Effective flange width limits for an L-beam (edge T-beam): According to standard R.C.C. practice, the effective flange width should not exceed multiple geometric limits. Which option correctly states the governing selection?
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AOne-sixth of the effective span only
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BBreadth of the rib + four times slab thickness only
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CBreadth of the rib + half the clear distance to the next beam only
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DThe least of the above limits (apply all and take the smallest)
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ENone of these
Answer
Correct Answer: The least of the above limits (apply all and take the smallest)
Explanation
Introduction / Context:Effective flange width is an idealized width used to model the contribution of the slab to an L- or T-beam in flexure. Codes place upper bounds so that analysis does not overestimate slab participation.
Given Data / Assumptions:
- Edge (L) beam where slab participates on one side.
- Typical geometric limits involve span fraction, slab thickness multiple, and spacing to adjacent beam.
Concept / Approach:All relevant limits must be checked and the smallest value adopted as the effective flange width. This ensures conservatism and prevents unrealistic overestimation of beam capacity from slab flanges.
Step-by-Step Solution:List code-style limits (e.g., span fraction, bw + k·Df, spacing-based).Evaluate all three for the given geometry in design.Adopt the least value as bf,eff.Hence, select option (d): “least of the above.”
Verification / Alternative check:Worked examples in R.C.C. texts always compute each limit and then choose the smallest for design bending capacity.
Why Other Options Are Wrong:
- (a), (b), (c) individually can be either too conservative or unconservative depending on geometry.
- (e) is incorrect because (d) states the correct procedure.
Common Pitfalls:Using only one limit; forgetting that edge beams have different limits than internal T-beams; not checking rib breadth and slab thickness influence.
Final Answer:The least of the above limits (apply all and take the smallest)