Two Post-tensioned Thin Folded Plates Designed by E. Torroja for San Nicolás Church

The long-span structure of the San Nicolás church was designed in 1959 by the renowned engineer E. Torroja. His innovative solution consists of two Z-shaped folded plates mutually independent spanning 29 m. In this paper the technical advances used by the engineer to carry out its daring structure are explained. A series of ribs provide stiffness to the slabs facing biaxial bending and torsion and support cantilevered roof. The set of post-tensioned tendons contribute to the strength capacity of the slabs as well as avoid the cracking of concrete. Rotation and the horizontal displacement of the plates are released by the twofold articulation of the main frame. The simplified structural design carried out by the engineer is explained and his results are compared with the structural analysis obtained by a virtual finite element model. The aggressive environment caused corrosion in reinforced concrete elements, but not in the post-tensioned concrete plates.