Clear Span vs Effective Span

The clear span is simply the unobstructed clear distance between the inner faces of two supports. The effective span, which is what is actually used in bending/deflection analysis, is defined by IS 456 Cl. 22.2: for simply supported members it is the lesser of (clear span + effective depth) or (centre-to-centre of supports); for continuous members it is generally the centre-to-centre distance (with adjustments where support width is large); for cantilevers it is the length to the face of the support plus half the effective depth.

Getting this distinction right matters: using clear span where effective span is required (or vice-versa) mis-states the design moment (∝ span²) and the span/effective-depth deflection check, leading to either unsafe under-design or uneconomical over-design. It is also fundamental to the effective-depth and minimum-depth (span/depth ratio) rules of Cl. 23.2.