高等韌性與中等韌性箱型鋼柱寬厚比發展及AISC 341設計建議

Abstract

本研究延續Chou and Wu (2019)，Chou and Chen (2020)與Chou et al. (2024) 之研究，探討銲接箱型柱在中高軸力下的耐震行為。Chou and Wu (2019)研究了混凝土充填箱型柱輿空心箱型柱之耐震行為。其中空心箱型柱之寬厚比為18與20， 軸力比皆0.4 Pya。Chou and Chen (2020) 研究了單箱型鋼柱的試驗（共六組），涵蓋不同的寬厚比、軸力比以及不同的載重歷史（標準反覆載重與近斷層載重，參見Lin and Chou (2022)）。研究的寬厚比範圍為11, 12, 14, 16, 及20，其中三組試體滿足AISC 341-16規範的λhd限制。試驗結果顯示，AISC 341之載重歷時(Cyclic)比近斷層載重更為嚴格。Chou et al. (2024)研究了箱型鋼柱在一層樓子構架中的耐震行為，並與Chou and Chen (2020)中相同寬厚比和軸力比的單柱試驗（兩端為固接端）進行了比較，探討了邊界條件對柱構件耐震能力的影響。結果顯示，一層樓子構架的試體均可達到0.04 rad的最大側位移角。例如，單柱試驗I-16-40僅達到0.03 rad的最大側位移角，而一層樓子構架試驗S-16-40達到了0.04 rad。從試驗結果來看，AISC 341-22目前的箱型柱塑性設計寬厚比限制（λhd）相較於台灣鋼結構規範（2010）限制以及日本建築學會(AIJ)規範限制顯得相當保守。本研究主要延續Chou and Chen (2020)的單柱研究，考慮更大的寬厚比範圍（24至36）。斷面分別為380x380x10 mm，380x380x13 mm及400x400x15 mm。每個試體在兩種不同的軸力（0.2和0.4 Pya）下進行試驗，共計六組試體。所有試體均使用SN490B鋼材（降伏強度345至419 MPa）製造，並進行4米高的全尺寸試驗。試驗結果將考慮不同載重歷史的影響以及邊界條件的影響，對箱型鋼柱的寬厚比（b/t ratio）限制進行研究，並為美國規範制定新的寬厚比建議。試驗成果顯示AISC 341-22的寬厚比限制目前為過於保守。為了進一步確認所提出的寬厚比建議，還進行了實尺寸三層樓振動台試驗。一樓抵抗側力構架為兩組相同的箱形鋼柱，b/t為27.4，初始軸力比皆為0.11 Pya，按照所提出的建議為高等韌性桿件。結果顯示，所建議的限制與試驗結果相當合理，并按照Ozkula et al. (2021) 的定義，可以達到0.037 rad的SDAcr，接近AISC規定的需求0.04 rad。

This research mainly extends the research by Chou and Wu (2019), Chou and Chen (2020), and Chou et al. (2024) and attempts to systematically organize gathered data into a proposed seismic compactness limit for a built-up box column. Chou and Wu (2019) tested six concrete-filled high-strength box column (CFBC) specimens and two built-up box columns under cyclic loading history. Chou and Chen (2020) tested six isolated built-up box column specimens; four were tested cyclically, and another two were tested under a near-fault loading protocol developed by Lin and Chou (2022). It suggests that the cyclic loading prescribed by AISC 341 is too stringent. Later, Chou and Chen (2024) attempts to study the effect of boundary condition, by testing a subassemblage with identical b/t ratio and axial load ratio in a study by Chou and Chen (2020). The study suggests that the current AISC 341 (2022) compactness limit for built-up box columns is too stringent. Based on the results, this study also attempted to develop a seismic compactness limit for built-up box columns. Extending Chou and Chen's (2020) study, a total of six full-scale built-up box columns (HBC) with three different b/t ratios, where all of them are considered as non-moderately ductile by the AISC 341 (2022), were tested. For each b/t ratio, the specimen was tested with two axial load ratios, respectively. Specimens were built with SN 490B steel with actual yield strength ranging from 345-419 MPa. All specimens were tested under cyclic loading with fixed-fixed boundary conditions under constant axial load. The built-up box columns were all 4 m in height, with widths ranging from 380-400 mm, b/t ratios ranging from 24-36, and axial load ratio varying between 0.2Pya and 0.4Pya. These test data were then compiled and analyzed using the multivariate regression method, considering significant parameters affecting the specimen's behavior. The effect of boundary condition and lateral loading sequence was also considered to develop the compactness limit. The result suggests that the current seismic compactness limit for the built-up box column can be relaxed, and adding an axial load ratio to the calculation will reduce an overly conservative limit. To further confirm the proposed limit, a shaking table test was also conducted. Two identical built-up box columns with a b/t ratio of 27.4 and an initial axial load ratio of 0.11 Pya which are considered as highly ductile members by the proposed limit, were part of the lateral force-resisting system of a full-scale three-story specimen. The test result suggests a good confirmation between the proposed limit and the test result, with the specimen reaching an SDAcr of 0.037 rad, close to 0.04 rad prescribed by AISC.