高強度鋼梁翼板偏心與柱翼板厚度對電熱熔渣焊破壞效應

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

胡祐瑋(You-Wei Hu)

指導教授 ： 蔡克銓

國立臺灣大學/工學院/土木工程學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201802146

摘要

箱型柱因其雙強軸特性，在台灣鋼結構中應用非常普遍，為了將梁端彎矩順利傳入柱構件，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焊接工法通常採用電熱熔渣焊(electro-slag welding, ESW) 。而為了解決柱構件斷面過大的問題，高強度鋼材SM570M-CHW的應用也日漸普及。本研究利用SM570M-CHW高強度鋼材，探討箱型柱中電熱熔渣焊受梁翼與橫隔板高程偏心及柱翼相對厚度效應下的耐震行為，並採用Kanvinde與Deierlein在2004年提出的破壞預測模型(α Model與α Cyclic) ，採相同梁翼厚但以不同「柱翼板厚度」與「梁翼板偏心」作為主要研究參數，探討ESW是否可能破裂以及破裂時機。
本研究進行三組ESW元件單向拉伸試驗與兩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:若僅受36mm厚梁翼單向拉力作用，ESW能夠在偏心量超過一倍柱翼板厚度25mm的情況下達到27mm，仍未於ESW處發生破裂，此結果與過往研究結論偏心量不能超過一倍柱翼板厚度不同，主因為本研究內橫隔板厚36mm較以往研究厚，使ESW熔幅範圍增大進而提升耐震性能。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。
為使用破壞預測模型，本研究利用有限元素軟體ABAQUS進行有限元素模型分析，建立ESW元件與圓周刻痕試棒(CNT)分析模型獲得α Model材料參數α並進行ESW破裂預測，結果顯示ESW周圍關鍵元素皆不會發生破裂，與真實實驗情況一致。亦建立實尺寸梁柱接頭有限元素分析模型，觀測關鍵區域應力集中現象與尖端開口位移，並配合α Cyclic破壞預測模型討論反覆載重作用下ESW破壞時機，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約1/3倍，α Cyclic亦顯示以SN490材料參數能夠預測出與試驗結果相近的破裂時機。

關鍵字

鋼箱型柱 ； 鋼梁柱接頭 ； 電熱熔渣焊 ； SM570M-CHW高強度鋼材 ； 有限元素模型 ； 鋼材破裂預測模型 ； 圓周刻痕拉伸試驗

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, SM570M-CHW grade high strength steel is also widely adopted in steel building structure in order to reduce the member sizes. In this study, two full-scaled welded SM570M-CHW steel beam-to-column moment connection specimens and three 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 stress (SMCS) and Degraded Significant Plastic Strain models (DSPS) in 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 beam-to-column connection specimens were subjected to cyclically increasing displacement in order 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 remained intact even when the beam flange 27mm eccentricity was greater than the column flange thickness 25mm. This result is inconsistent with the findings from a former research, which suggested that the beam flange eccentricity should not be larger than the column flange thickness. This should be attributed to that a 36mm thicker diaphragm plate than the 25mm column flange has provided enough chamber for a large ESW fusion zone to develop. Thus, it has allowed the connection to sustain the 27mm beam flange eccentricity. Cyclic tests results of the welded beam-to-column moment connections showed that the connection with the 25mm column flange failed at the 3% IDR cycle, while the specimen with the 45mm column flange went through 5% IDR cycle without failure.
In order to compute the material parameter, α in the SMCS models, this study constructed finite element analysis (FEA) models to analyze the responses of ESW components and the circumferential notched test (CNT) specimens made from the ESW components. The FEA results confirm that all of key elements in the heat affected zone surrounding the ESW would not fail, which is consistent with the test results. This study also conducted the FEA on the welded beam–to-column moment connection models. The DSPS model parameter of SN490B steel computed in a previous research was adopted. The effects of column flange thickness on the EWS stress concentration and crack tip opening displacement (CTOD) under the cyclic loading are investigated. The FEA results show that when the column flange thickness increases from 25mm to 45mm, the stress concentrations are reduced and CTOD is decreased by 3 times. The comparison between the test and FEA results suggest that the DSPS model incorporated with the material toughness parameters obtained from SN490B steel can satisfactorily predict the fracture responses of the ESW diaphragm-to-column joint.

並列關鍵字

steel box column ； steel beam-to-column connection ； electro-slag welding ； SM570M-CHW high strength steel ； finite element model ； steel fracture predict model ； circumferentially notched tensile test

參考文獻

1. AISC (2005), “Seismic Provisions for Structural Steel Buildings,” American Institute of Steel Construction.

2. AISC (2005), “Specification for Structural Steel Buildings,” American Institute of Steel Construction.

3. American Welding Society (1992), D1.1-1992, Structural Welding Code.

4. A.M. Kanvinde, and G.G. Deierlein (2006), “Void Growth Model and Stress Modified Critical Strain Model to Predict Ductile Fracture in Structural Steels.” Journal of Engineering Mechanics, ASCE/June 2006/1907.

5. A.M. Kanvinde, and G.G. Deierlein (2007), “Cyclic Void Growth Model to Assess Ductile Fracture Initiation in Structural Steels due to Ultra Low Cycle Fatigue.” Journal of Engineering Mechanics, ASCE/June 2007/701.