Two -way structural concrete slabs are part of most buildings. Compared to other load bearing elements, they are built using large quantities of material. If the required weight and material can be reduced, natural resources and energy could be saved. Based on numerical calculations, this article shows that the amounts of concrete and steel could be saved when a two-way flat slab design is based on the “force follows form” principle and on an efficient use of materials.

Toward this aim, two different types of concrete are used in three layers throughout the height of the cross section. Both outer layers, which are made of regular concrete, carry the bending load and the core layer, made of a lightweight concrete with a low load-carrying capacity, carries the shear load. In addition, the height of the cross section was chosen based on the respective force flow. The calcula-tions showed that up to 51 % weight, 42 % concrete mass and 61 % reinforcing steel could be saved compared to that of a conventional steel reinforced flat slab.