Effective span rules for beams and slabs — identify the correct statement(s) (Use IS code practice; consider clear span, effective depth, and centre-to-centre of supports.)

Introduction:
In reinforced concrete design, the effective span determines bending moments and deflections. Codes specify how to measure spans depending on support conditions and continuity. This question checks familiarity with code-consistent definitions used in beams and slabs.

Given Data / Assumptions:

• Simply supported versus continuous members.
• Slabs and beams follow the same span logic for many cases.
• Roller/rocker bearings are special supports with defined bearing centres.
• Support width is assumed small relative to span.

Concept / Approach:
The effective span is the controlling dimension for analysis. Codes permit taking the lesser of two measures to avoid overestimating span: (clear span + effective depth) or the centre-to-centre of supports. This reflects how compression struts and tension ties develop within the member depth and through bearing widths.

Step-by-Step Solution:
1) Simply supported beam: adopt min(clear span + effective depth, centre-to-centre).2) Simply supported slab: same rule applies because the slab behaves as a flexural member spanning between supports.3) Continuous beam/slab: the same minima logic applies; supports are often narrow relative to span, justifying the rule.4) Roller/rocker bearings: the span is taken between bearing centres by definition.

Verification / Alternative check:
Design examples show small changes in effective span can noticeably change design moments; using the lesser value is conservative and code-aligned.

Why Other Options Are Wrong:
Each statement A–D is individually correct; therefore “All of the above” is also correct and the best choice here.

Common Pitfalls:
Confusing clear span with effective span; ignoring the member depth; or using face-to-face distance when code requires centre-to-centre for some supports.

Final Answer:
All of the above.