Section Modulus

                                            Section modulus

The moment carrying capacity of an object is directly dependent on geometrical property (I) and material property (E) of an object,which is collectively termed as flexural rigidity(EI).Geometry of an object plays an important role in load bearing capacity of an object which is indicated by moment of inertia of a section. Therefore section modulus is the predominant factor which evidences the strength of an object and is defined as the ratio of the moment of inertia of the object about its centroidal axis to the distance of the extreme fibers of the object from the neutral axis.

Section modulus is generally denoted by Z.

Therefore ,  Z = I / Ymax 

where, I = Moment of inertia of a section.

          Ymax = Distance of the outer most fiber of the object from the neutral axis.

Section modulus can also be defined by using the simple bending theory as,

we know that, M / I = σ / Y

Therefore, Z = M / σ 

i.e, section modulus is also expressed as the ratio of bending moment to the bending stress of a given object within the elastic limit.

Significance of section modulus

1. Section modulus is the important factor for design of beam and flexural member
2. Higher the value of section modulus, higher will be the resistance of member to bending
3. It is required to calculate stresses in beams.
4. It is used to calculate strength of the steel structure
5. More the section modulus, it can withstand more load and it is also considered to be more tougher.