Tremors lasted only 20 seconds during the disastrous 1995 Kobe earthquake. However, the city was close to the epicenter and hit by the strongest tremors, causing casualties in the thousands and over $150 billion in damage. Even though the Japanese government increased its spending on earthquake-resistant building structures and disaster prevention planning has improved, many questions remain.
Assistant Professor Wassim Ghannoum is working with Japanese investigators at the National Research Institute for Earth Science and Disaster (NIED) E-Defense shake table facility to advance research on preventing structural system failures. The E-Defense (Earth-Defense) is the world's largest earthquake-shaking table and can support real-life building specimens weighing up to 2.5 million pounds.
In 2010, two full-scale, four-story reinforced concrete (RC) buildings were tested under increasing multi-directional seismic excitations to near collapse. The ground motions used were recorded during the devastating 1995 Kobe earthquake. This test series is the only one to date in which full-scale, multi-story RC buildings were subjected to all components of recorded ground motions to near-collapse damage states. Ghannoum, other U.S. researchers, and Japanese investigators collaborated on the design and instrumentation of the building specimens which took place at the facility.
The test program intends to shed light on the full system performance of modern buildings built in accordance with today’s seismic design codes and find ways to improve the safety and damage-resilience of such structures when subjected to extreme earthquakes.
WATCH VIDEO of full-scale concrete buildings under extreme earthquake shaking on world’s largest multi-directional shaking-table.
WATCH VIDEO of reinforced concrete buildings subjected to ground motion.
The results showed severe damage to shear walls and beam-column joints and loss of integrity. Even though these structural systems were designed according to current earthquake engineering practices, the team’s observations raised serious questions about current seismic design codes and construction practices.
Since the shaking table tests produced a wealth of data from which lessons can be learned, Ghannoum is now tasked with performing in-depth analyses. His current National Science Foundation (NSF) funded project, “Behavioral and Analytical Investigations of E-Defense Shaking Table of an RC Structure,” aims to uncover the causes of this performance and provide recommendations for improvements in analysis and design practices.
“The project focus is on understanding the behavior of modern reinforced concrete buildings during extreme earthquakes and advancing simulation capabilities that are critical to the design process. We now have a good handle on the behavior of the tested structures and are currently evaluating the accuracy of advanced analytical models. The end goal is to propose our own analysis tools that best simulate the seismic behavior of reinforced concrete buildings,” says Ghannoum.
As the project’s PI, Ghannoum’s objectives are to assess the validity of current behavioral knowledge and design codes in light of the experimental program, assess the accuracy of the current analytical methods for this common type of structure, and to recommend improvements on behavioral and analytical fronts.
In addition to strengthening ties with E-Defense researchers, he will also incorporate new knowledge into his graduate course, which covers the behavior of reinforced concrete structures. Civil engineering graduate student and teaching assistant Jinhan Kwon is also working with the team.
Ghannoum is the chair of the American Concrete Institute’s committee on Seismic Repair and Rehabilitation and was on EERI’s committee coordinating technical assistance to Haiti.
