木質床の動的変形挙動(II) : 釘接合部の剛性低下に関する要因

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木質床は，歩行等によって繰返しの衝撃的荷重を受ける機会が多く，そのような動的荷重には床材や根太などの力学的性質，接合の形態や条件などが関わって，釘の弛援や床材の疲労などの複雑な挙動を併発し，損傷を起こす．そこで，床構造体の釘接合部の剛性だけでなく，複合的に起こる力学的現象を把握し，その機構を明らかにする必要があると考えられる．本報告においては，前報にひきつづき，釘接合木質床の接合部の剛性におよぼす要因，とくに根太の変形，釘の引き抜き抵抗，および衝撃荷重の繰返しについて，単純モデルによって実験的に検討した．その結果，根太の変形は，床材との接触面に近いほど大きく，とくに永久変形としての圧潰は，衝撃エネルギを吸収し釘の引き抜けを抑制する効果があることを明らかにした．しかしながら，その効果は極端に軽軟な材においてのみ顕著であり通常の根太材においては無視し得る．また，釘接合部の剛性は，釘の引き抜き抵抗に正の相関があり，釘の引き抜き抵抗が接合部の剛性を支配する主な要因であることが認められた．さらに釘接合体が，比絞的大きな衝撃力での繰返し増加は，釘の引き抜け量を増大させるぼかりでなく，接合部の剛性を低下させることを把握した．Some simplified specimens for wood-based floors fastened with common nails were tested by repeating dynamical bending load in order to analyze the factors related to rotational stiffness in nailed joints, particularly, edge deformation and crushing of wood joist, nail withdrawals, and the number of loading cycles. Results were obtained as follows : 1) In wood joist, the portion near tile interface with subflooring. i. e., the upper edge of wood joist showed the greater deformation and crushing than the portion far from the interface. Because of this behavior of absorption of the impact energy generated by the applied load, nail withdrawal was limited to small. This effect was clearly shown for the wood joist with extremely low density. However, it was shown that such effect was negligible For the wood having a common density in wood constructions. 2) Rotational stiffness and withdrawal resistance of nail showed very high correlations, that is, withdrawal resistance is one of the important factors related to rotational stiffness in nailed joint. 3) Under repeating the dynamic load, the decrease of rotational stiffness of nailed joint was great during the initial stage of loading cycles and associate with the increase of nail withdrawal. However, the rate was decreased very last as to the number of loading cycles increased.
九州大学の論文

木質床の動的変形挙動(II) : 釘接合部の剛性低下に関する要因

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