Lattice structures
Introduction
In structural engineering, a truss or lattice is a lattice structure of straight bars interconnected at nodes forming flat triangles (in planar lattices) or three-dimensional pyramids (in spatial lattices). In many countries they are known as armor or reticulated. The interest of this type of structures is that the bars work predominantly in compression and tension, presenting comparatively small bendings. The term is taken from the traditional architectural lattice "Lattice (architecture)".[1].
Lattices can be built with various materials: steel, wood, aluminum, etc. The joints can be articulated or rigid. In trusses with articulated nodes, bending is negligible as long as the loads that the truss must support are applied to the joints connecting the bars.
A truss is a gabled lattice with variable depth.
History
The first lattices were made of wood.
The Greeks already used wooden lattices for the construction of some houses.
In 1570, Andrea Palladio published I Quattro Libri dell'Architettura, which contained instructions for the construction of truss bridges made of wood.
Classification of lattices
Flat lattices
The flat lattices of articulated nodes can be divided from a structural point of view into:.
If a plane lattice has rigid nodes, then it is hyperstatic regardless of the number of nodes and bars. In these cases they are usually calculated approximately assuming that their nodes are articulated (if they are similar to a simple or compound lattice), or reasonably more accurately by the matrix method of stiffness.
Statically determined planar trusses
A lattice is called statically determined or totally isostatic if the mechanical equilibrium equations are successively applied, first to the entire structure, to determine its reactions, and then to the internal parts, to determine the stresses on each of the elements that make it up. These two conditions are called: