Motion Analysis of Earthquake-Resistant and Non-Resistant Ceilings under Seismic Excitation


 As buildings with large-scale spaces such as school gymnasiums are used as refuge bases in disasters such as earthquakes, they are required to be usable afterwards and are also required to resist aftershocks. However, in the Great East Japan Earthquake, cases had been reported in which gymnasiums did not satisfy the function as refuge bases due to falling of ceilings and lightings. Therefore, we should take measures to prevent ceilings from falling and in order to apply effective earthquake-resistant measures, it is necessary to know the collapse mechanisms of the ceilings.

In this presentation, the difference of the behaviors under seismic excitations was confirmed by conducting several motion analyses of earthquake-resistant and non-resistant ceilings. Two kinds of numerical models representing the ceilings were constructed. The non-resistant ceiling is composed of hanging bolts, ceiling joist receivers, ceiling joists, and plaster boards. The components are connected with some metal fittings. For example, hanging bolts and ceiling joist receivers are connected with hangers, and ceiling joist receivers and ceiling joists are connected with clips. Furthermore, ceiling joists and plaster boards are connected with screws. The earthquake-resistant ceiling, on the other hand, has some additional braces to suppress the motion. Also, a clearance is provided between the ceiling and the wall. Clips used for the earthquake-resistant ceilings have stronger connections than those used for non-resistant ceilings. For the numerical analysis, all the members were modeled using linear Timoshenko beam elements and the adaptively shifted integration (ASI) - Gauss code was used. The detachment and collapse of ceilings were considered by introducing detachment criteria into the metal fittings that were obtained from some preliminary tests.

Simulation was performed by applying a seismic wave observed during the Great East Japan Earthquake to the ceiling models. According to the numerical results, non-resistant ceilings swayed greatly and collided with the wall. The metal fittings detached occasionally during the impact. The ceilings fell at the parts where numerous metal fittings detached. On the other hand, any of the metal fittings did not detach and the ceilings were all safely installed in the case of the earthquake-resistant ceilings. The earthquake-resistant ceilings had never collided with the wall, which owes to two main reasons; suppression of motion by the additional braces and the large clearance by the wall.

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