It is possible to set up the Roadside Barrier which is suitable for Performance Evaluation Criteria by domestic standard. But a number of section of expressway roadside have old guardrail that was installed before reform the guideline. These poor performance guardrails threaten driver s life. There is lots of difficult problem to change old guardrails that are installed 2,777km in expressway of whole road side at the same time. Especially budget problem. The purpose of study is to develop performance improvement guardrails by the minimum reinforcement. In this study, guardrail improvement method(SB1, 3, 5 grade) is developed through crash simulation using LS-DYNA 3D and vehicle crash test. And it's expected not only to decrease of collision accident but to increase safe level. Of course one thing that can t be missing is to reduce a lot of budget of guardrail change.

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Due to excellent weld quality, orbital welding with TIG is widely applied to pipe welding. But concave back bead is formed easily in overhead and inclined-up position of butt orbital welding. It is difficult to find a paper to overcome this problem. In this study, in order to make convex back bead in overhead and inclined-up position of pipe 5G welding, control method of molten pool was actively investigated. Melt run welds were conducted on thickness 4.0mm SS400 with overhead and inclined-up position and was observed the variation of bead shape after welding with the bead former developed. The height of back bead showed the trend of increase as the distance from molten pool to the bead former was decreased. Also, there is no trend in the bead width of front and back as welding position was changed or the distance from molten pool to the bead former was decreased.

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