As we have already discussed in the previous port reinforced concrete beam is a composite section made of concrete and reinforcement. In this post you will get the answer of why we should account for minimum and maximum reinforcement. Concrete is good in compression and is bad in tension. So it is very much required there should be something which will resist the tensile stresses also. Here comes the role of reinforcement, we use steel as reinforcement in most of the structure. Steel is good in tension. So when we combine concrete and reinforcement, the structure becomes good in tension and in compression both.
In load bearing structures, it is quite obvious to use reinforcement. We should design reinforcement in the most efficient way so that its use is optimum. There are different designing procedures available for all the structural systems like beams, columns, foundations and slabs. The steel provides strength to resist tensile stress where concrete is in tension, as in beams and slabs. It supplements the compressive strength of concrete in columns and walls; and it provides extra shear strength over and above that of concrete in beams.
Minimum reinforcement
The main role of minimum reinforcement is to control the cracking of section which normally occurs due to shrinkage and creep or temperature change. The reinforcement helps in reducing the individual crack width. The value of minimum reinforceemnt as per the IS codal provision is :
$$ \frac{A_s}{bd} = \frac{0.85}{f_y}$$
Where,
As is the minimum are of reinforcement
b and d are the breadth and effective depth of the beam section.
fy is the characteristics strength of reinforcement in N/mm2
Maximum reinforcement
The maximum reinforcement is the maximum percentage of reinforcement allowed for a particular section. It is not at all advisable to provide reinforcement more than the maximum percentage of reinforcement. We all are aware of the fact that reinforcement (steel) is a costlier material compared to concrete so it is better to use it efficiently. As the use of more reinforcement will not help the structure to be safe as the concrete will fail under crushing.
As per IS:456 2000, the maximum area of tension reinforcement should not be more than 0.04bD. where b and D is the breadth and overall depth of the section.
Have already discussed about the different reinforced beam sections in this post.
Beam design
- RCC Beam Design is a free app for designing reinforced concrete beams as per Indian Standards.
- RCC Design and detailing could be performed by Limit State Method specified in IS456:2000
- Option to save the design projects in local storage.
- Detailed calculation steps presented for verification and validation.
