ASI-Gauss法に基づく吊り天井脱落挙動解析による耐震対策の有効性評価

抄録

　One of the ways to mitigate earthquake damage due to suspended ceiling collapse is to improve earthquake-resistant performance of the ceilings. In E-Defense, shake table tests were conducted for a structural frame assuming a school gymnasium with seismic ceilings designed in accordance with the technical standards. The experimental results showed that the specimen had enough earthquake-resistance performance for the assumed seismic excitations. However, in this experiment, it had not been clarified how several seismic countermeasures applied to the ceilings work under seismic excitation. In other words, although the seismic performance had been verified, it was not clear how the countermeasures work to prevent the ceilings from damage. Therefore, it is necessary to evaluate function and effectiveness of the countermeasures in detail.

　In this study, we conducted seismic response analyses of gymnasiums with different earthquake-resistance countermeasures to investigate effectiveness of three types of countermeasures, that is, seismic braces, clearance and reinforced joint metals. The finite element method incorporating the Adaptively Shifted Integration (ASI)-Gauss technique were used to simulate suspended ceiling collapse. In the previous paper, it had been confirmed that the proposed simulation method can accurately reproduce behavior and collapse of non-resistant suspended ceilings.

　Here, firstly, we validated the numerical model of earthquake-resistant ceilings through reproduction simulation for the shake table test of the specimen with earthquake-resistant ceilings introducing all three countermeasures. As a result, detachment of joint metals and collapse of ceilings were not observed at all as in the experiment. Also, response acceleration and displacement were in good agreement with the experimental results.

　Secondly, we investigated the effectiveness of each countermeasure. In the case with only seismic braces, ceilings collapsed in larger area than without any countermeasures. That was because response acceleration increased as the braces stiffen the structure. According to the result in the case only with clearance, ceilings collapsed in a similar way as the non-resistant ceilings, though the ceiling collapse near the walls due to collisions between the ceilings and the walls was observed only in this case. In the case only with the reinforced joint metals, only slight damage occurred near the ceiling top, and a proposed detachment risk index of clips significantly reduced in the whole area. Also, it was confirmed that the case installing both seismic braces and reinforced joint metals had almost the same seismic performance as the case with all three countermeasures.