Unstable Behavior of Suspended Ceiling During Earthquake

Abstract eng:
In recent earthquakes, non-structural components such as ceilings were seriously damaged, while most structural frames of such buildings were not. It is no doubt that such ceiling damages should affect daily lives of residents thereof or prevent the use of such facilities for a certain amount of time. For this reason, it has been one of the most urgent issues to deal with. It should also be noted that such ceiling damages have been observed not only in Japan but also in other countries with earthquakes, where different construction methods for suspended ceilings were taken. Although it is clear that falling down of a Japanese-style ceiling is caused by detachment behavior of unique metal connection parts in steel furring, what made those connection parts detached has not been explained obviously yet. The construction methods of earthquake-resistant ceilings in Japan are categorized into two types, either with or without perimeter spacing. In case of a ceiling with spacing, braces are also set in order to prevent the ceiling from swinging, and an inertia force on the ceiling surface in an earthquake is transmitted to a main frame via steel furring and those braces. Due to such concentration of stresses, the connection parts near those braces are easily detached, if the parts do not have enough strength. On the other hand, in case of a ceiling without spacing, it is via points of contact between a ceiling surface and surrounding components like walls that an inertia force is transmitted to a main frame. Therefore, any extraordinary stress is not considered to act on the connection parts. However, some ceilings of this type did fall down due to detachment of connection parts in the past earthquakes. The cause of this detachment is not explained yet, even though many researchers have tried to simulate the failure of such ceilings by shaking table tests. In our presentation, we focus on dynamic behavior of ceilings without spacing, supposing any unstable behavior of ceilings should cause detachment of metal connection parts. Ceilings suspended by longer hanging bolts are especially discussed here, because in the former shaking table tests, the only test specimen was the standard ceiling with the same pitch and length of hanging bolts, and with the same layout of steel furring. In our numerical method, the Hertz model[2] and the master-slave model are applied in order to simulate the contact and release behavior of a ceiling surface to surrounding components. We present the numerical results showing that a ceiling with longer hanging bolts falls down due to detachment of metal connection parts while a ceiling with shorter ones is not fallen into an unstable condition. The different behaviors of ceilings with shorter and longer hanging bolts agree well with the actual damages done to ceilings in the past earthquakes.

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