What is Truss
A truss is a structural framework consisting of structures or members that are connected at their ends or panel points forming a series of triangles allowing the structure to cover a longer span.
Triangles will not change shape when the lengths of their sides are fixed thus giving structural stability to the shape or design. The munter point is the joint at which a truss is designed to be supported.
Generally five or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes make up the truss.
Under such circumstances, external forces and reactions to those forces act only at the nodes, resulting in tensile or compressive forces on the members.
Whether or not the structural form is stable and efficient depends on the depth of a truss, or the height between the upper and lower chords.
A truss having an optimum depth will maximize its efficiency. Top chords are the top beams in it and are in compression, the bottom chords are the bottom beams and are in tension, the interior beams are called webs, and the areas inside the webs are called panels.
Short video showcases how Trusses work
https://www.youtube.com/watch?v=-qms9xt3sbQ&nohtml5=False Video courtesy of Learn Engineering
Basic types of truss • The pitched type or common type is identified by its triangular shape and is most often used for roof construction. Some common trusses are named according to their web configuration. The chord size and web configuration are determined by the span, load and spacing.
• The parallel chord type, or flat type, gets its name from its parallel top and bottom chords. It is often used for floor construction.
The structural integrity of a truss is largely dependent on its component connections. The most critical connections are those between the truss and its supports.
These connections must be able to resist shear forces acting perpendicular to the plane of the truss and also uplift forces due to wind and may also be required to transfer bending moment besides handling the bearing load.Image below shows a fraction of possible patterns
Other commonly used truss configurations
The Simple truss
However, this can be expanded by adding pairs of members, each connected to two existing joints and to each other to form a new joint.
A planar type is one where all member structures and nodes lie within a two dimensional plane and are commonly used in parallel configurations to form roofs and bridges.
Space frame truss
A space frame type is a three-dimensional framework where members and nodes extend into three dimensions. The simplest form it is the tetrahedron shape, with six members meeting at four joints, an example of which is the base structure of the pylon.
The Pratt type consists of vertical members for compression and horizontal members which respond to tension. It has continued to remain popular even when iron has replaced wood and steel has replaced iron. An example of which is the Southern Pacific Railroad Bridge which consists of 9 Pratt truss spans of differing lengths.
The Bowstring type, named thus because of its shape was used in arched bridges and for supporting the curved roofs of aircraft hangars. There are a variety of arrangements of the members or structures connecting the nodes of the upper arc with those of the lower, straight line-up of members, forming isosceles triangles in some arrangements.
King Post and Queen Post trusses
The king post type is made up of two angled structures leaning into a common vertical structure. While the queen version truss is similar to the king but the outer structures are angled towards the centre of the structure which has a horizontal extension in the form of a beam to provide mechanical stability.
Lenticular, Town’s lattice, Vierendeel trusses The lenticular type have both the top and bottom chords arched, thus forming a lens shape.
The town’s lattice type comprise of planks arranged diagonally with short spaces between them.
The Vierendeel type is made up of rectangular frames and the frames have fixed joints that are capable of transferring and resisting bending moments. Its application is found in buildings which require large amounts of unobstructed space for door openings.
Applications of TrussIt spans from interior to exterior usage and widely used for most types of steel or metal bridges. Famous global iconic structure the Eiffel Tower showcases the potentials and beauty of truss in construction.