| Summary: | 碩士 === 國立交通大學 === 土木工程系所 === 106 === In Taiwan, a box column that is composed of four plates is popularly used in steel building structures. Connections between the plates of box column and an internal diaphragm are T-joints and at least two T-joint connections are made by electro slag welds (ESW). Therefore, a corresponding Welding Procedure Specification (WPS) of the T-joint connection with ESW shall be made to get well materials, proper welding procedures and effective inspections. Up to now, a butt-joint connection WPS with EWS based on suggestions of AWS D1.1 and AWS A5.25 still widely used to be a verification procedure in most steel structure engineering in Taiwan. The butt-joint connection ignored the lamellar effects steel plate in out of plan direction is noted in this study. In addition, a cross-joint connection specimen that made by two ESWs is allowed in JASS 6 published AIJ to be the WPS of the ESW connection between box columns plate and diaphragm. Although, the Cross-joint connection can largely shorten the whole time of processing WPS, an issue of high heat input into the column plate by two ESWs is concerned here.
In this study, a steel of SM570 CHW is adopted and there are three types of specimen with ESW, including T-, butt- and cross- joint connection specimens, to be considered. Not only tensile test, Charpy V-notch (CVN) test and Vickers hardness test are conducted but also temperature measurement test, straight-beam ultrasonic test (UT) of detecting melted line between column plate and ESW are carried out, Test results of the CVN test show that most CVN values in the ESW and within head affected zone (HAZ) of base metal are less than 27 Joules at -5°C required in its material specifications, small portion even lower than 15 Joules. Supposing that CVN value should be more than (-5C) 15 Joules, the requirement of impact toughness might be insufficient for box column with greater demanding. Structural engineers shall carefully assess influences of the impact toughness to box column’s brittle fractures. Based on the results of measuring the melted line by straight-beam UT demonstrate that the accuracy significantly depends on size of testing probe. The smaller the probe, the better the accuracy. The probe of 10 mm diameter acquires the best accurate results for the melted line and the probe of 24 mm diameter, commonly used in Taiwan’s practices, obtains poor results. Based on deference of mechanical characteristics of steel plate in plane and out of plane, this research suggests that the WPS with ESW for the T-joint connection between box-column plate and internal diaphragm should not be replaced by the butt-joint connection.
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