Tsunamis can strike with little warning, but walls of water are not the only danger. Another potentially lethal challenge is water-driven debris – loaded cargo containers, barges, or vehicles – transformed into projectiles that crash into buildings. A compromised structure can endanger those seeking safety within it.
A multi-university team lead by Ronald Riggs, a structural engineer at the University of Hawaii, has determined the potential impact and will present findings at an international conference in June. The goal is to supply structural engineers with information to design buildings in areas vulnerable to tsunamis.
Of most concern are shipping containers, which can weigh up to 6,000 pounds when fully loaded.
These containers that line port areas well exceed the default telephone-pole-size 1,000-pound log assumed by the majority of U.S. building design guidelines.
"Most structural systems are designed to defy gravity, not a side kick from a shipping container," Riggs says. "They may only be moving about 10 miles an hour, but given their weight, this is a significant load for a structure not made for it. An engineer can build what it takes to withstand the karate chop, but first the engineer has to know what forces to expect."
During research trials, Riggs and his team were surprised to learn that water didn't increase the force of impact because contact lasted for a matter of milliseconds.
They also found that the damage from an empty container vs. a fully loaded one was essentially the same.
The next step for the researchers 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 U.S. West Coast 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 problematic."