ASI-Gauss法を用いた骨組構造の火災崩落解析
Fire-Induced Collapse Analysis of Framed Structures Using ASI-Gauss Technique

Abstract


2001年9月のNY世界貿易センター(WTC)ビルの完全崩壊は,世界中を震撼させた.FEMAおよびNISTの調査報告書では,WTCビルの崩壊は航空機衝突後の大規模火災が主原因で起きたとしているが,例えば延焼範囲の規模や柱・はりの変形挙動がタワー全体の強度に与えた影響や,崩壊時の落下速度が飽和速度に近いとされた原因について,調査が十分に行われたとは言い難い.本研究では,骨組構造の崩壊解析に有効なASI-Gauss法を火災崩落解析に適用し,建物全体の設計強度や部材接合強度,火災の発生範囲などがその後の崩壊挙動にどのような影響を与えるか検証した.破断判定には,実験データに基づいた部材接合部の破断臨界値を採り入れた.また,火災による温度上昇に伴う熱膨張および部材耐力(ヤング率,降伏応力)の低下を考慮した.設計強度(柱の太さ2種類),部材接合部強度(強弱2種類),火災パターン(3種類)を組み合わせ,25層高層モデルで火災崩落解析を実施した結果,強度が弱いと崩壊しやすいこと,火災パターンによっては強度が強くても崩壊する可能性があることなどが確認されたので,ここに報告する.


An adaptive finite element code using linear Timoshenko beam elements called the adaptively shifted integration (ASI) technique and its modified version, the ASI-Gauss technique, have been applied to various numerical simulations on the collapse of framed structures. One of its recent applications was a full model simulation of the aircraft impact with the New York World Trade Center (WTC) Tower 2 in 9/11 terrorist attack in 2001. According to the simulation, springback phenomena due to rapid unloading occurred in the core columns during the impact, which might have caused the destruction of member joints. In this paper, we performed another simulation to investigate the effect of fire occurred in a high-rise tower. The results clearly show the effect of the weak member joints, which were reported to be 20 to 30 % of the strength of the members in WTC towers, and also the effect of the strength reduction due to elevated temperatures.


PDF file