本研究將實尺寸箱型柱與H型梁之梁柱銲接接頭，加工製作成小型之梁柱接頭十字試體來進行火害後的拉力實驗。製作試體所選用的鋼材為SN490B，而十字試體主要由柱內隔板、箱型柱翼板及H型梁翼板三部份銲接製作組成；除了對照組試體（未熱處理試體）以外，其餘製作好的試體將放入高溫爐中加熱至900℃後，再分別以「空氣冷卻」及「水中冷卻」來模擬梁柱銲接接頭火害後之兩種冷卻情形，本研究針對「未熱處理」、「空氣冷卻」和「水中冷卻」三組試體，分別進行標準拉伸試驗、硬度試驗和拉力實驗，透過以上試驗瞭解梁柱銲接接頭受火害後，鋼材機械性質與破壞模式的變化，梁柱接頭十字試體（柱翼板= 25 mm）拉力實驗的部分結果顯示：有背墊板全滲透銲接試體中，空氣冷卻試體之最大拉力減少5%，韌性參數提升3%，水中冷卻試體之最大拉力提升17%，韌性參數減少87%；無背墊板全滲透銲接試體中，空氣冷卻試體之最大拉力減少5%，韌性參數減少1%，水中冷卻試體之最大拉力提升71%，韌性參數減少26%。試體的破壞模式顯示：空氣冷卻試體均在梁翼板端斷裂，與未熱處理試體破壞模式類似；水中冷卻試體因水冷淬火的關係且銲材的碳含量比鋼材少，因此銲道中所形成的麻田散鐵組織其硬度值較梁翼板與柱內隔板為低，也造成銲道之抗拉強度較梁翼板與柱內隔板低，所以造成水中冷卻試體容易在梁翼板與柱內隔板銲接之FCAW銲道處斷裂。

This study made small-scale tension specimens from full-scale steel beam-to-column welded joints to perform post-fire tensile experiments. All the specimens were made by SN490B steel. A specimen was composed of a column diaphragm plate, a box-column flange plate and a H-beam flange plate, and the three steel plates were connected by welding. Except for the control group specimens (without heat treatment), the other specimens were heated to 900℃ and then were cooled down by “air cooling” and “water cooling” to simulate the two cooling situations for beam-to-column welded joints after fire. The three groups of specimens (i.e., control group, air-cooling group and water-cooling group) were all tested by standard tensile test, hardness test and tensile experiment to investigate the material property and failure mode variations. The tensile experiment results of some small-scale tension specimens (column flange thickness=25mm) are as follows. In the CJP welded specimens with backing bars, the maximum load decreased 5% and the toughness parameter increased 3% for the air-cooling specimens. For the water-cooling specimens, the maximum load increased 17% and the toughness parameter decreased 87%. In the CJP welded specimens without backing bars, the maximum load decreased 5% and the toughness parameter decreased 1% for the air-cooling specimens. For the water-cooling specimens, the maximum load increased 71% and the toughness parameter decreased 26%. The failure modes of small-scale tension specimens showed that the air-cooling specimens all fractured at the beam flange plates, which were similar to the specimens without heat treatment. For the water-cooling specimens, due to the water quenching and the lower carbon content in weld metal, the hardness value of martensite formed in the weld pass was lower than those of beam flange and column diaphragm plates. The tensile strength of the weld pass was also lower than those of beam flange and column diaphragm plates. As a result, water-cooling specimens usually fractured at the FCAW weld pass between beam flange plate and column diaphragm plate.

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