in structural mechanics, a system of supporting members of a structure (or a structural model of such a system) characterized by a three-dimensional distribution of the forces in the system’s elements; it can be formed from individual two-dimensional systems interconnected by couplings. Depending on the design features and the nature of the mechanical stress occurring in the system, three-dimensional systems are classified as truss, thin-walled, monolithic, or composite.
Three-dimensional truss systems are made up of elements (trusses) in which one dimension (length) is much larger than the other two. They are used in such structures as towers and power transmission line towers; they are also used as the supporting members of space frames.
Three-dimensional thin-walled systems are made up of elements having one dimension that is much smaller than the other two; such elements include sheets and shells. These systems are widely used in engineering and construction in the form of shells, vaults, marquees, folded prismatic systems, and sheet-metal structures, such as pipes, storage tanks, and gasholders. They make it possible to reduce substantially the amount of construction material used and the weight of the supporting members.
Monolithic three-dimensional systems are structural systems in which all three dimensions are of approximately the same order. They include the foundations of various structures, dams, retaining walls, and housings for atomic reactors. The improved strength characteristics of the materials used for these structures and the development of design techniques methods is making it possible to replace massive three-dimensional systems with more efficient thin-walled systems.
Composite three-dimensional systems are a combination of various systems, such as a truss system with a thin-walled system or a thin-walled system with a monolithic system.
L. V. KASAB’IAN