Cantilever fillers (deflection/control rule): For cantilever filler members in steel construction, the recommended limit for span-to-depth ratio (L/d) should not exceed which of the following values to maintain stiffness and serviceability?

Introduction / Context:
Span-to-depth guidelines are used by designers to ensure members are sufficiently stiff without requiring detailed deflection checks at preliminary stages. Cantilever members are more flexible than simply supported ones, hence stricter L/d limits are adopted to control tip deflection and vibration.

Given Data / Assumptions:

• Member is a cantilever “filler” (secondary) beam or bracket-like element.
• Serviceability (deflection) is the controlling criterion for preliminary sizing.
• Uniform steel properties and typical building loading assumptions.

Concept / Approach:

Cantilevers experience larger deflections for the same span and depth compared with simply supported beams. Hence, designers use a smaller L/d limit, commonly near 8 for initial sizing. This helps ensure adequate stiffness; the final design still requires verification against actual loads and deflection limits set by the project specifications.

Step-by-Step Solution:

Verification / Alternative check:

Textbook tables and practice guides list tighter deflection control for cantilevers, often suggesting L/d around 8–10 to limit service deflections and end rotations without immediate detailed analysis.

Why Other Options Are Wrong:

• 4: very conservative and may be uneconomical in many cases.
• 12, 16, 20: these are more typical of simply supported beams and are generally too slender for cantilevers at the preliminary stage.

Common Pitfalls:

• Using simply supported span-to-depth limits for cantilevers and facing excessive end deflection.
• Ignoring non-structural constraints (e.g., cladding tolerances) that demand stiffer members.

Final Answer:

8.