高強度鋼箱型柱之耐震試驗與背骨曲線發展

Abstract

本研究探討高強度鋼箱型柱於中、高軸力下之耐震行為，主要試驗參數包括寬厚比、軸力比、及載重歷時，共計有六組試體，箱型柱斷面寬度分別為360、290、400、315及385mm，寬厚比分別為20、16、14、12及11，其中有三組試體滿足美國AISC 341 (2016)規範之高韌性構件限制(λhd=12.9)皆施加40%Py的軸力，並使用不同載重歷時進行測試(AISC 341 (2016)之標準載重及近斷層載重歷時)；其餘三組滿足台灣規範(2010)之高韌性構件限制(λhd=21.7)，並變化不同的軸力比進行測試(25~40%Py)，皆使用AISC 341 (2016)之標準載重；試體製造皆使用高強度SM 570MC鋼材(降伏強度420~540 MPa)，以4公尺柱高進行實尺寸試驗，試驗內容為施加固定軸力並進行側向歷時加載。試驗結果顯示寬厚比較小之空心箱型鋼柱可達較大之側位移角且有效減緩鋼板局部挫屈問題；並發現台灣規範對全滲透銲接箱型鋼柱之寬厚比放寬至21，並不是適用於高軸力的柱子，若要作為耐震柱仍須採用美國AISC 341 (2016)規範之高韌性構件(λhd=12.9)進行設計；而載重歷時的比較結果，發現AISC 341 (2016)之標準載重較本研究所使用之近斷層載重歷時更為嚴格。 現行的設計規範美國AISC-LRFD(2016)、日本AIJ(2010)及台灣規範(2010)，對於鋼柱的彎矩強度預測仍較為保守，NIST (2017)及ASCE 41 (2013)之背骨曲線預測性雖比設計規範佳，但在高軸力(40%Py)下會能仍會低估鋼柱的強度及塑性轉角；而以本研究提出之背骨曲線公式，可較準確地預測鋼柱之最大強度及塑性轉角能力。

The seismic behavior of the high strength steel hollow box column (high strength HBC) under the high axial load was experimentally investigated. The parameters in this study included the width-to-thickness (b/t) ratio, axial load level and loading types. Full-size tests were carried out on six welded box-section columns fabricated from SM570MC (nominal yield strength 420 MPa~ 540 MPa). The HBC specimens were 290 to 400 mm in width and 4000 mm in height, with nominal b/t ratios varied from 11 to 21. The HBC specimens were tested under a constant axial load and the increasing cyclic loading (or near-fault loading). Experimental results indicate that smaller b/t ratio in HBC can delay the local buckling effectively, resulting in better ductility. Moreover, the width-thickness limit for HBC in Taiwanese specification, which is 21, can not apply to the cases under a high axial load. This means the smaller b/t requirement of highly ductile member (λhd=12.9) in AISC 341 (2016) should be used in the seismic design. Also, loading sequence for beam-to-column moment connections based on AISC 341 (2016) is stricter than the near-fault loading that we used in this work. All the design codes include AISC-LRFD(2016), AIJ(2010) and Taiwanese Code(2010) are conservative in predicting the flexural strength of high strength HBC. In this work, the backbone curve for hollow section steel column was proposed and compared with those proposed by ASCE 41 (2013) and NIST (2017). It shows that the backbone curves proposed by ASCE 41 (2013) and NIST (2017) will underestimate the flexural strength and the plastic rotation under a high axial load (40%Py). The backbone curve proposed by this work can give good accuracy in predicting the flexural strength and the plastic rotation of high strength HBC.