Pioneering hypar thin shell concrete roofs in the 1930s

The paper explores the conditions of emergence and first applications of thin hypar concrete shells. They appeared in France in the 1930s in the context of building hangars for aircraft and roofs for workshops at air or naval bases. Two French engineers were mainly involved in the development of this form: BERNARD LAFFAILLE, who began designing conoid shells in 1927 but actually never got the opportunity to build concrete hypars, and FERNAND AIMOND, who established the membrane theory of the hypar in 1932 and applied it to design and construct several HP roofs in 1934-1939. The paper describes these forgotten structures and recalls the influence of AIMOND's contributions from the mid-1930s on the subsequent widespread adoption of the hypar.