The seminar discusses the importance of the shear center in beam design, particularly in preventing twisting during unsymmetrical bending. It defines the shear center as the point where the loading should be applied to avoid torsion and emphasizes its relevance in construction, especially for structural members like purlins and rafters. The presentation concludes that positioning loads closer to the shear center enhances the load-bearing capacity of channel sections.

1. WELCOME

2. A technical seminar on
“SHEAR CENTRE”
by
N.SUDHEER
M.TECH-MACHINE DESIGN
16481D1509
GUDLAVALLERU ENGINEERING COLLEGE

3. Need to find the location of shear centre?
 In unsymmetrical sections, if the external applied forces
act through the centroid of the section, then in addition to
bending, twisting is also produced.
 To avoid twisting, and cause only bending, it is necessary
for the forces to act through the particular point, which
may not coincide with the centroid.
 The position of the this point is a function only of the
geometry of the beam section. It is termed as shear center
(or) centre of twist (or) flexural centre.

4. What is meant by unsymmetrical bending?
If the load line on a beam does not coincide with one
of the principal axes of the section, the bending takes
place in a plane different from the plane of principal
axes (or) centroidal axis. This type of bending is
known as Unsymmetrical Bending.

5. Fig: Unsymmetrical bending of
C-section

6. Reasons for unsymmetrical bending?
 The section is symmetrical about two axes
like I-section, rectangular section, circular
section but the load-line is inclined to both
the principal axes.
 The section itself is unsymmetrical like
angle section or a channel section (with
vertical-web) and load-line along vertical
any centroidal axes.

7. Now, what is shear centre?
 Shear center is defined as the point on the
beam section where load is applied and no
twisting is produced.
- At shear center, resultant of internal forces
passes.
- On symmetrical sections, shear center is the
center of gravity of that section.
- Such sections in which there is a sliding
problem, we place loads at the shear center.

8. Properties of shear centre:
 The shear center lays on the axis of symmetry.
 Thus for twice symmetrical section the shear centre is the point
of symmetry axes intersection.
 If the cross section is composed of segments converging in a
single point, this point is the shear centre.
 The transverse force applied at the shear centre does not lead to
the torsion in thin walled-beam.
 The shear centre is the centre of rotation for a section of thin
walled beam subjected to pure shear.
 The shear center is a position of shear flows resultant force, if
the thin-walled beam is subjected to pure shear.

9. Determination of location of
shear centre:

10. Shear centre in real life situations:
construction of purlins
Fig: Usage of purlins in
roof construction

11. A purlin is any longitudinal, horizontal, structural member
in a roof.
The point of application of load is important, depending on
the cross section of purlin.
Fig: C and Z- purlins supported by a I-
section rafter

12.  Purlins are most commonly used in rafter
supported work shops, small scale industries, sheds
and also used to support metallic wall sheets.
 “Purlin” function as a form supported by rafters
and are horizontal structural members in a
building, architecture or structural
engineering. They are used to increase roof spans
without the need for increasing rafter sizes or
compromising wall stability.
 A rafter is one of a series of sloped structural
members (beams) that extend from the ridge or hip
to the wall plate, and that are designed to support
the roof deck and its associated loads.

13. Fig: C-section rafters used to support Z-section roof purlins

14. CONCLUSION:
 If an unsupported channel section is loaded closer
to its shear centre, it'll take more load before
buckling than if you put the load over the centre of
the channel, the application being that you can get
more load out of the same member.
 Useful in design of thin walled open steel sections
as they are weak in resisting torsion.

15. THANK YOU