On July 14, 2009, a six-story condominium building shook with the earthquake motions of the 1994 Northridge quake, but one and a half times as intense--more powerful than any earthquake California has experienced in modern times.
The final experiment of National Science Foundation's (NSF) multi-year NEESWood project, the effort tested new ways to construct buildings that can withstand severe forces of nature.
NEESWood set out in 2005 to study how wood-frame structures--those consisting of mostly wooden parts, as opposed to concrete and steel--respond to the shaking of earthquakes. Wood-frame construction can be more affordable for mid-rise buildings than other methods, but little is known about how such buildings respond to earthquakes.
Using the 1988 Uniform Building Code as a guide for construction, the project engineers used the resulting test data to develop computer models that may help designers predict how wood-frame buildings will fare in an earthquake.
For the final experiment, project engineers worked with industry to develop a condominium building that has the design and detailing necessary to withstand forces that exceed even those in current safety specifications.
The final design, which included a seventh concrete and steel story that represented attached retail shops, underwent three days of testing, each resulting in a trove of valuable data about how structures can weather earthquake assaults. In total, the wood-frame component is 1,400 square meters (14,000 square feet) of living space composed of 23 residential units (both one- and two-bedroom designs).
Working with the Japanese government's National Research Institute for Earth Science and Disaster Prevention (NIED), as part of a broader partnership with NSF, the NEESWood engineers tested their structure at E-Defense. The facility, located in the city of Miki, north of Kobe, houses the world's largest shake table.
On June 30, the entire, sensor-laden structure experienced two tests--one simulating earthquake forces that occur, on average, once every 72 years, and a second that would occur similarly once every 475 years. On July 6, the same tests were run, but the steel-frame components was locked down, so only the six-story, wood-frame, residential structure was affected.
After repairs, on July 14, the structure became the subject of the largest shake-table test the world has seen to date: six storied, all-wood construction, shaken to motions from the 1994 Northridge earthquake, amplified to a level that equates to an event that occurs, on average, once every 2,500 years.
In this NSF Webcast, see the final NEESWood shake test and hear how the results were used to save lives. The webcast transcript
Credit: National Science Foundation