The other interesting thing about the Sagrada Familia is that Gaudi based the primary structure on catenary structures.

Off the top of my head, I believe he first made weighted string assemblies of the vaults, such that the string structure is held in perfect tension from the gravitational force of its own weight.

Then by casting the resulting shape in concrete, and flipping the shape over, the resulting structure is optimized for compression. The tensile structure reflects the force of gravity on the string assembly - it is "optimized" for its own weight, so when flipping it over, and swapping the tension members for compression members, we know this new structure is perfectly shaped to distribute internal and self-weight for compression.