“Simple design” (simple construction) assumption for steel frames: Which statement best reflects the principal assumption used in the simple method of steel framework design?

Introduction / Context:
Structural steel frames can be analyzed and designed under different connection assumptions: simple (pinned), semi-rigid, or continuous (rigid). The “simple design” method is common in building frames with shear connections.

Given Data / Assumptions:

• The design method assumes negligible moment transfer at beam–column connections.
• Beams carry gravity loads primarily by bending as simply supported members.
• Columns are designed for axial load with allowances for minimum eccentricity.

Concept / Approach:
In simple construction, connections are detailed to transmit shear and axial force but not significant end moment, so the global analysis treats beams as simply supported. However, design still checks columns for code-specified minimum eccentricities and second-order effects as required. Hence, all three statements are consistent with simple design practice.

Step-by-Step Solution:

Verification / Alternative check:
Connection details such as fin plates and flexible end plates exemplify simple shear connections; moment frames would contradict the “simple” assumption.

Why Other Options Are Wrong:
Choosing only one or two statements would omit integral parts of the simple design philosophy.

Common Pitfalls:
Assuming zero moment entirely and ignoring frame stability bracing; neglecting minimum eccentricity provisions for columns.

Final Answer:
All the above