電熱熔渣銲儲倉口形狀對其破壞時機之影響

Effects of chamber geometry on electro-slag welding failure

10.6849/SE.202306_38(2).0001

楊鈞堯(Chun-Yao Yang)；蔡克銓(Keh-Chyuan Tsai)

鋼箱型柱 ； 梁柱接頭 ； 電熱熔渣銲 ； SM570M-CHW高強度鋼 ； 喇叭形儲倉口 ； 有限元素模型分析 ； 鋼材破壞預測模型 ； steel box column ； welded moment connection ； electro-slag welding ； SM570M-CHW steel ； flared chamber ； finite element model analysis ； steel fracture prediction model

結構工程

38卷2期（2023 / 06 / 01）

5 - 38

繁體中文;英文

鋼箱型柱為傳遞梁彎矩，常使用電熱熔渣銲（Electro-Slag Welding, ESW）在柱內配置橫隔板。因施工誤差或鋼柱兩向梁深不同，而致梁翼與橫隔的高程偏心，在銲道熱影響區（Heat Affected Zone, HAZ）旁的初始縫隙尖端易發生脆性破壞。將ESW熔填截面形狀（儲倉口）由矩形改為喇叭形，可增加熔幅但亦會提升ESW入熱量。本研究利用SM570M-CHW鋼材可容忍高入熱的特性，探討ESW耐震行為。為量化研究ESW破壞機制，現採用MM-CVGM鋼材破壞預測模型以預測ESW的破壞時機。先對過往曾有之2組ESW元件單向拉伸試驗及7組實尺寸梁柱接頭反覆載重試驗，分析顯示MM-CVGM預測所得與試驗相差不超過1個載重迴圈，相較舊用模型更準確且保守。本研究另再執行4組實尺寸梁柱接頭反覆載重試驗，探討儲倉口與梁翼偏心對ESW破壞之影響。當儲倉口由傳統矩形改為小或大喇叭形，試體由1.5%層間位移角可改善至4%才發生破壞。為有效預測大型構件受低週疲勞之破壞，本研究修改MM-CVGM模型的破壞判斷式，藉有限元素模型中首先破壞的元素與群組，決定整體破壞時機，將此應用於4組試體可得預測與試驗相差皆不超過1個載重迴圈。為探討母材及銲材的韌性差異，本研究另進行圓周刻痕試片之反覆拉伸試驗，再建立有限元素模型與代表性體積單元模型分析，結果顯示，不同來源的同系列鋼材，可獲得相似的破壞曲線且誤差在10%內。母材為SM570M-CHW時HAZ破壞曲線斜率為ESW之114%與CJP之88%，三者有相同的破壞臨界值且差異在5%內；母材改為SN490C時HAZ的破壞臨界值即降至29%。本研究建議柱板若為SN490C或SM570M-CHW，皆可採用喇叭形儲倉口，以有效延緩ESW之脆性破壞。

In order to transfer the steel beam moment, diaphragm plates are welded inside the box column at the beam flange elevations. Electro-slag welding (ESW) is commonly used to attach the diaphragms to the column. Due to the fabrication imperfection or the frame beam depth difference, eccentricity between beam flange and diaphragm elevations may exist. This situation could lead to brittle fracture initiated at the tip of initial slit near heat affected zone (HAZ). By changing the ESW chamber from a rectangular to a flared cross section, the fusion zone can be increased, but with a price of increasing the thermal input. Considering its advantage of high heat tolerance, SM570M-CHW high strength steel column is considered. This study firstly applied the MM-CVGM fracture prediction model to the tests of two ESW component specimens and seven full-scaled steel beam-to-box column (BC) subassembly specimens conducted in previous studies. Analytical results indicate that the difference between MM-CVGM prediction and test results is no more than one loading cycle, which is more accurate and conservative than the previous model. Additionally, four full-scale BC specimens were fabricated and tested to investigate the effects of chamber geometry and column flange thickness on ESW performance. Results show that the joint with a rectangular ESW failed at the 1.5% inter-story drift ratio (IDR) cycle, while the fractures were delayed until the 4% IDR when the ESW sections were changed to a large or small flared shape. The fracture criterion of the MM-CVGM model was modified in this study. The overall failure initiation is determined by the difference of the first crack initiation between the element and the group. Applying this conditional fracture criterion to the test results, the difference between the prediction and test results is no more than one loading cycle. Circumferential-notched tensile coupon tests were conducted to investigate the ductility difference between the base and weld metals. This study utilized representative volume element models in finite element model analyses. Results show that even the steels are from different sources, very similar failure response can be observed for the same grade of steel with a difference less than 10%. Analytical results indicate that the slope of damage evolution curve of HAZ in the SM570M-CHW base metal is 114% of ESW zone and 88% of CJP zone. Three regions have the same critical damage threshold and the difference is within 5%. When the base metal is changed to SN490C, the critical damage threshold of HAZ is reduced to 29%. Based on the research results, it is recommended that the ESW chamber be considered with a flared section when grade SM570M-CHW or SN490C steel is selected for the column in order to effectively delay the ESW crack initiation.

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