The Arc of an Idea

Dr. Li
June 07, 2018

After buildings and infrastructure are damaged by an earthquake, they have to remain closed until building officials can assess the integrity of the structure. In the case of massive earthquakes that cause widespread damage, this process can take months, temporarily leaving millions of people without lodging or access to other buildings.

Dr. Pedro Silva has developed a hypothesis about a novel shear wall design that he believes will mitigate damage from earthquakes, thereby decreasing the number of buildings that have to be closed following an earthquake. He will soon begin testing his design in the Science and Engineering Hall’s high bay.

When a typical shear wall is constructed it is cast as a unit with the wall’s footing. This construction has its advantages, but it limits the wall’s ability to dissipate energy from the earthquake, so the damage to the wall often creates permanent deformations in the building, causing the building to be closed after an earthquake. To address this problem, engineers more recently have proposed decoupling the wall from its footing, creating what is called an unbounded post-tensioned shear wall, or UPSW. Unfortunately, the standard UPSW design creates a design disadvantage of its own.

“The limitations of UPSW design are that a structure that experiences less damage experiences higher levels of wall displacement, which can affect non-structural components like windows and doors,” explains Dr. Silva. “So, you can still come to work because it will be safe, but you might not have windows, for example.”

To limit this non-structural damage, some engineers have proposed incorporating energy dissipation devices into the UPSW design; however, the devices are for one-time use, so the building will not remain resilient if it sustains after-shocks or subsequent earthquakes. But what if the UPSW design—which limits structural damage to the building—could be altered to allow the wall to dissipate unlimited amounts of energy time and time again?

Dr. Silva believes he has found a solution for that. He proposes changing the interface between the wall and the footer from a flat surface to a curved surface. “With this approach, the amount of energy that can be dissipated has been proven numerically to be far superior to a flat wall. It reduces the displacement of the wall by a magnitude of 10 times less than the UPSW with the flat construction,” claims Dr. Silva.

To test his hypothesis experimentally, Dr. Silva plans to build two types of models in the high bay—one with a single wall and one with double walls—and submit them to forces that simulate an earthquake. He is confident, however, that the experimental results will confirm his hypothesis. “If the experimental tests can confirm the numerical results, this will give engineers the confidence to implement this system into design practice,” he notes.