Axelrod Explores Isolator Device that Protects against Earthquake Damage

February 1, 2007

AxelrodCivil and environmental engineering major Nicole Axelrod’s research as a Pratt Undergraduate Research Fellow could lead to improvements in the design of devices meant to limit damage to sensitive equipment during an earthquake.

In the laboratory of CEE Professor Henri Gavin, Axelrod works on simulated versions of the ISO-Base™ Seismic Isolation Platform, a commercially available product made by the southern California-based company WorkSafe Technologies. The platform consists of a steel ball sandwiched between two load-bearing plates with recessed areas, or dishes, on their inner surfaces, the native of south Florida explained.

“This unique design allows the platform to roll smoothly and evenly while accepting input ground accelerations from any direction,” according to WorkSafe Technologies’ website. When the earth stops rumbling, the device naturally gravitates to its original position. The device is already being applied for earthquake protection of everything from supercomputers to hospital equipment.

But could the isolators be made even better?

It’s Axelrod’s goal to find out. She is testing whether design tweaks -- in particular, changes in the shape of existing isolator components or the addition of new components -- might improve the platform’s performance.

First, Axelrod gathered some basic parameters through experiments conducted on a shaker table that could mimic the shifting ground characteristic of an earthquake. She measured the movements of two platforms with respect to two parallel cylinders cushioned between them with foam.

She then created a computer model of the isolator to examine how its behavior would change with variation in the design.

“I relied on the basic force moment reaction equations,” she said. “I change one thing at a time and see how it affects things.” For example, she tested a parabola-shaped dish compared to the cone-shaped dish now employed.

Their primary focus now, however, has shifted to foam--a component the current ISO-base model does not include.

“We’re testing different damping coefficients for foam, to see how the system reacts,” Axelrod said. “There isn't any foam on the current ISO-base product, so that's the main thing that we're hoping to influence with the study--to show that damping the motion of the ball in the cone will help improve the performance of the isolator.”

Gavin and Axelrod ultimately aim to influence the actual product, a goal that will provide plenty of fodder for future Pratt Fellows to come, she said.

A native of Coral Spring, Fla., Axelrod initially enrolled at Duke as a Trinity student, before realizing that her interests were better suited to engineering. She particularly appreciates the small class sizes typical of the CEE department and the ease with which students can obtain a certificate in architecture. She said her experience with hurricanes in Florida has fueled her interest in engineering for natural disasters. She has participated in the American Society of Civil Engineers Carolinas Conference concrete canoe and steel bridge competitions, and plans to pursue a job with an engineering firm in her home state after graduation.