It is common place in many engineering applications to use thin walled sections (i.e. sections in which the material thickness is small when compared co mpared to the other geometrical parameters para meters such as depth and width). When selecting members for use in a particular situation several considerations are necessary, especially with regards to the specific loading conditions it must undergo. One of these considerations is the aforementioned geometry of the section. This is important as the shape of a section enables certain properties to be invoked with benefits dependent of the loads which must be supported, as well as, the reaction of the section to said loads. Thus location of the shear centre becomes an integral part of this consideration. Shear Centre, a property of the cross-section of a structural member, e.g. a beam. It is the point on a cross section through which the resultant shear force must pass for bending to occur without torsion or twisting. (enguin !ictionary of "ivil #ngineering) #$ternally applied forces induce bending moments and shear forces on structural members (for e$ample e$ample beams). In all variations variations of channel sections sections these these forces act through through a point aptly known as the shear centre. %or symmetrical sections such as I&beams, the shear centre coincides with with the neutra neutrall a$is a$is (centr (centroid oid)) or is locate located d on the a$is a$is of symmet symmetry ry.. %or unsymm unsymmetr etrica icall sections, or those in which there is only one a$is of symmetry (such as channel sections), the shear centre does not coincide with the centroid. When a load is applied at the shear centre' only fle$ure (bending) is possible and hence fle$ural buckling. owever, when a load is applied to a member away from the shear centre, twisting of the member ensues and eventually leads to fle$ural or fle$ural&torsional buckling. To avoid twisting and cause only bending, it is important that the forces act through a point which may not coincides with the centroid of the section, hence through some point offset of the section, i.e. the shear centre. s a result channel sections resist torsion when a load is applied at the shear centre.
When a beam is transversely loaded in such a manner that the resultant force passes through the longitudinal shear centre a$is, the beam only bends and no torsion will occur. When the resultant acts away from the shear centre a$is, then the beam will not only bend but also twist. If the loads are applied away from the shear centre a$is, torsion besides fle$ure will be the evident result. The beam will be sub*ected to stresses due to torsion, as well as due to bending. In unsymmetrical sections, if the e$ternal applied forces act through the centroid of the section, then in addition to bending, twisting is also produced. To avoid twisting, and cause only bending, it is necessary for the forces to act through the particular point, which may not coincide with the centroid. The position of this point is a function only of the geometry of the beam section. It is termed as shear center. The point where a shear force can act without producing any twist in the section. In general not the centroid, but a point through which a force transverse to the a$is of a beam section can act and not cause any twisting of the beam section.
