Stirrups spacing along a rectangular RC beam: How should the spacing of shear stirrups generally vary along the length of a simply supported rectangular beam under uniformly distributed load?

Introduction / Context:Shear force is highest near the supports and lowest at midspan for a simply supported beam with uniformly distributed load. Stirrups resist shear; therefore, their spacing should reflect the shear force diagram rather than remain constant along the length.

Given Data / Assumptions:

• Simply supported beam.
• Uniformly distributed load.
• Design according to standard RC practice.

Concept / Approach:Nominal shear stress v = V / (b d) is largest near supports because V is maximum there. To maintain capacity and economy, stirrup spacing is closer (smaller) where shear is high and can be relaxed (larger spacing) where shear is lower, i.e., towards midspan.

Step-by-Step Reasoning:Plot shear diagram: V_max at supports; V = 0 at midspan.Detail stirrups with minimum spacing near supports, increasing spacing towards the centre.Comply with code minimum and maximum spacing limits in all regions.

Verification / Alternative check:Running a shear check at critical sections confirms that the most demanding spacing is near supports. Midspan checks usually govern minimum code stirrup provisions only.

Why Other Options Are Wrong:Constant spacing ignores varying shear.Decreasing spacing towards centre or increasing at ends contradicts the shear distribution.Option e is not a recognized pattern for UDL on simple spans.

Common Pitfalls:

• Forgetting special checks near point loads or openings, where local shear may spike.
• Violating code maximum spacing, especially near supports.

Final Answer:increased at the centre of the beam