In Dutch, when someone is talking about rebar, he will litterally translated say “a bar round 8”. But, as you can see in the picture below, rebar isn’t round at all. And so there is not one fixed, pure diameter and you have to take that into account in practice. Read the story about the diameter of rebar here.
Figure 1 Cross-section of reinforcing steel, no bar is cleanly round.
The start of the production process of reinforcing steel is in the blast furnaces, from where so-called billets of iron are brought to rolling mills. Here the rebar is given its correct shape. By means of rolling the billets or coils, different cooling methods and/or stretching or drawing, bars of different thicknesses are created. The ultimately intended diameter and quality determine which method is most suitable. During these methods, rib or dent profiling is also applied to facilitate adhesion to the concrete and the transmission of forces. As a result, the bar is no longer perfectly round.
The agreement is that a profiled bar size 8 must be produced in such a way that the volume and mass are equal to an imaginary bar with the same length and a pure diameter of 8 mm. A deviation tolerance of +/- 4.5% is allowed. When we, in the Netherlands, talk about round 8, in official terms it is called a nominal diameter of 8. A nominal diameter is a dimensionless index number. Working with nominal values is practical and makes it easy to communicate with each other.
Figure 2 Nominal diameter of rebar
Nice those agreements and imaginary round bars, but is it all right? That is of course tested and monitored. Because building material must comply with European codes and standards. For example, a certificate of reinforcing steel indicates the nominal diameter of the ordered material and what the measured values are. The actual cross sectionel area is assessed. See figure 3. With a diameter of 12 mm, the cross area is πr2 = π62 = 113.1 mm2. Thus, during the tests on this batch, it has been found that the actual cross sectional areas are close to that value and are within the tolerances allowed.
Figure 3 Part of a 3.1 certificate in which the diameter of reinforcing bars has been checked.
In practice it is important to take into account that bars of reinforcing steel are not cleanly round. If you look in the table below, you can see that for a bar size 10, the practical diameter D can be 11.6 mm (varies by manufacturer). For example, if you have to put a hairpin link at the end of a rebar cage, there is a chance that the hairpin will not fit properly if you do not take the actual diameter into account in advance. For example it is known, that the outer dimension of the rebar cage is 230 mm. and the bars are size 10. In practice, the inner dimension of the cage is not 210 mm, but can be 206.8 mm. Also the bars of the hairpin link are not exactly 10 mm. Then it can be difficult to insert the hairpin link if you had calculated exactly 10 mm. for the width of the hairpin link.
Figure 4 The actual shape and dimensions of a cross-section of reinforcing steel.
Reinforcing steel is also regularly applied through holes. For example, when an annex to a building is made, holes are drilled in the existing concrete. When drilling the holes, the actual diameter of the reinforcing steel must of course also be taken into account. When a nice round hole with a diameter of 8 mm is drilled, that bar Ø8 with a D1 of 9.3 mm (see figure 4) will not fit in it. Click here for an overview of the actual, practical diameters of reinforcing steel.
Betonstaal.nl supplies a wide range of diameters of rebar from 6 to 32 mm. Reinforcing mesh are supplied from 4 to 12 mm. Do you need different diameters or do you have a different reinforcement request? We have a passionate team of reinforcement specialists ready for you. Please contact us.
