The subject of reinforced concrete is not within the province of this
bulletin, but as openings of various widths are required in the walls of
most farm structures, a general explanation is given of the reinforcement
of lintels or that portion of concrete immediately above an opening, such
as a floor or window.
A lintel is a beam, and when a beam bends the lower part is stretched or
pulled while the upper portion is compressed. Good concrete will stand
great pressure but is not capable of resisting any great pulling or
tensile stress. For this reason steel is used in the lower portion to
take care of the tensile or pulling force.
It will be found generally satisfactory, where no heavy or concentrated
load occurs over an opening and the span is not more than 4 feet, to
place two rods three-eighths of an inch in diameter in the bottom of the
lintel, so that there will be 1 inch of concrete below them. Two diagonal
rods should be placed at each top corner of a window or door, as shown
in Figure 18. When the opening is between 4 and 8 feet the rods should
be bent up as shown in Figure 19 and when between 8 and 12 feet, three
one-half inch rods should be used, two of them being bent.
Barbed wire, old fencing, and scrap or rusty iron is not suitable for
reinforcement. Loose rust should be cleaned off the rods and they should
be free of grease and oil.
[Illustration: Fig. 18.--Reinforcement of openings less than 4 feet wide.]
[Illustration: Fig. 19.--Reinforcement of openings more than 4 feet wide.]