middle to the opposite side pull away from the middle.
This is similar to what happens inside the beam.
For instance, take a simple beam (a beam resting
freely on two supports near its ends). The dead load
(weight of the beam) causes the beam to bend or sag.
Now, from the center of the beam to the bottom, the
forces tend to stretch or lengthen the bottom portion
of the beam. This pad 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
Figure 7-4.Tension in steel bars.
Then, when it seems the bar will snap like a rubber
band it recovers strength (due to work hardening).
Additional pull is required (fig. 7-4, view C) to
produce additional stretch and final failure (known as
the ULTIMATE STRENGTH) at about 55,000 psi for
BENDING REINFORCING BARS
The job of bending reinforcing bars is interesting
if you understand why bending is necessary. There are
several masons. Let us go back to the reason for using
reinforcing steel in concretethe tensile strength and
compressive strength of concrete. You might compare
the hidden action within a beam from live and dead
loads to the breaking of a piece of wood with your
knee. You have seen how the splinters next to your
knee push toward the middle of the piece of wood
when you apply force, while the splinters from the
In the case of a continuous beam, it is a little
different. The top of the beam maybe 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. It is reversed as it goes over
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 the reason you may have to
bend some reinforcing rods in almost a zigzag pattern.
The joining of each bar with the next, the anchoring
of the bar ends within 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 be required to make in
reinforcing bars are shown in figure 7-5.
The drawings for a job provide all the information
necessary for cutting and bending reinforcing bars.
Reinforcing steel can be cut to size with shears or with
an oxygas cutting torch. The cutting torch can be used
in the field.
Before bending the reinforcing bars, you should
check and sort them at the jobsite. Only after you
check the bars can you be sure that you have all you
need for the job. Follow the construction drawings
when you sort the bars so that they will be in the proper
order to be bent and placed in the concrete forms. After
you have divided the different sizes into piles, label
each pile so that you and your crew can find them
For the job of bending, a number of types of
benders can be used. Stirrups and column ties are
normally less than No. 4 bar, and you can bend them