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| OPEN TREAD STAIR TREAD |
| A standard staircase thread manufactured from a form of expanded metal or welded wide mesh. (Open mesh walkway.) |
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| OPEN WEB GIRDER |
| Triangulated girder similar to an N or warren girder. |
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| OUTSTAND |
| The distance from the centre line of web or back of angle to the edge of the unstiffened flange or leg. |
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| OVERHEAD CRANE |
| Traveling crane mounted on crane beams supported above ground by a structural framework or gantry structure. |
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| OVERTURNING |
| The result of the action of applied forces, tending to produce a rotation about a point on the base. |