Rebar (reinforcement bar )is a molded steel bar (hot rolled) to create a specific cross-section in order to increase a concrete’s tensile strength. The shape on the reinforcement bar surface is there to anchor the rebar to the concrete after the concrete has been hardened.
Manufacturing The type of metal used to manufacture rebar is steel. Steel has different impurities in it, adjusting these impurities will result in different characteristics (behavior) of the final output.
Carbon is one of the steel elements, carbon increases in steel make the rebar brittle but strong. As our structure is preferred to be ductile, the ideal reinforcement bar has a low carbon content.
Classification Rebar can be classified in different forms but mainly they are classified into two
Size Grade (strength) Size The size of rebar refers to the variation in the rebar’s diameter (cross-section). The usual diameters manufactured are 8, 10, 12, 14, 16, 18, 20,24 and 38 mms. Although these sizes are common, ranges might go higher or lower. 8- means rebar with an 8-millimeter diameter. A comparison of size must be done with only rebars that have the same grade.
Grade The grade designation is equal to the minimum yielding strength of the bar. For a US customary unit 1ksi (Kilogram per Square Inch) equals to 1000psi(Pounds per Square Inch). For instance, if the grade of the rebar is 60 it means it has a yielding strength of 60000psi.
In Europe customary unit grade 60 has a carrying capacity if 420mpa(Mega Pascal). It should be noted that as the grade of the rebar increase the yielding strength increases. In Ethiopia, this is the commonly used measurement unit.
Grade 40,60 and 75 are the most commonly used reinforcement bars and are considered to be economical, higher grades are also available with grade 85 and above. Based on the designer, he/she can use more number of rebar with grade 40 or decrease the number of bars and use grade 75, if carefully designed the strength(output) will be the same. This is all up to the designer’s choices and the cost that might be incurred.
In short, the grade difference is purely on the yielding strength of the reinforcement bar, by altering the number of bars and the grade we can achieve the same strength required.