| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an iron lid for an underground structure, obtaining a coefficient of friction equal to that of an asphalt road surface even after abrasion of a projection as well as before abrasion, and obtaining a fixed frictional resistance regardless of an advancing direction of a tire to the iron lid. Ž<P>SOLUTION: A plurality of anti-skid projection groups 2 for a vehicle tire are formed at spaces on a reference surface S of the iron lid body 1, and the projection groups 2 are formed of a pair of projections 3 disposed close to each other. Each of the projections 3 includes a main projection 4 for the projection group and doublestage small projections 5A, 5B for the projection group formed like a stair on the top face of the main projection 4 for the projection group, wherein the top face of the uppermost stage small projection 5B for the projection group has a shape staying in a circle with a diameter of 25-35 mm, and the space between the outer peripheral surfaces of the adjacent projection groups 2 ranges from 10-40 mm. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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