模態側推分析應用於預力自復位鋼構架系統之耐震能力評估

Abstract

本研究主要為探討以靜力之模態側推分析應用於三、六、十二樓兩跨預力構架之耐震能力評估，本研究首先以兩個預力構架模型做比較，一為旋轉彈簧模型(RS model)、另一為軸向彈簧模型(AS model)，在三、六樓構架於位移與層間側位移角差距在10%以內、十二樓構架低樓層差距達75%，其主要原因為AS模型之梁剪力會造成柱底額外的彎矩產生，而在RS模型無法模擬，故在越高樓層可看出梁剪力影響越大、RS與AS模型在動力分析下之鋼腱內力增量差距很大，在十二樓構架一樓處有無窮大的差距，其原因為當AS模型無鋼腱內力增量(0 kN)時，此時RS模型有鋼腱內力增量會造成差距至無窮大、而兩模型因計算柱束制力之方式不同，故在某些樓層會有較大的差距，而造成如此大的差距主要原因為該樓層之柱束制力很小會使得差距放大，且當兩模型柱束制力拉壓力不一致時會造成差距有小於-1的值，使圖形看似無規則，反之，在柱束制力較大的樓層兩模型之差距就不會相差太大。雖鋼腱內力增量與柱束制力差距很大，但其差距的量值對於初始預力最大分別佔約20%、10%，故在評估梁軸力時，兩模型最大差距在十二樓構架也僅約23%。兩模型於十二樓構架有大的差距，但在三、六樓在位移、層間側位移角與梁軸力差距皆很小，故本研究先不考慮兩模型固有的差距而使用模態側推分析於較簡易的旋轉彈簧模型來評估模態側推的可行性。模態側推分析於旋轉彈簧模型上在位移(三、六樓構架最大差距於約5%，十二樓構架最大差距在中間樓層約10%)與層間側位移(三樓構架最大差距約10%，六、十二樓構架最大差距約20%)有好的評估能力，而在鋼腱內力增量(三樓構架頂樓最大差距約40%、六樓構架頂樓最大差距約30%、十二樓構架在頂樓處最大差距約65%)與柱束制力評估上有大的差距，但預力構架系統之梁軸力為初始預力、鋼腱內力增量、柱束制力以及側推力或慣性力所產生的梁桿件軸力所組成，即使鋼腱內力增量以及柱束制力有較大的差距，但在考慮整體梁軸力時，此較大的差距對於整體梁軸力的影響很小(三、六樓構架梁軸力最大差距約10%、十二樓構架梁軸力最大差距約20%)。

This research is investigating the modal pushover analysis (MPA) for estimating seismic demands of 3, 6, and 12-story steel post-tensioned self-centering frames. First, comparing the behavior of RS model and AS model under the ground motion. There has a large error in 12-story frame at the lower floor (75%) on displacement and interstroy drift, but has good estimation of 3 and 6-story frame (10%) on displacement and interstory drift. In strand force increment, at the 12-story frame lower floor has infinite error. The reason is when the AS model has no strand force increment (0 kN) but RS model has, then at this situation the error is infinite. The column restraining force also has large error, because the AS and RS model have different calculation on column restraining force. But the error is not especially significant for the beam axial force, because the column restraining force is small of the large error floor. Even though the strand force incerement and column restraining force has large error, but this large error is small force the beam axial force, the largest error is only 23% at the 12-story frame lower floor. Neglecting the inherent error between the two models, then using the MPA on the PT-frame. At displacement (3 and 6-story frame has 5% error, 12-story frame has 10% error) and interstory drift (3 and 6-story frame has 10% error, 12-story frame has 20% error). Althogh the strand force increment (3-story frame has 40% error, 6-story frame has 30% error, 12-story frame has 65% error ) and the column restraining force has large error, but this error for the beam axial force is small (3, 6-story frame has 10% error, 12-story frame has 20% error).