Twentieth-century structural engineering is moving along a different path. The tendency to activate every part of a structural system instead of concentrating the flow of forces into single lines or channels continues to grow. Such systems can expand with full liberty in all directions. This results in certain difficulties. Only tests by means of models and mock-ups can help.
Construction merges with the irrational and sculptural.
About 1900 reinforced concrete was sufficiently developed for shell construction to be possible. Robert Maillart was one of the first to conceive and to develop the idea of using surface tension in the flat or curved slabs of his bridges and mushroom ceilings, eliminating all linear elements. Freyssinet and Maillart their eggshell vaults about 1930. Maillart once said he had got his inspiration from a steam boiler. The directive of a spatial distribution of forces throughout an entire structure has now been extended in many fields.