The aim of the paper is to present the possibility of performing engineering calculations in domains of complex shapes expressed by a mathematical description. We focus on calculations with the Finite Element Method. An example of the complex structure is gyroid, which is a periodic structure representing an area close to the porous structure. The gyroid unit cell exhibits circular struts and a spherical core. A unit cell spatially occupies a cube. The side length of the cube is defined as unit cell size, and the volume percentage of the struts inside the cube is referred to as volume fraction. The periodic cellular lattice structures are generated by repeating the gyroid unit cell. One of the uses of such structures is their employment in additive manufacturing (AM) so-called 3D printing (layer-by-layer AM technique), where they can contribute to reduce the weight of an item and to limit the material consumption. It is important to answer the question of what is the effect on the mechanical properties of an element (e.g. the magnitude compression strength versus the volume fraction) with a gyroid structure compared to a full structure. The paper will also show the results of comparison for different porous structure densities.