Which Shaft Type has Better Torsional Strength During Installation?

According to the provided content, the comparison of torsional strength between round and square shafts depends on the specific application and load requirements, as the source provides conflicting justifications for both types in different sections:

• Round Shafts: These are described as having a decisive engineering advantage regarding torsional performance. Because of their circular cross-section, they distribute shear stress evenly around the perimeter. This prevents the localized stress risers found at the corners of square shafts, which can lead to premature material distress. Round shafts are preferred for high-torque installations in dense till or weathered rock to reduce the risk of shaft twisting.
• Square Shafts: Conversely, the text also states that square shaft leads provide superior torsional strength compared to round shaft leads of equivalent steel weight. They are specifically recommended for heavy commercial and industrial scenarios where axial loads exceed 100 kips to prevent shaft twist during installation in dense soils or when encountering shallow obstructions.

In summary, while round shafts offer more predictable and uniform stress distribution for most high-torque settings, square shafts are highlighted for their superior strength-to-weight ratio in heavy-capacity commercial foundations.