Isbiliroglu Models Buildings’ Behavior During Earthquakes
When Yigit Isbiliroglu (CEE PhD ’13) looks at buildings, he sees details others might not notice. Isbiliroglu, who belongs to an inter-departmental team of CMU researchers known as the Quake Group, studies the way buildings behave during earthquakes. He recently published a paper that presents his latest accomplishments in earthquake modeling. His latest paper, Coupled soil-structure interaction effects of building clusters during earthquakes, presents his latest accomplishments in earthquake modeling and was recently accepted for publication in Earthquake Spectra. The paper is co-authored by Ricardo Taborda (CEE PhD ’12), Assistant Professor in the University of Memphis’ Center for Earthquake Research & Information, and by Jacobo Bielak, Isbiliroglu’s advisor and the Paul Christiano University Professor of Civil & Environmental Engineering.
When an earthquake occurs, each building feels the impact differently depending on the structural rigidity of the building, its foundation, and the surrounding soil. The motion of the ground between and around buildings may also vary widely. Isbiliroglu wants to know how the arrangement of a group of buildings could affect the severity of the earthquake’s effects on buildings. “The basic approach until now has been to study buildings in isolation,” he explained. “That gives you some idea of how a particular building will behave in an earthquake, but as cities evolve and closely spaced, high-rise buildings are constructed in city centers, we also need to understand the interactions between buildings through the ground.”
With funding from the National Science Foundation, Isbiliroglu’s team simulated the ground motion of the 1994 Northridge earthquake, whose close proximity to densely populated Los Angeles metropolitan area made it the costliest earthquake in U.S. history. They then created simplified models of buildings in a section of the San Fernando Valley and compared the behavior of a group of buildings during the earthquake to that of a single building. “Because we put everything into a single simulation, every part talks with each other: the earthquake source, the ground, and the buildings,” he said. “It is a more complete representation of reality.”
One might think that clusters of buildings are beneficial during an earthquake because the motion is distributed among the buildings, lessening the severity of the overall effect. However, Isbiliroglu’s team is exploring several factors that might determine how a building will fare during an earthquake. The number of buildings, their dynamic properties (or ability to “bend”), and the distance between them all dictate the maximum ground motion underneath them. The team has found that in some cases, the ground motion between buildings may actually be stronger because of variation in these factors, which in turn can affect the demand on some of the buildings themselves.
Their study will be key in expanding engineers’ and city planners’ understanding of the way earthquakes affect cities. “Ours is the first truly three-dimensional study done using a realistic seismological background model for studying how multiple interactions between buildings can affect the ground motion and the structural response of buildings,” Isbiliroglu said.
The simulations of the earthquake and the building cluster response were conducted using Kraken, an aptly named supercomputer located at the National Institute for Computational Sciences at the University of Tennessee, Knoxville. It took 15,000 processors running for fifteen hours to simulate the regional response of the ground during the Northridge earthquake and the dynamic behavior of a family of different building clusters, an achievement whose magnitude is not lost on Isbiliroglu. “Prior to coming here, I never imagined this was possible,” he said. “We can take a volume of 100 kilometers cubed, model it, and use supercomputers to simulate a real earthquake, and then compare it with the observations with good results. To have such a tool amazes me.”
There is a special reason for Isbiliroglu’s interest in earthquakes: Turkey, his native country, is prone to them. He noted that earthquake engineering is a popular research topic among civil engineers in Turkey, adding, “I always planned to get an advanced degree in earthquake engineering, with the idea that in the future I may be able to help Turkey construct more sound buildings.”
Isbiliroglu completed his PhD in September and will be joining Paul C. Rizzo Associates in Pittsburgh as an Engineering Associate. He hopes that city planners can use his research as a resource when developing building codes, saying, “Often, you see two buildings that are identical in dimensions, yet in an earthquake, one collapses and the neighboring one stays intact. We are helping to explain such things.”