Reminders Of Earthquakes PastPublished: May 15, 2014
This year, California is vibrating with earthquake anniversaries and Civil Engineering’s Lisa Star, an expert on geotechnical engineering and soil-structure interaction, knows them by heart.
The Loma Prieta earthquake marked its 24th birthday this fall after shaking the state for 10-15 seconds on Oct. 17, 1989. The Northridge Quake recorded its 20th anniversary since shuddering its way into the history books for 10-20 seconds on Jan. 17, 1994. The second-worst earthquake in recorded history rocked Alaska 50 years ago for four minutes on March 27, 1964.
Star, who joined the Civil Engineering and Construction Engineering Department in 2011, sees plenty of advantages to her performing her soil-structure interaction research in southern California.
“Two of the best places for geotechnical engineering are California and Japan,” she said. She pointed to the 10-second March 1933 Long Beach earthquake that claimed 115 lives. Just one month after the earthquake, the California State Legislature enacted the Field Act. “This was the first earthquake to spur engineers to design buildings with earthquakes in mind,” she explained.
Structural engineering has come a long way since 1933. “In the old days, a structural engineer would visit a building site and make an estimation,” she said. “But then, modeling got more sophisticated and structural engineers found that their models did not match what was going on. We have come to understand the importance of the interaction between soil and structure.
“For instance, there is a difference in loads,” she added. “A static load just sits there. If the load is heavy, it compresses down the soil. If you pile more and more pancakes on a plate, the pancakes get squished. Soil does the same thing under a big load. But an earthquake applies a dynamic load that changes. In an earthquake, the loads are horizontal and move sideways.”
A world-famous example of static load is the Leaning Tower of Pisa.
“The tower is interesting because the soil on one side is softer than the soil on the other side. The tower squishes the two sides differently,” she said. “The softer side settles more and the harder side doesn’t. Today, they try very hard to make the tower tilt in a particular way. They can’t put it right or else they wouldn’t have a tourist attraction.”
One of California’s best examples of the effects that earthquakes can have on structures is found in the city of San Francisco. “The San Andreas fault runs right by it. What is interesting about San Francisco is its reclaimed land,” she said. “Some of the older building sites were filled with whatever was handy at the time. Once they were filled with garbage, San Franciscans decided they could build on it. That is a big challenge. They are prone to what we call ‘liquefaction.’ Think of liquefaction as quicksand because it behaves in exactly the same way.”
More than earthquakes can liquefy the earth as the Philippines can testify. Super Typhoon Haiyan made the city of Tacloban resemble a garbage dump with only a few concrete buildings left standing after 147-mph winds whipped up 20-foot walls of seawater.
“Hurricanes, tsunami loading and wind loading all came together there,” Star said. “Sometimes structures must face combined natural disasters. Add to that laxly enforced building codes and you have a disaster. Look at the impact of Hurricane Katrina in 2005 on New Orleans. They had perfectly modern building codes but they still had big problems. In the 2011 Tohoku earthquake off Japan, a tsunami was triggered that reached heights of up to 133 feet and traveled up to six miles inland. Japan suffered serious damage despite having some of the most stringent building codes in the world.”
Star received her B.S. in civil engineering (2006), her M.S. in geotechnical engineering (2007) and her Ph.D. in geotechnical engineering (2011), all from UCLA.
One industry keenly interested in soil-structure interaction is nuclear power. “Stiffer, stronger buildings have more effects from soil-structure interaction. Nuclear power plants are built like bunkers,” she said. “Following the Japanese tsunami, all U.S. nuclear facilities were ordered inspected. That is especially true for the California facilities that we know are most exposed to earthquake loading such as Diablo Canyon and San Onofre.”
The science of structure-soil interaction has come a long way since Venice and St. Petersburg built themselves on logs hammered into the earth. “Today, we have a much better understanding of what’s going on. We use computers to create sophisticated modeling. That has been a big breakthrough,” she said.
Knowing what she knows changes the way Star sees the world. “It’s true you can’t look at a building and say, that’s doomed,” she said. “It takes a lot of time and energy to perform an investigation and today, with the help of high technology, I can stand back, look at a building and say, ‘That’s so cool! Look what they did!’”