What is the sagging moment and hogging moment?
Just like shear force can be applied in two direction: Upward and Downward
Just like axial force can be applied as compressive force or tensile force, there are two types of moment. One is sagging moment and other is hogging moment.
i. Sagging Moment:
The moment that makes beam to concave upward is called sagging moment. It is generally taken as positive moment.
In this moment, the upward of beam compresses and downward of the beam extends. So, stresses are developed called bending stress.
ii. Hogging Moment:
The moment that makes beam to concave downward is called Hogging moment. It is taken as negative moment.
The upward point is under tension and below point is at tension.
There is line along axial direction which is under neither compression nor tension. It is called neutral axis. The points below neutral axis is under tension in sagging moment and under compression in hogging moment and the way around in next case.