A beam is a structural element that primarily resists loads applied laterally to the beam’s axis. Its mode of deflection is primarily by bending . The loads applied to the beam result in reaction forces at the beam’s support points. The total effect of all the forces acting on the beam is to produce shear forces and bending moments within the beam, that in turn induce internal stresses, strains and deflections of the beam. Beams are characterized by their manner of support, profile (shape of cross-section), equilibrium conditions, length, and their material.
Beams are traditionally descriptions of building or civil engineering structural elements, but any structures such as automotive automobile frames, aircraft components, machine frames, and other mechanical or structural systems contain beam structures that are designed to carry lateral loads are analyzed in a similar fashion.
CLASSIFICATION BASED ON SUPPORTS
In engineering, beams are of several types
- SIMPLY SUPPORTED – a beam supported on the ends which are free to rotate and have no moment resistance.
- FIXED – a beam supported on both ends and restrained from rotation.
- OVER HANGING – a simple beam extending beyond its support on one end.
- DOUBLE OVERHANGING – a simple beam with both ends extending beyond its supports on both ends.
- CONTINUOUS – a beam extending over more than two supports.
- CANTILEVER – a projecting beam fixed only at one end.
- TRUSSED – a beam strengthened by adding a cable or rod to form a trusses.
SIMPLY SUPPORTED BEAM:-
A simply supported beam is the simplest structural element, as the name itself suggests, it is supported at its both ends, at one end it is pinned and the other is either pinned or rollers are used. It will undergo both bending and shearing and no translational motion is allowed, only sometimes when the roller end is used, of course, the bending and shearing will vary according to the type of load such as UDL(uniformly distributed load), UVL(uniformly varying load), concentrated load etc. Coming to the next part, if both ends are hinged then it will be a fixed beam which is another class of beams, for which every type of load is not applicable, and deflection is rather less, but of course, it can be regarded as a simply supported beam as it supported by two hinge.
A fixed beam is one with ends restrained from rotation. In reality a beams ends are never completely fixed, as they are often modeled for simplicity. However, they can easily be restrained enough relative to the stiffness of the beam and column to be considered fixed.
DOUBLE OVERHANGING BEAM :-
Overhanging: A simple beam extending beyond its support on one end. Double
overhanging: A simple beam with both ends extending beyond its supports.
Continuous: A beam extending over more than two supports.
A continuous beam, i.e. a beam that has more than two supports, is statically indeterminate . The reactions in the supports of a continuous beam cannot be obtained with the equations of static equilibrium only. For the calculation of the reactions in the supports each section is considered as an independent beam. The action of the adjacent part is substituted by a moment in the support between the sections. The equation for determining these moments is known as the theorem of three moments.
A beam that has one fixed end and n roller supports is n-fold statically indeterminate. If both ends of the beam are fixed, then the degree of indeterminacy is equal to the number of supports. The moment in a roller support for a beam with a console is equal to the moment from the load on the console. We calculate the necessary geometrical stiffness of the beam with the equation of elastic stability R = R=M/ECs. The stress in the beam should be less than the beam-specific and material limits, σmax < σcr and σmax < σy.
A cantilever is a rigid structural elements , such as a beam or a plate, anchored at one end to a (usually vertical) support from which it protrudes; this connection could also be perpendicular to a flat, vertical surface such as a wall. Cantilevers can also be constructed with trusses or slabs . When subjected to a structural load the cantilever carries the load to the support where it is forced against by a moment and Sheared stress
Cantilever construction allows overhanging structures without external bracing, in contrast to constructions supported at both ends with loads applied between the supports, such as a simply supported beam found in a post and lintel system.
A beam which is stiffened by a system of braces constituting a truss of which the beam is a chord is called trussed beam. It consists of steel sections (or wooden beams) and struts of steel rods. Trussed beams are used when there is great weight to be supported across wide space without supports from beneath.
REFERNCE TAKEN FROM WIKIPEDIA