lengthen the bottom portion of the beam. This
part is said to be in tension, and that is where the
steel reinforcing bars are needed. As a result of
the combination of the concrete and steel, the
tensile strength in the beam resists the force of
the load and keeps the beam from breaking apart.
At the exact center of the beam, between the
compressive stress and the tensile stress, there is
no stress at all—it is neutral.
In the case of a continuous beam, it is a little
different. The top of the beam may be in
compression along part of its length and in
tension along another part. This is because a
continuous beam rests on more than two supports.
Thus, the bending of the beam is NOT all in one
direction but is reversed as it goes over
intermediate supports.
To help the concrete resist these stresses,
engineers design the bends of reinforcing steel so
that the steel will set into the concrete just where
the tensile stresses take place. That is why some
reinforcing rods are bent in almost a zigzag
pattern. The joining of each bar with the next,
the anchoring of the bar ends with concrete, and
the anchoring by overlapping two bar ends
together are some of the important ways to
increase and keep bond strength. Some of the
bends you will encounter are shown in figure 7-11.
Figure 7-11.-Typical reinforcement bar bends.
7-8
