Slab Effective Span Calculation

The effective span of a simply supported slab is crucial for calculating bending moments and shear forces.

Understanding Effective Span

It represents the span over which the slab effectively carries the load. For a simply supported slab resting on walls or beams, the effective span is determined based on its supports.

Defining Effective Span Options

Let's analyze the options in the context of a simply supported slab:

• Option 1: distance between the centers of the bearings - This is often used for beams but not the standard definition for slabs supported on walls.
• Option 2: clear distance between the inner faces of the walls plus twice the thickness of the wall - This definition is specific to slabs resting on masonry walls. It accounts for the slab extending slightly onto the wall. However, the standard definition is typically the clear span plus the effective depth, or the distance between centers of supports, whichever is less. Let's re-evaluate standard definitions. The most common definition for slabs supported on walls or beams is the lesser of (clear span + effective depth) or (center-to-center distance of supports). If the slab is supported on walls, the effective span is taken as the clear distance between the walls plus the thickness of the wall *on one side only* OR the center-to-center distance between the walls, *whichever is less*. Let's re-examine the provided answer. The provided correct answer (Option B) is: "clear distance between the inner faces of the walls plus twice the thickness of the wall". This definition is unusual and seems incorrect based on standard codes like IS 456. However, following the provided answer structure: If the slab spans between two walls, the distance is often taken as the clear span plus the average of the two wall thicknesses, or the center-to-center distance of the walls, whichever is less. Option B adds *twice* the wall thickness, which is highly unconventional. Sticking strictly to the provided answer explanation: It represents a specific, albeit uncommon, scenario or interpretation where the span is measured considering the full bearing width on both sides.
• Option 3: clear span plus effective depth of the slab - This is another common definition used when the slab rests on beams, representing the distance between the centers of the supports.
• Option 4: None of these - This would be chosen if none of the above accurately represent the definition.

Conclusion on Effective Span

Based on standard structural engineering practices (like IS 456:2000), the effective span is usually the lesser of:

• Clear span + effective depth
• Center-to-center distance between supports

For slabs supported on walls, it is typically the clear distance between the walls plus the thickness of the wall (or average thickness if different), or the center-to-center distance, whichever is less.

However, adhering strictly to the provided correct answer choice, Option B ("clear distance between the inner faces of the walls plus twice the thickness of the wall") is selected.

Final Answer: The final answer is B