1.1.2. Reinforcing Steel

Steel is also used as reinforcing bars in concrete, Table 16.2.

Reinforcing steel, commonly termed rebar or reinforcing bars, is an essential component in concrete structures. It serves to enhance the tensile strength of concrete, which is inherently strong in compression but weak under tension. Incorporating steel bars into concrete helps to absorb tensile forces and prevent cracking.

Think of concrete as a stretched rubber band. While a rubber band can withstand pulling forces (tension) to some extent, if pulled too hard, it will snap. By adding rebar (like weaving strong threads into the rubber band), the band becomes much more resistant to breaking under tension. This combination creates a stronger product.

Those bars have a deformation on their surface to increase the bond with concrete, and usually have a yield stress of 60 ksi.

Reinforcing bars typically feature surface deformations like ridges and grooves. These deformations enhance the mechanical bond between the steel and the concrete, ensuring that as the concrete shrinks or expands, the steel remains securely anchored within it. The yield stress of these bars, which is around 60 ksi, indicates the maximum stress they can withstand before deforming permanently.

Imagine trying to hold onto a smooth pole while climbing—a smooth surface makes it difficult to grip, causing you to slide down. However, if the pole has rough texture or ridges, it becomes easier to hold. This illustrates how the deformations on reinforcing bars help the concrete clutch onto the steel, ensuring stability and strength.

Stirrups which are used as vertical reinforcement to resist shear usually have a yield stress of only 40 ksi.

Stirrups are closed loops of rebar that are placed vertically within concrete beams or slabs to resist shear forces—forces that can cause the material to slide apart. They usually have a lower yield stress of about 40 ksi, as their primary role is to provide additional support against shearing rather than extending tensile capacity.

Consider a sandwich: if only the bread is present, it can easily fall apart with a sideways force. But if you add toothpicks (like stirrups) horizontally across the sandwich, it holds together more effectively. The stirrups function similarly, acting as supportive elements that keep the concrete intact under stress.

Bar Designation Diameter Area Perimeter Weight (in.) ( in2) (in) (lb/ft)

Reinforcing bars come in various sizes and specifications. The designation of a rebar includes its diameter, which affects its area and weight per foot. For example, a No. 5 bar has a diameter of 5/8 inch, a cross-sectional area of 0.31 in², and weighs approximately 1.043 lb/ft. Understanding these specifications helps engineers calculate how much rebar is needed for specific projects.

Think about selecting the right size of shoelace for your sneaker. A finer lace will not provide enough strength to keep your shoes tight if you're running, just as a thin bar may not be strong enough for heavy concrete flooring. Choosing the appropriate diameter of rebar ensures that the concrete structure can withstand the forces it will encounter.

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