Serviceability limits – deflection: For a simply supported steel beam in building work, what is a commonly adopted maximum permitted deflection under service load, expressed as a fraction of the span?

Introduction / Context:Serviceability criteria limit deflections to prevent cracking of finishes, ponding, and user discomfort. For simply supported beams in general building applications, historical working-stress practice specifies an allowable deflection as a fraction of span, depending on usage and finishes.

Given Data / Assumptions:

• Simply supported steel beam in a typical building.
• Service load combination considered (not ultimate).
• No unusually sensitive finishes beyond normal plaster/ceilings.

Concept / Approach:

Commonly adopted limits are in the range L/240 to L/400 depending on occupancy and finishes. A widely cited exam-standard value for general steel floor beams is L/325. More stringent limits (e.g., L/360 or L/400) may be used for vibration control or brittle finishes; less stringent values may be acceptable where finishes are not critical.

Step-by-Step Solution:

Verification / Alternative check:

Many older codes and handbooks list values around L/325 for general building beams; local codes may specify different values for specific occupancies, but L/325 remains a standard exam reference figure.

Why Other Options Are Wrong:

• 1/350, 1/375, 1/400: more restrictive than the commonly quoted general limit; they may be used in special cases but are not the standard value sought here.
• “None of these” is incorrect because a valid value is provided.

Common Pitfalls:

• Confusing live-load-only limits with total-load limits.
• Applying the same limit to cantilevers (typically more stringent, e.g., L/150).

Final Answer:

1/325 of the span.