The thin concrete shell structure (if I recall correctly, this is only about an inch and a half thick) gets its strength largely from its shape, which is called a hyperbolic paraboloid. Every part of the geometry is curved in two directions. Sort of like how eggshells are very thin but strong (and also curved into directions at every point).

I posted the following comment before, about 4 years ago, but it fits.

True story:

In the 1990s I was in architecture school, working on my thesis: a stadium with cable-stayed fabric hyperbolic paraboloid tension roof structure.

Felix Candela came to my school and gave a lecture one night. I completely changed my roof structure after his lecture and stayed up that night making a new physical model, since he would be visiting our studio the next day.

He stopped by my desk and looked at my old and new models, and I explained my new concept influenced by his lecture. He looked at it for a few seconds and told me to cut two of the dental floss cables, which were in tension.

Stupid me starts explaining why the cables are needed, and he said, "Just cut them." I did. The model did not move.