Long-period seismic ground movements of the sort that struck Tokyo and Osaka during the Great East Japan Earthquake pose a serious threat to the framework of high-rise buildings, scientists have confirmed.
Long-period seismic ground movements of the sort that struck Tokyo and Osaka during the Great East Japan Earthquake pose a serious threat to the framework of high-rise buildings, scientists have confirmed.Experiments using scale models by researchers at the National Research Institute for Earth Science and Disaster Prevention showed that the long, slow ground motions can lead to significant deformation of the structure of a 80-meter, 21-floor tower block after four minutes.Force was concentrated on welded connections between the columns and beams and rupturing was observed at some of those points.The results of the experiment at the institute's Three-Dimensional Full-Scale Earthquake Testing Facility, dubbed E-Defense, in Miki, Hyogo Prefecture, were announced on March 8 at a presentation of research for the science and technology ministry at the University of Tokyo.Although the columns and beams made up the basic framework of a high-rise, the rupturing of some connections would not be expected to lead to an immediate collapse because of the large number of welded parts connecting the columns and beams. However, that damage would weaken the building and make major repairs necessary.The experiment showed that rupturing could be prevented by reinforcing the welded parts or by installing technology to reduce the swaying of the building.The experiment simulated seismic waves with long-period ground motions that are expected to hit Nagoya if the predicted Tokai and Tonankai earthquakes strike at the same time.Computer modeling had raised the possibility of long-period ground motions undermining the framework of high-rise buildings. However, because of the difficulty of modeling the strength of the building materials and welding technology used in particular buildings, the latest experiment gave greater detail on the extent of possible damage.During the Great East Japan Earthquake, long-period ground motions struck high-rise buildings in the Tokyo and Osaka areas. There were many reports of damage, including falling ceilings, which did not directly affect the framework of structures.