Civil Engineering - UPSC Civil Service Exam Questions - Discussion

@Kaif.

Actually, in this question, it is not asking what is the influence line diagram of bending moment at a section. If it was asked then answer definitely triangular which shows the variation of BM at a particular section. But we have to find the shape of ILD for MAX BM as per question. And for this, we have to find the Max BM at each section of the beam and then connect all points. You will get a curve that is same as x (L-x) /L i.e. parabola. This curve is also known as the envelope of max BM.

Option B is the correct answer.

Is it not a Triangle ?

No parabola is correct.

Answer should be triangle.

It should be Triangular.

How is it parabola? Explain anyone.

How is a parabola? explain please.

It is parabolic, because M max is given by ab/l, which is a two degree curve.

Because the coordinate of max BM is z (1-z/l) which gives a second-degree curve and hence a parabola.