. Economic Papers. h 22 CULVERTS AND SMALL BRIDGES FOR. COUNTRY ROADS IN NORTH CAROLINA 23 comes directly on the floor. Its durability is twice that of two inchflooring, although it costs only one-third more, since flooring must berenewed when worn to an inch thickness. Creosoted lumber is much more durable than ordinary timber andwill cost about $45 per 1,000 ft. B. M. in the eastern part of the State. Small Structures: Wood should never be used for any waterway wherea pipe can be used. The ordinary type of small timber culverts as constructed in mostsections of the State consists of a mudsil
. Economic Papers. h 22 CULVERTS AND SMALL BRIDGES FOR. COUNTRY ROADS IN NORTH CAROLINA 23 comes directly on the floor. Its durability is twice that of two inchflooring, although it costs only one-third more, since flooring must berenewed when worn to an inch thickness. Creosoted lumber is much more durable than ordinary timber andwill cost about $45 per 1,000 ft. B. M. in the eastern part of the State. Small Structures: Wood should never be used for any waterway wherea pipe can be used. The ordinary type of small timber culverts as constructed in mostsections of the State consists of a mudsill imbedded in an earth bankwith floor joists resting directly upon it. Most of the failures come fromundermining of the earth abutments or floating off of the entire struc-ture. A small culvert constructed as shown in Plate I should last until itrots out. The cost of a culvert of this type is approximately $35. Table III below shows the size and spacing of wooden floor joists forlonger span culverts. TABLE III—WOODEN BRIDGES (15 ROADWAY) Span No. of
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