Abstract
大地震では,什器の破損や故障により医療施設が本来の機能を保持できず,医療活動に多大な支障をきたすことが懸念される。兵庫県南部地震では,兵庫県下の約3,100の医療施設のうち半数以上の約1,600施設が被害を受け,医療活動が非常に困難となった。その経験から,将来的に発生が予想される巨大地震に対し,医療施設の地震時の機能保持が強く求められている。しかし,医療施設内の什器に対する地震対策の基準や明確な方針は十分に示されていないのが現状である。学校や一般的な住居に関しても,家具や什器の移動や転倒により人身に危害が及ぶ危険性があり,それらが散乱した場合は避難の妨げとなる可能性がある。特に,長周期地震動に見舞われた高層建築物では,共振による被害の拡大が懸念されている。そのため,建物の倒壊を防ぐことと同時に,建物内に存在する家具や什器の地震時挙動を把握し室内の安全性を検討することは極めて重要である。さらに,家具等の転倒による人的被害の評価のためにはそれらの衝突時の速度や加速度を求める必要があり,家具等の断面力情報から人体に及ぼす衝突力を算出し人的被害を評価することも求められる。
To maintain the original function of medical facilities after earthquakes is important to avoid the increase of casualties. Furniture in schools and residences can become dangerous objects for human life, and many tumbled furniture such as chairs and tables can become fatal obstacles that prevent people from evacuating. Therefore, it is important to know the overturning behaviors of furniture under seismic excitations, as well as the behaviors and damages of the building itself. From this background, various shake-table tests for such specimen had been carried out, although such tests can be too costly to conduct repeatedly. To restrain the costs, numerical simulation techniques such as discontinuous element method (DEM) had been applied to investigate the motion behaviors of furniture. Its calculation cost is very small; however, there are physically uncertain properties that have to be fixed in the models and it is difficult to obtain the deformations and stress distributions of the models. The finite element method (FEM), on the other hand, is effective means to evaluate the deformations and stress distributions of the model and requires less number of parameters than the DEM.
The main objective of this study is to develop an effective numerical
code to analyze the motion behaviors of furniture subjected to seismic
excitations. The numerical code is constituted based on the ASI-Gauss technique,
which is a finite element scheme that provides higher computational efficiency
than the conventional code. In this code, frictional contact between objects
is fully considered by employing a sophisticated penalty method. In this
paper, two analyses using this code were conducted to achieve this objective.
One of them is a motion analysis of furniture in an office, and the other
is that of furniture in a medical facility. In medical facilities, there
are various furniture with casters. In the past huge earthquakes, furniture
with an unlocked caster moved fiercely and that with a locked caster overturned
instantly. We carried out some motion analyses of furniture with various
fixed conditions to clarify how the fixed condition of casters influence
the motion behaviors of furniture.
First of all, a motion analysis of furniture in office was carried out
to compare with the experimental results performed at Shimizu Corporation.
As a result, the overall behaviors of overturning motion in the analysis
were in good agreement with that of experiment. The finite element code
using the ASI-Gauss technique with frictional contact algorithm was thus
validated. Furthermore, the velocity and the sectional force of furniture
which are required to evaluate human suffering were obtained in the analysis.
Next, some motion analyses were carried out for furniture with casters
installed in the specimen of medical facilities, which was shaken at E-Defense,
NIED. In these analyses, the numerical method of expressing various conditions
of casters was employed. The fixed condition of casters can be varied using
this method and its influence on the motion behaviors of furniture could
be investigated. Furniture with casters such as an electric scalpel and
an operating table moved fiercely under a long-period ground motion. However,
furniture with locked casters and high center of gravity tended to rock
on the floor under a short-period ground motion. It was confirmed that
these motions strongly depended on seismic excitations, fixed conditions
of casters, and heights of center of gravity. From the motion analyses
of furniture in an office and furniture with casters in a medical facility,
the validity of the numerical code was verified.