Reinforcing Steel:
Steel is the best material for reinforcing concrete because the
coefficients of expansion of the steel and the concrete are considered
almost the same; that is, at a normal temperature, they will expand
and contract at an almost equal rate. (At very high temperatures,
steel will expand more rapidly than the concrete, and the two
materials will separate.)
Steel also works well as a reinforcement for concrete because
it makes a good bond with the concrete. This bond strength is
proportional to the contact area surface of the steel to the concrete.
In other words, the greater the surface of steel exposed to the
adherence of the concrete, the stronger the bond.
Figure 7- 10. - Types of deformed reinforcing
bars:
A deformed reinforcing bar is better than a plain round or square
one. In fact, when plain bars of a given diameter are used instead
of deformed bars, approximately 40 percent more plain bars must
be used.
The adherence of the concrete depends on the roughness of the
steel surface: the rougher the steel, the better the adherence.
Thus, steel with alight, firm layer of rust is superior to clean
steel, but steel with loose or scaly rust is inferior. Loose or
scaly rust may be removed from the steel by rubbing the steel
with burlap. The requirements for reinforcing steel are that it
be strong in tension and, at the same time, ductile enough to
be shaped or bent cold.
Reinforcing steel may be used in the form of bars or rods that
are either PLAIN or DEFORMED or in the form of expanded metal,
wire, wire fabric, or sheet metal. Each type is useful for a different
purpose, and engineers design structures with these purposes in
mind.
Plain reinforcing bars are usually round in cross section. They
are used as main tension reinforcement for concrete structures.
They are the least used of the rod type of reinforcement because
they offer only smooth, even surfaces for the adherence of concrete.
Reinforcing bars or rods are commonly referred to as rebar.
Deformed bars are like the plain bars except that they have either
indentations in them or ridges on them, or both, in a regular
pattern. The twisted bar, for example, is made by twisting a plain
square bar cold. The spiral ridges along the surface of the deformed
bar increase its bond strength with concrete. Other forms used
are the round- and square-corrugate d bars. These bars are formed
with projections around the surface that extend into the surrounding
concrete and prevent slippage. Another type is formed with longitudinal
fins projecting from the surface to prevent twisting. Figure 7-10
shows a few of the various types of deformed bars available. In
the United States, deformed bars are used almost exclusively,
while in Europe, both deformed and plain bars are used.
There are 11 standard sizes of reinforcing bars. Table 7-1 lists
the bar numbers, weight, and nominal diameters of the 11 standard
sizes. Bars No. 3 through No. 18, inclusive, are deformed bars.
Remember that bar numbers are based on the nearest number of 1/8
in. (3. 175 mm) included in the nominal diameter of the bar. To
measure rebar, you must measure across the round square portion
where there is no deformation.
Table 7-1. - Standard Reinforcing Bars
The raised portion of the deformation is not considered in measuring
the rebar diameter
| Bar
Numbers |
Weight |
Nominal
Diameter |
| Pounds
Per Foot |
Inches |
Millimeters |
| #3 |
0.376 |
0.375 |
9.5 |
| #4 |
0.668 |
0.500 |
12.7 |
| #5 |
1.043 |
0.625 |
15.8 |
| #6 |
1.502 |
0.750 |
19.0 |
| #7 |
2.044 |
0.875 |
22.2 |
| #8 |
2.670 |
1.000 |
25.4 |
| #9 |
3.400 |
1.129 |
28.5 |
| #10 |
4.303 |
1.270 |
31.7 |
| #11 |
5.313 |
1.410 |
35.9 |
| #14 |
7.650 |
1.693 |
43.0 |
| #18 |
13.600 |
2.257 |
57.3 |
