H型鋼柱耐震行為: 兩層樓子構架與固接柱之試驗

Abstract

本研究探討H型鋼柱(H Shape Column)於不同邊界條件下(Fixed-Flexible、Fixed-Fixed)之耐震行為，主要試驗參數包括邊界條件及寬厚比，共計有五組試體。H型鋼柱斷面變換了腹板寬厚比分別為37與49，且皆滿足AISC 341-16高韌性構件（Highly Ductile Members）之寬厚比規定。試體類型分別為兩層樓子構架試體(Fixed-Flexible)與單柱試體(Fixed-Fixed)，並使用SN490B系列鋼材(標稱降伏強度325~445 MPa)，以固定軸力下(20%Py)進行AISC 341 (2016)標準反覆載重歷時試驗。試驗結果顯示本研究Fixed-Flexible邊界條件其塑性行為略優於Fixed-Fixed邊界條件；並發現即使真實抗彎構架系統滿足美國鋼結構建築耐震規範AISC 341-16對於強柱弱梁的規定，柱依然有產生塑鉸的風險。 本研究將試驗結果與NIST (2017)、ASCE 41(2013 2017)及Ozkula et al.(2017c) 所提出之背骨曲線進行比較，發現各規範背骨曲線皆無法反應真實的彈性勁度 ，因此提出建議的修正公式進行修正。而對於Fixed-Fixed邊界條件之試體，彈性勁度 又以NIST(2017)與ASCE 41(2017)預測最為準確；對於最大彎矩及最大轉角又以NIST(2017)預測最為準確。

The effects of boundary conditions and local web slenderness ratios on the H-shaped steel columns (HC) hysteretic behavior were experimentally investigated. This study discusses the findings from 5 half-scale steel column tests subjected to the AISC specified cyclic loading and constant axial load (20% Py). The specimens with local web slenderness ratios 37 and 49 satisfied AISC 341 requirements for highly or moderately ductile elements. To reflect realistic boundary conditions, two-story steel subassemblage frames with a single column and steel beams at two floors were tested to evaluate the cyclic behavior of steel columns, and compared with double-curvature member testing afterwards. Although the test results specify the influence of boundary conditions on the damage progression of steel columns, there is not much difference in the ductility of specimens with different boundary conditions. Moreover, the tests reveal that the column in moment-resisting frame has high risk of yielding even if it satisfies AISC 341 strong-column weak-beam requirements. This study compares the test results with the backbone curves proposed by NIST (2017), ASCE 41 (2013 2017) and Ozkula et al. (2017c). It shows that the backbone curves proposed by each study will overestimate the elastic stiffness due to the different type of boundary conditions. To address these issues, the modified elastic stiffness was proposed. For the specimens with Fixed-Fixed boundary conditions, the NIST (2017) and ASCE 41 (2017) predictions of the elastic stiffness are the most accurate. Furthermore, the NIST (2017) predictions are plenty accurate for the maximum flexural strength and the maximum rotation.