HOW TO PROVIDE THE REQUIRED AREA OF STEEL IN STRUCTURAL ELEMENTS

Did you know that you don’t need to always check at tables to determine the area of steel of your elements? This video guides you on how to determine the area of steel if you have the spacing of your bars or the number of bars provided at that section.
When carrying out a design of columns, beams and slabs we provide steel members with an area of steel greater than the required. We provide a number of bars whose area is determined from the column’s cross section. In beams we also provide a number of bars whose area is from the beam cross section but we have to specify whether the bars are at the top or bottom of the beam. In slabs we provide reinforcement in terms of spacing in 〖mm〗^2 per meter length of a cross section

In columns and beams Area of steel As (〖mm〗^2) =C.S. A of 1 bar X Number of bars
〖πD〗^2/4 X N where D=Bar diameter & N=Number of bars
For example; Determine the area of steel of 16mm bars
1 bar=〖πD〗^2/4 X N =〖π16〗^2/4 X 1=201〖mm〗^2
2 bars=〖πD〗^2/4 X N =〖π16〗^2/4 X 2=402〖mm〗^2
3 bars=〖πD〗^2/4 X N =〖π16〗^2/4 X 3=603〖mm〗^2
4 bars=〖πD〗^2/4 X N =〖π16〗^2/4 X 4=804 〖mm〗^2
So if a column has 4, 16mm bars its area of steel is 804〖mm〗^2
If a beam has 2, 16mm bars at the top and 3, 16mm bars at the bottom the area of steel is 402〖mm〗^2 and 603〖mm〗^2 at the top and bottom respectively
In Slabs the area of steel is determined from the slab cross section per meter length. An appropriate bar spacing is assumed from which the number of bars is computed. For instance if we have 200mm c/c spacing we have 1000/200=5 bars per meter length of slab cross section. If we have a spacing of 150 the number of bars used is 1000/150= 6.667 bars. Since the bars are fixed center to center, we do not truncate or round off the bar numbers. We just use it as a fraction.
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