افغانستان
Kabul, afghanistan 2019 کابل افغانستا کابل افغانستان
Different types of timber support
Different types of timber supports Timber props Timber placed normally between the roof and floor of roadways, etc. in coal mines is called timber prop. Timber prop in metal mines is sometimes called stull. A timber prop when erected in a mine to support the roof should yield slightly under the roof weight. The timber prop is strongest when the load acts parallel to its length; a prop as such is almost unyielding but a certain yield is obtained by; a) tapering it at the foot or top, or b) and providing a lid at the top as a compressible cushion between the roof and the end of the prop. In flat seams the prop is erected vertical, and in inclined seams, axis of the prop should be normal to the dip of the seam. The prop then offers the maximum resistance to the roof. A prop which is so set that its axis is between the vertical and the normal to the seam is known as and underset prop. Erection of underset props is not common as it is not possible for the timberman to judge wh
