Chapter 10 - Reinforced Beams

Flexure formula do not apply directly to composite beams because it was based on the assumption that the beam was homogeneous. It is therefore necessary to transform the composite material into equivalent homogeneous section. To do this, consider a steel and wood section to be firmly bolted together so that they can act as one unit. Shown below are the composite wood and steel section and the corresponding equivalent in wood and steel sections.



The quantity n is the ratio of the moduli of elasticity of stronger material to the weaker material. In the above case, n = Es / Ew.

031 Review Problem - Cost of mainline sewer pipe

Problem 31
One section of the mainline sewer pipe for the city of Annapolis passes through a tunnel 484 ft. long. The cross section of the tunnel is shown in the figure. The sewer pipe is 16 in. in external diameter and is partially embedded, in a mattress of concrete, a cross section of which is shown in the figure. Find the total cost (a) of digging the tunnel at $5.00 per cubic yard, (b) of pouring of concrete at $9.00 per cubic yard.



030 Review Problem - Amount of molten glass in a lump

Problem 30
Window glass formerly was made by gathering a lump of molten glass on the end of a hollow rod and blowing it into the form of large hollow cylinder about 6 ft. long and 1-1/2 ft. in diameter. This was cut longitudinally and then placed in an oven and heated until it softened, when it was flattened out into plates and cut into desired sizes. If this plate was 0.12 in. thick, find the amount of glass in the original lump.