What is meant by the effective length in beams and how can we calculate it ?

Effective span for simply supported and continuous beams are as follows: 

1) Simply supported beams 

The effective span of a simply supported beam shall be taken as the smaller of the distance between the centers of bearing, or the clear distance between supports plus the effective depth. 

2) Continuous beams

If the width of support is less than 1/12 of the clear span, the effective span shall be taken as stated (1) above. If the supports are wider than 1/12 of the clear span or 600 mm, whichever is less, the effective span shall be as follows:

a) For end span with one fixed and the other continuous or for intermediate spans, the effective span shall be the clear span between supports.

b) For end span with one end free and other continuous, the effective span shall be equal to the clear span plus half the effective depth of the beam or the clear span plus half the width of the discontinuous support, whichever is less.

3) Monolithic frames

In case of monolithic frames, the effective span shall be equal to the distance between intersections of the center lines of the connecting members.

4) Cantilever beams

The effective length of the cantilever shall be taken as its length to the face of the supports plus half its effective depth except where it forms the end of a continuous beam where the length to the center of the support shall be used. 

The effective span of a simply supported beam shall be taken as the smaller of the distance between the centers of bearing, or the clear distance between supports plus the effective depth.