箱型柱內EGW或ESW銲道背襯板固有裂縫問題之分析與改善

Analysis and Improvement for the Inherent Backing-bar Crack Problem of Electrogas and Electroslag Welding in Box-Columns

林容暄(Rong-Shiuan Lin) ； 鍾興陽(Hsin-Yang Chung) ； 林明勳(Ming-Hsun Lin)

《中國土木水利工程學刊》 24卷2期 (2012/06) Pp. 169-183

https://doi.org/10.6652/JoCICHE.201206_24(2).0007

摘要

國內鋼結構建築所採用的箱型柱，常採用電熱熔渣（Electroslag Welding，ESW）或電熱氣體電弧銲接（Electrogas Welding，EGW）在箱型柱內部接合柱板與內橫隔板，此兩種銲接方法在銲接時須使用背襯板以防止末凝固的熔融銲液流出，當銲液凝固形成銲道後，會有背襯板與柱板的接觸面形成所謂的「固有裂縫」，而箱型柱內的此種固有裂縫在大地震作用下有開裂並造成EGW或ESW銲道斷裂之虞，本研究由基本破壞力學的觀點出發，以應力強度因子做為衡量固有裂縫尖端應力集中程度的指標，對EGW或ESW銲道背襯板的固有裂縫問題，以有限元素法配合最小乘法進行詳細的己和參數分析，並對可能造成EGW或ESW銲道破外之四種施工問題進行數值分析與討論，本研究特別針對EGW或ESW銲道背襯板之固有裂縫所造成的問題，測試「削角式背襯板」的改良方法，經過數值分析證實此種方法確實可以明顯降低固有裂縫尖端的應力強度因子，減低裂縫開裂的風險，此外，本研究製作了一支包含「柱板－內橫隔板EGE銲」和「柱板－梁翼板全滲透銲」的梁柱十字接頭試體，並對此試體進行非接觸式的光學實驗，來實際量測試體上的三條背襯板固有裂縫再填角銲補強前與補強後的應力強度因子變化，透過實驗與數值分析結果的比較，證實所採用之數值分析方法之正確性。

關鍵字

電熱氣體電弧銲接 ； 電熱熔渣銲接 ； 應力強度因子 ； 數位影像相關法

並列摘要

Electroslag welding (ESW) and electrogas welding (EGW) are frequently used for joining column plate and diaphragm plate in the box-column construction in Taiwan. These two welding methods utilize backing bars to prevent molten weld metal from leaking out. When the molten weld metal solidifies, an ”inherent crack” forms between the backing bar and the column plate. When a large-scale earthquake strikes, this kind of inherent cracks might propagate and result in fractures of the EGW or ESW joints. Applying basic fracture mechanics, this study took stress intensity factor as the index for measuring the stress concentration of an inherent backing-bar crack tip. For the inherent backing-bar crack problem in EGW and ESW, the detailed geometric parameter analysis was performed by using finite-element method and least-squares method. The four construction problems which might cause fractures in EGW and ESW joints were analyzed and discussed. An improved method using ”corner-cut” backing bars in EGW and ESW was tested in this study. The numerical analysis verified that the improved method could effectively lower the stress intensity factor of the inherent backing-bar crack tip and reduce the risk of crack fracturing. In addition, a non-contact optical experiment was conducted in this study to measure the stress intensity factor variations of the three inherent backing-bar cracks in a cruciform specimen before and after the fillet weld reinforcement. After comparison, the experimental results verified the accuracy of the numerical analysis method utilized in this study.

並列關鍵字

electrogas welding ； electroslag welding ； stress intensity factor ； digital image correlation