One-way (simply supported) slabs — bar curtailment rule: In a simply supported slab, at what fraction of the span are alternate tension bars commonly curtailed (cut off) from the midspan side towards the support under standard detailing practice?

Introduction / Context:
Curtailment of reinforcement in slabs and beams is used to reduce congestion and improve economy while maintaining structural safety. In simply supported slabs, alternate bars may be curtailed because positive bending moments are highest near midspan and reduce towards supports.

Given Data / Assumptions:

• One-way slab, simply supported.
• Uniform loading scenario typical of floors/roofs.
• Standard detailing practices for bar extension and curtailment.

Concept / Approach:
The intent is to keep full reinforcement where moments are largest and reduce steel where moments diminish. A conventional detailing guideline adopted in many practice-oriented question banks is to curtail alternate bars at approximately 1/7 of the span from the support side, while ensuring minimum anchorage/development lengths are satisfied.

Step-by-Step Solution:
Identify maximum positive moment region at midspan (keep full bars continuous there).Towards supports, moment reduces; alternate bars can be terminated safely at a codified fraction of span while meeting development length requirements.Adopt the common objective-test guideline distance = L/7 from support for curtailment of alternate bars in simply supported slabs.

Verification / Alternative check:
A more rigorous approach would compute actual cut-off points using moment diagrams and development length checks. Nevertheless, the L/7 rule is a frequently cited conservative detailing cue for exam-style problems.

Why Other Options Are Wrong:
L/4, L/5, L/6: These do not reflect the conventional slab-curtailment rule used in such questions; also may not provide the same balance between economy and anchorage.None of these: Incorrect because a commonly accepted proportion exists for such MCQs.

Common Pitfalls:

• Ignoring development length; bars must not be cut where anchorage is insufficient.
• Cutting too close to regions with still-appreciable bending demand.

Final Answer:
1/7 of the span