1.PURPOSES AND TYPES OF REINFORCING STEEL
Reinforced concrete was designed on the principle that steel and concrete act together in resisting force. Concrete is strong in compression but weak in tension. The tensile strength is generally rated about 10 percent of the compression strength. For this reason, concrete works well for columns and posts that are compression members in a structure. But, when it is used for tension members, such as beams, girders, foundation walls, or floors, concrete must be reinforced to attain the necessary tension strength.
Reinforced concrete was designed on the principle that steel and concrete act together in resisting force. Concrete is strong in compression but weak in tension. The tensile strength is generally rated about 10 percent of the compression strength. For this reason, concrete works well for columns and posts that are compression members in a structure. But, when it is used for tension members, such as beams, girders, foundation walls, or floors, concrete must be reinforced to attain the necessary tension strength.
Steel is the best material for reinforcing concrete because the properties of
expansion for both steel and concrete are considered to be approximate] y the
same; that is, under normal conditions, they will expand and contract at an
almost equal rate
NOTE: At very high temperatures, steel expands more rapidly than concrete and
the two materials will separate.
Another reason steel works well as a reinforcement for concrete is because it
bonds well with concrete. This bond strength is proportional to the contact
surface of the steel to the concrete. In other words, the greater the surface of
steel exposed to the adherence of concrete, the stronger the bond. A deformed
reinforcing bar adheres better than a plain, round, or square one because it has
a greater bearing surface. In fact, when plain bars of the same diameter are
used instead of deformed bars, approximately 40 percent more bars must be used.
The rougher the surface of the steel, the better it adheres to concrete. Thus
steel with a light, firm layer of rust is superior to clean steel; however,
steel with loose or scaly rust is inferior. Loose or scaly rust can be removed
from the steel by rubbing the steel with burlap or similar material. This action
leaves only the firm layer of rust on the steel to adhere to the concrete.
NOTE: Reinforcing steel must be strong in tension and, at the same time, be
ductile enough to be shaped or bent cold.
