WHAT IS SECTION MODULUS?
It is a resisting property of cross section of a structural member because of which the member tries to resist the force which causes bending in the member. CLICK HERE
Therefore the safety of the member against bending depends on this parameter and it is directly proportional. That means if section modulus Z increase safety of the member also increase with respect to the members having same cross sectional area but different Z. Therefore we can arrange the following cross sections according to their safety in basis of Z value as :
Stepped section > I section > Rectangular section > Square section > Circular section
Calculation of SECTION MODULUS
We can calculate Z with the help of moment of inertia. We have to carefully take the axis of moment of inertia.To calculate Z we have to take the moment of inertia I of that axis which will resist the bending . When in a cross section load is applied along a axis then it is resisted by the other axis perpendicular to it.Therefore,
Calculation of MOMENT OF INERTIA
For calculation of moment of inertia we can directly use the formulas for different cross section as mentioned in the following table : CLICK HERE
POLAR SECTION MODULUS
In calculation of Torsional stress we have to consider resistance given by whole cross section since torsion try to rotate the whole cross section and since it varies radially.In this case we have to use a new type of section modulus called POLAR SECTION MODULUS.To calculate this Z we have to take moment of inertia which is summation of both the axis of cross section.Thus,
Z = I/R
where I = I(xx) + I(yy) and
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