- 期刊
箱型鋼柱於不同寬厚比軸力及近斷層地震下的耐震行為與背骨曲線發展
Seismic Performance and Backbone Curve Development of Steel Box Columns Considering Compactness Ratios, Axial Loads and Near-Fault Motions
摘要
本研究藉由分析7層樓挫屈束制斜撐構架受遠域及近斷層地震之反應，發展一樓鋼柱的遠域及近斷層側向載重位移歷時，並以實驗方式探討高強度銲接箱型鋼柱受遠域及近斷層載重作用下之耐震行為。自國內外地震中選取11組近斷層和11組遠域地震歷時紀錄，調整至最大考量地震（MCE）等級進行非線性歷時分析，發展一樓鋼柱受近斷層地震之側向載重歷時，含有自-2%到4%側位移角的位移脈衝，及2.5%的殘餘側位移角，藉此探討臺灣高強度鋼柱於中、高軸力下之耐震行為。試驗參數包括柱寬厚比、軸力比及近斷層載重歷時，共規劃6組使用SM570MC鋼材製造之全尺寸銲接箱型鋼柱試體，寬厚比介於11～21。試驗顯示寬厚比較小之銲接箱型鋼柱可有效減緩鋼板局部挫屈；美國AISC 341（2016）之高韌性構件寬厚比限制為12.9（以標稱降伏強度Fyn=420 MPa及材料超強因子係數Ry=1.2為例），而臺灣鋼結構極限設計規範（2010）對全滲透銲接箱型鋼柱之寬厚比放寬至21，兩者差異極大，較寬鬆的鋼柱寬厚比無法確保在承擔中高軸壓力下的鋼柱在大位移下（側位移角＞3%）的耐震行為，在高耐震區使用銲接箱型鋼柱承擔中高軸壓力（25～40%Py），建議應採用美國AISC 341（2016）之高韌性柱構件進行設計。本研究並藉由搜集以往的實驗資料發展鋼柱的側向位移背骨曲線，預測鋼柱的側力與側位移行為，大幅改善ASCE 41（2013）及NIST（2017）對箱型鋼柱背骨曲線預測在高軸力下過度保守及低軸力下不保守的情形。
並列摘要
This paper presents the seismic evaluation of high-strength steel columns in a seven-story buckling-restrained braced frame under two sets of 11 far-field motions and 11 near-fault motions, representative of maximum considered earthquake (MCE) level. The proposed near-fault displacement protocol contains a large displacement pulse from -2% to +4% drift with several small displacement cycles and a residual drift of 2.5%.The AISC 341 (2016) has a more stringent width-to-thickness (b/t) limit for highly ductile hollow box columns (HBCs) than the AIJ (2010) or Taiwan Code (2010), resulting in significant thickness difference in design. For example, the b/t limits for a highly ductile box column member with a nominal yield strength, Fyn=420 MPa, and an over-strength factor, Ry=1.2, are 12.9 and 21 based on AISC 341 (2016) and Taiwan Code (2010), respectively.Moreover, the cyclic backbone curves based on ASCE 41 (2013) and NIST (2017) underestimate the post-buckling flexural strength of HBCs, particularlyin high axial compression force.The authors conducted cyclic tests of six full-scale, built-up HBCs using SM 570M steel with the actual yield strength of 460-530 MPa using standard and proposed loading protocols.The gathered test data, supported by more test data in this work, are analyzed by a multiple regression method to obtain empirical formulations for the backbone curves of box columns that can predict the maximum column moment, plastic rotation and post-yield hardening stiffness. The proposed formulation reasonably predicts the first-cycle envelope curves of built-up HBCs, significantly improving prediction results based on both ASCE 41 (2013) and NIST (2017).