Effective Span of Beams with Different Support Conditions
During analyzing a structure the distances between column and between floor beams is generally represented by a simple line diagram using a center line to simplify the analysis. But, In practical cases, the column may have considerable width as well as the beam may have considerable depth leaving some modification of the respective length of these members. As width and depth of column and beam respectively, is accounted in these center line diagram, the derived results (moment, shear, torsion etc.) due to self weight and superimposed loads, from analysis is not practical and reasonable one.
These difference between their center line distances and clear distances raised concept of effective of effective span length which results in a practical substantially accurate value of the results.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.
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| Effective Span of Simply supported beam |
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.
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| Effective Span of Continuous beam |
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.
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| Effective Span of Cantilever beams |