Methods for calculating Moment of resistance for Doubly reinforced beam
In our article series for “Doubly reinforced sections”, we have covered the following:
Also check out: “Singly reinforced Sections” article series.
Now, our next step would be to study different methods for calculating moment of resistance (MR).
Two methods for calculating Moment of Resistance
There are two methods for calculating the moment of resistance of doubly reinforced sections. They are as follows:
- Method 1 – Elastic theory
- Method 2 – Steel beam theory
Method using Elastic theory
The moment of resistance is calculated by taking the moments of forces about the centre of gravity of the tensile steel.
From the figure above, we get,
Mr = Moment of compressive force of concrete about tensile steel + Moment of equivalent concrete force of compression steel about tensile steel
= bx(σcbc/2)(d – x/3) + (1.5m – 1)Asc. σcbc (d – d’)
Where, (1.5m – 1)Asc is the equivalent concrete area of compression steel.