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Lessons Learned from Japan's Earthquake

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Mark Aschheim (center, in hard hat) joins fellow earthquake engineers in Japan.

Mark Aschheim, chair of the Department of Civil Engineering and member of the Earthquake Engineering Research Institute traveled to Japan this summer with a team of earthquake engineers led by Prof. John Wallace of UCLA to perform earthquake reconnaissance for the NSF-funded Learning from Earthquakes program. As a member of the buildings team, he spent a week in the Fukushima and Sendai areas investigating damage to reinforced concrete buildings incurred as a result of the devastating March 2011 quake. Faculty from the Univeristy of Tokyo and Tohoku University organized the week-long visit on behalf of the Architectural Institute of Japan (AIJ).

“We were in the field every day assessing the damage caused by ground shaking,” said Aschheim, whose research focuses on developing techniques for performance-based seismic design. “We saw fairly typical failures of reinforced concrete columns, in particular. It was apparent that while some areas had higher concentrations of damage due to softer soils; elsewhere affected buildings were relatively far apart from each other and only the most vulnerable buildings suffered serious damage.”

Aschheim notes that those buildings that had used “stiff” retrofits (with diagonal braces and in-fill shear walls) had negligible damage. This was in contrast to a retrofit that had employed viscous dampers, which caused “those columns to undergo larger displacements and suffer substantial damage, although less than would have occurred without the retrofit,” he said.

“It’s an illustration of what is obvious from an engineering point of view, however, it’s good to have field validation that control of deformation matters,” he said, continuing “There is a subtle but big paradigm shift that is happening in earthquake engineering today. In the past, the focus wason keeping buildings from collapsing, and ductile structural systems were the most prized. Now we need to address the fact that ductility [the ability of a material to stretch or deform rather than fracture] implies damage; we need to focus first on tolerable damage levels and then on the structural systems that can deliver the desired performance.”

Aschheim cites as an example the response of two hospitals to the earthquake in Japan. One facility was constructed with steel moment resisting frames and several wings of the facility were heavily damaged from the deformation caused by this flexible and ductile system. “This was a relatively new hospital that needed to be operational after the earthquake, but was severely impaired by damage. Another nearby hospital, which had used a base isolation system, responded so well that surgery continued unimpeded during the earthquake.”

Seeing first-hand how Japan’s reinforced-concrete structures weathered the temblor is important for earthquake engineers here in the United States. “Observing the aftermath of an event such as took place in Japan last spring is extremely valuable,” said Aschheim, “It helps us understand how to better mitigate damage and manage risk from such a devastating occurrence.”