Column splice design when the upper column does not provide full bearing over the lower column: which assumptions are made for force transfer in the splice?

Introduction / Context:
Column splices are required for construction practicality and alignment. When bearing is incomplete (mismatch of profiles or partial contact), the splice must transfer axial force and any incidental moment safely through plates, flanges, and bolts/welds.

Given Data / Assumptions:

• Upper column does not fully bear on the lower column over the complete area.
• Splice plates and bearing plates are provided.
• Design must account for axial load and possible moment due to misalignment or construction tolerance.

Concept / Approach:
The bearing plate is analyzed as a short (deep) beam spanning between flange/web contact areas of the lower column. Axial load is shared by the flanges and web; flange forces can develop a couple with opposing reactions in the lower column to equilibrate moment. Splice bolts/welds are designed for the remaining forces and to clamp the assembly.

Step-by-Step Solution:

Verification / Alternative check:
Check bearing stresses, plate bending, bolt shear and bearing, and ensure compatibility with column section properties and construction tolerances.

Why Other Options Are Wrong:
Each individual assumption represents part of the complete behavior; the correct comprehensive assumption set is “All the above”.

Common Pitfalls:
Neglecting unintended moments; underestimating plate bending; ignoring erection tolerances and fit-up gaps.

Final Answer:
All the above