-directional testing for earthquake simulation of large-scale structural systems. The other is a wave flume longer than a football field at the Tsunami Research Facility at Oregon State University. At the Lehigh site, they swung full-scale wooden poles and shipping containers through the air on a pendulum to determine the force of impact at various velocities. At Oregon State, they ran similar tests at a 1:5 scale, but this time in its large flume wave to see if that made a difference.
His basic assumptions held true, but there were two surprises. First, when the speed of the projectile was the same, the water did not have a significant impact.
“We thought the fact that it was in water would increase the load, but it did not, at least not substantially,” Riggs says. “The impact is so short, on the order of a few milliseconds, that in some ways the water doesn’t have time to increase the force.”
The second surprise was that the weight of the shipping container’s contents also did not matter as much as he would have expected. The container itself, which is roughly 20-feet long and weighs about 5,000 pounds empty, could weigh as much as 60,000 pounds when fully loaded. Yet, its load when striking a building was not significantly greater than that of the empty container.
The reason is the same as for the water, Riggs says.
“Unless the contents are rigidly attached to the frame of the container, which they usually are not, the contents also don’t have time to increase the force during the very short duration of impact.”
The next step for Riggs and his team is to use the preliminary findings to better define building guidelines and policy.
“It’s especially important for areas like Japan and the Cascadia area on the West Coast of the United States where tsunamis are most likely to strike with little warning, making vertical evacuation essential,” Riggs says. “Or in Waikiki where the population density would make horizontal evacuation (trying to outrun the tsunami) problematic.”
Riggs will present the team’s findings at the 32nd International Conference on Ocean, Offshore and Arctic Engineering, sponsored by the Society of Mechanical Engineers(ASME) to be held 9-14 June in Nantes, France.
His colleagues are Clay Naito, associate professor at Lehigh University; Dan Cox, professor at Oregon State University; and Marcelo Kobayashi, associate professor at the University of Hawaii.
