Torsional Buckling of Beams Report

Running Head: TORSIONAL BUCKLING 1
Torsional Buckling of Beams Report
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Torsional Buckling 2
TABLE OF CONTENTS
ABSTRACT....................................................................................................................................3
1 INTRODUCTION...................................................................................................................4
2 DISCUSSION..........................................................................................................................5
2.1 Buckling............................................................................................................................5
2.2 Concepts............................................................................................................................7
2.2.1 Beam Orientation.......................................................................................................7
2.2.2 Boundary Conditions.................................................................................................8
2.2.3 Cross section..............................................................................................................8
2.2.4 Centre of gravity (COG)............................................................................................8
2.2.5 Shear Center (SC)......................................................................................................9
2.2.6 Center of Twist (COT)...............................................................................................9
2.2.7 Load Application Point..............................................................................................9
2.2.8 Warping...................................................................................................................10
2.3 Lateral Deflection...........................................................................................................10
2.4 Torsion............................................................................................................................11
2.5 Lateral Torsional Buckling.............................................................................................12
2.6 Mechanism of Lateral Torsional Buckling.....................................................................12
2.7 Factors affecting torsional buckling................................................................................12
2.7.1 Point of load application..........................................................................................12
2.7.2 Conditions of the end supports................................................................................13
2.7.3 Bending Moment Distribution.................................................................................13
2.7.4 Lateral restraints......................................................................................................13
2.7.5 Shape of Cross Section............................................................................................14
3 CONCLUSION......................................................................................................................14
REFERENCES..............................................................................................................................15

Torsional Buckling 3
ABSTRACT
This essay considers lateral buckling in beams. Nearly all construction comprises of
beams as a structural member. Buckling is a type of structural deformation that occurs in
members under compression such as columns and struts. This phenomenon is less common in
beam as they are normally loaded vertically above the major axis. However, buckling sometimes
occurs in beam sections under compression. Torsional buckling is a form of deformation that is
as a result of twisting due to applied torque and is accompanied by a subsequent bending of the
flange in compression. Several factors affect the magnitude of the lateral torsional buckling to be
expected in beam. Torsional buckling in beams is normally caused by insufficient bracing.
However, there are several measures that can be taken to prevent this form of structural
distortion from happening.

Torsional Buckling 4
1 INTRODUCTION
Beams are horizontal structural members which primarily carry vertical loads. When a
load is applied on a beam, the upper section of the beam experiences compression while the
bottom section experiences tension. Concrete is weak in tension but good in compression. For
this reason, concrete beams have more steel reinforcement at the bottom than at the top. Torsion
is defined as the twisting of a structural member due to the applied torque. Torsion is represented
in N/m2. Unlike the axial loads, torque creates a non-uniform stress distribution in structural
members. For circular sections, twisting occurs along the axis and the cross section remains
circular. However, when torque is applied on non-circular members, the twisting is accompanied
by warping hence the members do not remain plane.
Buckling is defined failure of structural members due to an applied load which is less
than the design load. Failure of members is not members is in no way related to the strength of
the members (Bansal, 2010). Buckling occurs in members under compression. When a load is
applied on a member along its axis, it tends to be displaced along its axis. There is a sudden
sideways displacement of a member from the axis. As loading is increased, the displacement
increases and it ultimately leads to buckling. The member may collapse completely or remain in
the same position and continue supporting loads. Buckling differs from bending which occurs
when a load is applied along the length of the beam axis. Bending normally occurs in beams and
slabs while buckling is common in struts and columns.
From the definitions above, torsional buckling can be defined as the failure of structural
members due to longitudinal twisting of the member (Gupta, 2014). In beams, this type of
buckling usually occurs in I-section beams. Doubly symmetrical sections such as W, and H
sections are not prone to this type of buckling. Torsional buckling in such kind of sections can