SM570M-CHW高強度鋼箱型柱翼厚與梁翼板高程偏心對電熱熔渣銲破壞效應

Effects of SM570M-CHW steel beam flange eccentricity and box-column flange thickness on electro-slag welding failure

黃昱竣(Yu-Jun Huang) ； 胡祐瑋(You-Wei Hu) ； 覃志光(Chih-Kuang Chin) ； 蔡青宜(Ching-Yi Tsai) ； 李昭賢(Chao-Hsien Li) ； 莊勝智(Sheng-Jhih Jhuang) ； 林克強(Ker-Chun Lin) ； 蔡克銓(Keh-Chyuan Tsai)

《結構工程》 35卷3期 (2020/09) Pp. 5-38

https://doi.org/10.6849/SE.202009_35(3).0001

摘要

箱型柱具雙強軸特性，在台灣鋼結構中應用普遍，為將梁彎矩傳入柱構件，箱型柱中與梁翼相對應之高程須置入內橫隔板，內橫隔板與箱型柱之銲接工法通常採用電熱熔渣銲（Electro-Slag Welding, ESW），而為減少柱斷面積，高強度SM570M-CHW鋼的應用也漸普及。本研究利用高強度鋼材探討箱型柱中ESW的耐震行為，並採用既有的鋼材破壞預測模型探討ESW是否會破裂與破裂時機。本研究以11組ESW元件單向拉伸試驗與4組實尺寸梁柱接頭反覆載重試驗探討柱翼板厚度與梁翼板偏心對於ESW破壞的效應，試驗結果顯示ESW元件僅受單向拉力作用時，只要「梁翼橫隔交疊高度」小於等於零，且偏心大於一倍柱翼板厚度，ESW就會發生破壞；但「梁翼橫隔交疊高度」大於或等於1/4梁翼厚時，偏心超過一倍柱翼板厚度仍不會於ESW發生破壞。實尺寸梁柱接頭反覆載重試驗中則證明當柱翼板厚度由25mm提升至45mm時，ESW由原先3%層間位移角發生破壞改善至層間位移角達5%尚未發生破壞。為探討ESW元件能否有效模擬梁柱接頭中的ESW銲道受力行為，本研究亦建立圓周刻痕試棒有限元素模型獲得材料參數之後，再進行ESW元件有限元素模型分析，並進行ESW關鍵區域破裂預測，結果顯示不論梁翼對ESW往梁腹方向亦或是反向偏心，有限元素模型皆能預測出ESW元件試體破壞時機且誤差小於12%；進而建立實尺寸梁柱接頭有限元素模型模擬接頭內ESW銲道在反覆載重作用下之受力行為，結果顯示當柱翼板厚度由25mm增厚至45mm時，應力集中現象明顯減緩，且尖端開口位移下降至原先1/3倍，並可準確預測梁柱接頭內ESW破壞時機。本研究亦以柱翼板厚度、梁翼板厚度及橫隔梁翼交疊高度為參數進行研究，探討不同參數配置對ESW銲道關鍵區域破壞時機之影響。分析結果顯示，當柱翼板厚度與橫隔梁翼交疊高度提升，以及梁翼板厚度減少時，可降低ESW開裂之機會。本研究建議柱翼板厚度宜大於或等於橫隔板厚度，且橫隔梁翼交疊高度不宜低於四分之一倍之橫隔板厚度，以避免ESW之脆性破壞。

關鍵字

鋼箱型柱 ； 鋼梁柱接頭 ； SM570M-CHW鋼 ； 電熱熔渣銲 ； 圓周刻痕拉伸試驗 ； 鋼材破裂預測模型 ； 有限元素模型分析 ； 橫隔梁翼交疊高度

並列摘要

Steel box columns are widely used in seismic steel building structures in Taiwan. In order to effectively transfer the beam-end moment to the column, diaphragm plates are welded inside the box column at the same elevations of the welded beam flanges. Electro-slag welding (ESW) procedure is common applied to attach the diaphragm plates to the column. Recently, the SM570M-CHW grade high strength steel is prevailingas it reduces the column sizes. In this study, four full-scaled welded SM570M-CHW steel beam-to-column (BC)joint specimens and eleven ESW component specimens were fabricated and tested. The key design parameters of these specimens include column flange thickness, beam flange eccentricity with respect to the diaphragm plate. This study investigates the applicability of stress modified critical strain and degraded significant plastic strain modelsin predicting the crack initiation fracture of the diaphragm-to-column ESW joint. The ESW component specimens were subjected to monotonic tensile loads, while the welded BC joint specimenswere subjected to cyclically increasing displacement to investigate the effects of beam flange eccentricity and column flange thickness on the ESW fractures. Test results show that when the ESW was subjected to monotonic tension only, it could fracture when the ＂overlapping distance of beam flange and diaphragm＂ (OD) was smaller or equal to zero. On the contrary, it remained intact even when the ODwas greater or equal to thickness of beam flange. Cyclic test results of the welded BC joints show that the connection with the 25mm thick column flange failed at the 3% inter-story drift (IDR) cycle, while the specimen with the 45mm column flange went through 5% IDR cycle without failure. The finite element model analysisresults show that when the column flange thickness increases from 25mm to 45mm, the stress concentrations are reduced and the crack tip opening displacement is decreased by 3 times. This study also carried out parametric study, focusing on the effects of the column flange thickness, the beam flange thickness and the OD on ESW fracture. Results show that increasing the column flange thickness, or the OD and decreasing the beam flange thickness reduce the stress concentration near ESW. In order to avoid the ESW fracture, the results of this study suggest that column flange thickness be equal to or larger than diaphragm or beam flange thickness; and the ODbe larger than one quarter of the diaphragm or beam flange thickness.

並列關鍵字

steel box column ； SM570M-CHW steel ； electro-slag welding ； circumferentially notched tensile test ； steel fracture prediction model ； finite element analysis ； overlapping distance of beam flange and diaphragm