Home >> Cyclopedia-of-architecture-carpentry-and-building-a-general-reference-v-05 >> 000 For Railway Bridges to Standard Connections >> Note_2

NOTE. In all above cases, partitions are of 3-inch terra cotta blocks, and come only over girders. Clear story height = 10 feet. Give loads for both beams and girders.

8. Required a lintel over opening shown by Fig. 92. Clear span 15 feet, wall 16 inches thick and 50 feet high. No floor or any load carried by wall.

In this type of opening, the narrow piers or columns under the lintels make it necessary to figure the full load of wall, as otherwise the narrow base supporting the heavy overhanging mass of masonry would cause at the piers a thrust that would necessitate continuous tie rods. The full load, there fore, would be 50 X 15 X 1.33 X 115 = 115,000 lbs. The effective span of lintel is 16 feet ; the capacity of two 18-inch 55-lb. I beams for this span is 117,800 lbs., and these would, therefore, be the required sections.

Required the size of lintel of type B, Fig. 91. Span between centers of bearings, 7 feet. Wall 20 inches thick. Floor load 200 lbs. per square foot. Columns spaced 15 feet from wall.

In this case the piers at side of opening are sufficiently heavy for us to consider the wall over opening as arching, as shown by dotted lines.

Floor load =200 X 7.5 X 7 10,500 lbs.

Wall load = 7 X 3.5. X 1.67 X 115 = 4,697 lbs.

The full floor load should be provided for. The wall load is not a uniformly distributed load, and moment should be calculated by assuming load between center and end of girder as acting the way from the center of the girder.

The moment in foot-pounds of wall load can be obtained also by the use of the formula where p is the weight of a square foot of the masonry 12 of the given thickness, and / the span.

If the allowable fibre strain is 16,000, this gives a necessary section modulus of 11.0.

Two 7-inch 0.75-lb. I beams have a total section modulus of 12.0, and would, therefore, be sufficient.