| 摘要 |
PROBLEM TO BE SOLVED: To provide a sturdy and light-weight extensible ladder which does not bring useless material and eliminates swing when it is used. SOLUTION: In this extensible ladder 10, a lower ladder 11 using column members 15, 16, 38, 39, 55, 56 made of channels respectively, a middle ladder 12, and an upper ladder 13 are slidably connected to each other, and stoppers fixing these ladders at specified positions are provided. The web length of the column members 38, 39 of the middle ladder 12 are made longer than the web length of the column members 15, 16, 55, 56 of the lower ladder 11 and the upper ladder 13. Further, the section modulus of the middle ladder 12 is made larger than that of the lower ladder 11 and the upper ladder 13.
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