Continuous floor slab layout: If the interior (intermediate) span of a continuous reinforced concrete slab is 5 m, what length is commonly adopted for each end span to obtain practical continuity and economy?

Introduction / Context:
During framing layout of continuous slabs/beams, end spans are often selected slightly shorter than interior spans to control negative moments at supports, improve serviceability, and fit architectural grids. This rule-of-thumb planning concept is frequently examined in building design.

Given Data / Assumptions:

• Interior (intermediate) span = 5 m.
• End span is commonly set as a fraction of interior span for practical continuity.
• Typical building design guidance is assumed.

Concept / Approach:
A widely used planning guide is to take end spans at about 0.9 of the interior span in continuous systems. This leads to smoother moment distribution, ease of detailing, and better control of deflection and cracking at exterior supports.

Step-by-Step Solution:
Compute 0.9 × 5 m = 4.5 m.Compare with offered choices.Select 4.5 m as the adopted end-span length.

Verification / Alternative check:
Design handbooks and practice notes commonly reflect the 0.9L guideline for preliminary layout; final design still requires rigorous analysis.

Why Other Options Are Wrong:

• 4.0 m, 3.5 m, 3.0 m: excessive reduction, not a common planning proportion for continuous slabs.
• None of these: incorrect because 4.5 m is a recognized practice value.

Common Pitfalls:
Treating preliminary span proportions as a substitute for full structural analysis; ignoring actual support conditions and loading variations.

Final Answer:
4.5 m