Some civil engineering practitioners and quantity estimators often face daunting challenges in an effort to determine an equivalent in a mass of reinforcement bars (rebars) determined from structural drawings and bar bending schedules. There are existing templates that give one information on this but in the absence of such templates, it becomes necessary that one should know how to do this from the first principle.
In this article, I will show how to determine the mass (kg) per meter of different sizes of rebars commonly used in Nigeria.
Reinforcement bars are usually made of steel and the density of steel is 7850 kgm-3. Assuming that we want to know the weight of 1-metre length of a 6 mm reinforcement bar to be used as a stirrup in beams, we should first determine the volume of the bar. Rebars usually appear round in shape. The volume would be determined using the volume of a cylinder,
V = ((πd2)/4) x h.
In this case, d = 6 mm = 0.006 m and h = 1 m
V = ((π x 0.0062)/4) x 1 = 0.000028274333 m3
Next, we determine the mass of the bar from the density
Density = mass/volume, which implies that, mass = density x volume = 7850 x 0.000028274333 = 0.222 kg
Thus, the mass of 6 mm rebar per metre (m) = 0.222 kg
If the total length of the bar is 500 m, the total mass would be (500 x 0.222) kg = 111 kg
Sometimes, the rebars are sold in Tons. In that case, we should know that 1 ton = 1000 kg
Therefore, 111 kg = (111/1000) ton = 0.111 ton
We can apply this method to determine the mass of all types of bars. We would only vary the diameter of the bar while the density and height or length remain constant. Table 1 presents a summary of the solutions.
Table 1: Mass in kilogram per metre of different sizes of bars