this post was submitted on 18 Oct 2025
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A lot. Most of the strength from a beam comes from the top and bottom, because these are the parts that have to stretch or compress most when the beam is bending. The middle part is contributing relatively little for strength.
That is why metal poles are often hollow, that saves a lot of material and weight without losing much strength.
Every part of what you said is wrong.
The middle indeed provides strength, when it is intact. It prevents the top and bottom from additional deflection under load as it takes on part of that stress. That is why there are very strict rules about when and how you can cut a penetration through a load-bearing joist (which, by definition, they all are).
Additionally, metal poles are a cylinder and take an axial compressive load, for which a cylinder is a very good shape; if you tried to support a floor with a wooden cylinder as a joist and the load was lateral to its length, it would likely buckle - its whole shape is hollow so it has the same problems as a joist with the middle cut out.
I'm really proud of how confident you are.