Folded plate structures are assemblies of flat plates, or slabs, inclined in different directions and joined along their longitudinal edges. In this way the structural system is capable of carrying loads without the need for additional supporting beams along mutual edges. This technique originated in Germany in the 1920s and became popular in Russia and the United States during the 1930s to construct roofs for industrial warehouses and public buildings. Modern folded plate structures are typically made of cast in situ or precast reinforced concrete, or steel plate.