Wind loading on tall vertical vessels: the resultant force depends on which geometric factors?

Introduction / Context:
External wind loads are a primary lateral design consideration for columns, towers, and stacks. The overturning moment and shear on supports and foundations arise from the integrated wind pressure over the projected area. Accurate appreciation of what drives wind forces is crucial for mechanical integrity and anchorage design in accordance with structural codes.

Given Data / Assumptions:

• Straight cylindrical shells with typical platforms and nozzles.
• Wind pressure is a function of wind speed and exposure category; here, we focus on geometry dependencies.

Concept / Approach:
Wind force F_wind ≈ p_wind * A_projected * C_d, where A_projected is the projected area normal to wind, and C_d is a drag coefficient that depends on shape. For a vertical vessel, A_projected depends on height and diameter. The shape (including appurtenances, ladders, platforms) affects the drag coefficient, altering the resultant force and moment.

Step-by-Step Solution:

Verification / Alternative check:
Structural standards compute wind loads using shape factors (C_d), gust factors, and terrain categories; each term multiplies the projected area—explicitly height and diameter—and depends on geometry.

Why Other Options Are Wrong:

• Each individual factor (a), (b), or (c) alone is incomplete; all together determine the load.

Common Pitfalls:
Ignoring platform and piping contributions; neglecting dynamic effects (vortex shedding) that depend on diameter-to-height ratio and attachments; not checking local reinforcement at high-wind appurtenances.

Final Answer:
All of the above