A brief introduction on Beams

1. Project
Report
February 4
2015
Project Members.
1. Saud zaman (reg#3648) D
2. Tariq aziz (reg# 3617) D
3. Azeem waqar (reg#3610)D
4. Asad mehmood(reg#3634)D
BEAMS

2. Beams
 Introduction to beams.
A beam is a structural element that is capable of withstanding load primarily by
resisting bending. The bending force induced into the material of the beam as a result of
the external loads, own weight, span and external reactions to these loads is called
a bending moment.
Beams are traditionally descriptions of building or civil engineering structural elements,
but smaller structures such as truck or automobile frames, machine frames, and other
mechanical or structural systems contain beam structures that are designed and
analyzed in a similar fashion
 Structural characteristics
Moment of inertia
The moment of inertia of an object about a given axis describes how difficult it is to change its
angular motion about that axis. Therefore, it encompasses not just how much mass the object has
overall, but how far each bit of mass is from the axis. The farther out the object's mass is, the more
rotational inertia the object has, and the more force is required to change its rotation rate.
Stress in beams
Internally, beams experience compressive, tensile and shear stresses as a result of the loads
applied to them
 Types of beams
In engineering, beams are of several types:[2]
1. Simply supported - a beam supported on the ends which are free to rotate and have no
moment resistance.
2. Fixed - a beam supported on both ends and restrained from rotation.
3. Over hanging - a simple beam extending beyond its support on one end.
4. Double overhanging - a simple beam with both ends extending beyond its supports on both
ends.
5. Continuous - a beam extending over more than two supports.

3. 6. Cantilever - a projecting beam fixed only at one end.
7. Trussed - a beam strengthened by adding a cable or rod to form a truss.
For example.
 Cad drawings of beam

4.  Dezign of beams and Applications.
1. Bridges
2. Steltech: Steltech Tri-beam
3. Spreader beams
4. Cranes.

5.  failures in beams
A beam may fail in one of three ways. The three types of failure are material failure causing
a plastic hinge to form, lateral-torsional buckling along the length of the beam, and local
buckling of the beam cross-section.
Bending strength may be limited by material strength, lateral-torsional buckling or local
buckling.
As was stated previously the strength of a beam depends on its maximum moment and
shear capacities, and these depend on the relevant allowable stresses.
A plastic hinge forms when the bending stress reaches the material yield strength.
Collapse by formation of a plastic hinge. Where the stress in the beam reaches the yield
stress, the bending moment cannot be increased and the beam collapses.
Lateral-torsional buckling is associated with the compression developed in part of the beam
cross-section due to bending. Bending moments cause a pair of internal horizontal forces,
one force is a tension force and the other a compression force. The tension force stretches
one side of the beam. This force, like pulling a string, tends to keep the tension side of the
beam straight between supports.
However, the compression force can buckle the compression side of the beam. Because
the tension force is keeping one side taut, the beam can only buckle sideways and twist the
beam - hence lateral torsional buckling.

6. Tension and compression due to bending
Effect of tension maintaining straight form of beam
Effect of compression causing lateral-torsional buckling

7.  Needs of improvements
Lateral-torsional buckling may be resisted by restraining the beam laterally.
This buckling may be prevented by adequate lateral restraint preventing sideways
movement of the beam. If this is at discrete points, the beam may buckle between these
points.
Buckling of beams with intermediate restraint
Steel floor beams are often adequately restrained by the floor slab.
In building structures the floor slab is often able to provide effective restraint to the floor
beams, preventing lateral-torsional buckling. In such cases the beams can be designed on
the basis of the full bending strength.
Local buckling can occur if the beam cross-section is very slender.
If some part of the beam is very slender, then this may buckle locally. In practice, standard
steel sections are proportioned so that this is not a critical design consideration.
Local buckling of beams
The dominant failure mode depends on a number of factors.
Which type of failure occurs depends on four factors:
 the slenderness ratio of the beam.
 the shape of the bending moment diagram.
 the proportions of the individual parts (webs, flanges etc.) of the beam cross-section.
 the presence of a "high" shear force.
Any of these factors may reduce the allowable stress to below the yield stress to ensure
that the beam is safe against any type of failure.