Filler (secondary) joists in steel floors: which statement is correct regarding their detailing and support?

Introduction / Context:
In steel floor systems, main beams carry secondary members called filler (or jack) joists. Understanding their connections and support conditions is important for layout and constructability.

Given Data / Assumptions:

• Typical multi-beam floor framing.
• Secondary joists span between main beams/girders.
• Conventional riveted/bolted or welded detailing with cleat angles.

Concept / Approach:
Filler joists are commonly detailed as continuous across multiple supports when practical and are connected to main beams using cleat angles that transfer shear and provide lateral restraint. The main beams provide vertical support to the filler joists.

Step-by-Step Solution:

Verification / Alternative check:
Standard steel detailing manuals show joist-to-beam connections via cleat angles or shear tabs; continuity depends on layout and is not limited strictly to three supports.

Why Other Options Are Wrong:
(a) confuses reinforced concrete with steel beams in PCC; (b) is overly restrictive—continuity depends on design and layout; selecting only (c) or only (d) ignores the paired correctness.

Common Pitfalls:
Assuming moment connections where only shear is intended; overlooking bracing or deck diaphragm roles.

Final Answer:
Both (c) and (d) are correct