Vertical evacuation:: Fleeing tsunamis by moving up, not out

grant from the National Science Foundation.

Though designing a brand-new building to withstand a tsunami would provide optimal protection from the onslaught of waves, it is often more economical to retrofit.

To retrofit buildings, engineers turn to computer models that combine principles of geophysics and structural engineering. The models can predict how a building will perform, depending on how strong the ground shaking is, how tall the tsunami waves are, the speed and direction of the waves when they hit and whether the flow is carrying debris, such as floating cars. The models also factor in the structure of the building — construction materials, the placement and strength of beams, columns and walls.

To enhance strength and stiffness, Deierlein said, engineers could make concrete columns or beams stronger and more ductile by retrofitting them with fiber-reinforced polymer composite overlays or concrete and steel jackets. Workers might add steel braces to the frame or construct walls that are reinforced to resist horizontal forces.

Walls in lower stories can be designed to break away under intense pressure from waves to reduce the stress on the building. These “frangible” wall systems, also found in hurricane-resistant buildings, are similar to windows that are designed to pop out under pressure. “It’s like wind blowing on a building,” Deierlein said. “Once windows pop out, wind can go right through.”

Another important consideration is the foundation, which should be protected from water that scours around the building. A tsunami could actually scour out so much of the ground around the building that it could be destabilized and fall over. Diversionary walls and berms could reduce this risk.

There is not a single magic formula, Deierlein said; instead, buildings have to be treated on a case-by-case basis. Given the high cost of retrofitting, some buildings deserve more attention than others. “The design depends on the everyday function of the building,” he said. “It’s OK if a warehouse gets damaged, but an emergency response center, a large school or large hotel could be used as an effective refuge place during tsunamis and should be designed to a higher performance level.”

To implement the latest research findings in developing countries, Deierlein and Stanford’s Blume Earthquake Engineering Center are partnering with the Stanford chapter of Engineers for a Sustainable World, a national nonprofit organization linking students with professionals, and a Palo Alto nonprofit organization called GeoHazards International, which aims to prepare developing countries for natural disasters.

They are collaborating with Indonesian government agencies to suggest recommendations for building design and educate engineering students at Andalas University in Padang. “We’re stepping up our efforts after the latest earthquake,” Deierlein said. “Working with the Andalas University is a key way to transfer knowledge and technologies to the future generation of engineering professionals in Indonesia.”

One challenge is training people to think about vertical evacuation. “Their instinct is to flee inland,” Deierlein said. “So we have to figure out how to educate people to have faith in buildings.” Most people see at most one tsunami in their lifetime, so they must rely on training rather than personal experience to change their habits.

Another approach is to make the most of people’s instincts. “We’re trying to understand what type of structures people would feel safe going to,” said Veronica Cedillos, a structural engineer and project manager at GeoHazards International. “For example, we heard about a lot of people going to mosques after a tsunami, so that’s definitely one of the main types of building we’ve been exploring as potential evacuation sites.”

No matter the strategy, Deierlein has faith that people in Padang will rise to the challenge. Developing countries have one advantage: They struggle all the time to survive,” he said. He recalls visiting a hospital while in Padang and asking if the emergency generator worked. The answer: “Of course. We use it several times a week.” “I was impressed with the resiliency of the city,” Deierlein said.

Still, he knows it is an uphill battle. “Developing countries have a long way to go to make the same improvements the U.S. has made in building design,” he said. “It’s important to reach out and look at problems facing developing countries, and to see how research and education can contribute to solving those problems.”