Lateral Pile Analysis: Episode 5 - Free Vs Fixed Pile Head

One of the most common questions I receive during design reviews or software demonstrations is:
“Should we model the pile head as free or fixed?”

It sounds simple, but the truth is this decision can significantly influence your lateral pile analysis results.

The connection between the pile and the pile cap determines how the pile responds to lateral loads. In theory, we have two idealized cases:

• Fixed head: The pile head rotation is fully restrained.

• Free head: The pile head can rotate freely relative to the cap.

However, true fixity is rare in the field. Pile caps can rotate, and most real-world cases fall somewhere between these two extremes.

A few practical notes to remember:

• Steel piles need about 2–3 diameters of embedment into the cap to approach fixity.

• Concrete piles or drilled shafts are considered fixed only when reinforcement is fully developed into the cap.

• When in doubt — run both cases. Compare the results and, if they show sensitivity, move to a more advanced pile group analysis that includes cap rotation.

This topic (and many similar “field vs theory” discussions) is covered in Chapter 16 – Additional Design Considerations of my new Lateral Pile Analysis course.