Net tensile area of round bars with threaded ends For a round bar in tension with threaded ends, the net area to be used for tensile capacity is the cross-sectional area measured at which location?

Introduction / Context:
Tension members with threaded ends (such as tie rods) experience their smallest net area at the root of the thread. Design must therefore be based on the weakest section to avoid overestimating strength.

Given Data / Assumptions:

• Round bar with standard threads at the ends.
• Failure is governed by tensile rupture at the weakest cross-section.
• Nominal (major) thread diameter is larger than the minor (root) diameter.

Concept / Approach:
For threaded bars, metal is removed at the threads, reducing the net load-carrying area. The smallest area occurs at the thread root. Using this net section in stress calculations safeguards against fracture at the threaded region.

Step-by-Step Solution:

Verification / Alternative check:
Fracture surfaces of failed threaded rods typically occur at or adjacent to the first engaged threads, corroborating that the root is critical.

Why Other Options Are Wrong:
Mid-section (shank) has a larger area unless reduced; difference of areas is not a physical section; any location is unsafe; nominal diameter overestimates area.

Common Pitfalls:
Using nominal diameter to compute capacity; ignoring stress concentration near the first engaged thread.

Final Answer:
Root (minor diameter) of the thread