What Is Buckling of Column in Civil Engineering?
What Is Buckling of Column in Civil Engineering?
In civil engineering, the buckling of a column is the failure which occurs when a structural element (such as a beam, pole or post) is subjected to compressive forces along its longitudinal axis and unable to support them. This happens when the axial load applied increases beyond the capacity for elastic deformation, resulting in an unstable state where the column starts to ‘fold’ into itself.
Buckling usually leads to catastrophic collapse, therefore it needs to be prevented by introducing additional supports or by reducing load on columns.
Buckling is the sudden collapse of a structure caused by too much force placed upon it. It typically occurs when a slender column is subjected to an axial load that creates compression along its length and causes it to buckle.
This creates a corresponding reduction in that column’s buckling load or resistance as it bends or fails under the applied external load, making for a bracing failure mode rather than one due to shear forces.
Buckling can also occur when compressive loading is concentrated at the ends of the columns, leading them to bend outwards from their original position and eventually failing due to excessive loading beyond their elastic limit.
Lateral Torsional Buckling (LTB)
Lateral buckling of a column is the deformation of an unrestrained beam due to the applied loads on its longitudinal axis. The compression flange becomes free to move laterally and also rotates, causing lateral displacement and twisting.
Lateral Torsional Buckling (LTB) is the most common form of column buckling, which occurs when the compressive load exceeds the capacity of the beam section to resist bending around its weak axis.
This type of buckling can be further divided into two types: lateral-torsional buckling (LTB) due to axial force and lateral-torsional buckling due to flexural load or bending moment. The design codes provide guidance on how to avoid this type of failure.
Lateral buckling can cause catastrophic structural failure in columns if not carefully considered during design and construction. Therefore, designers must understand and account for lateral buckling when engineering structures for safety.
What Are The Different Types Of Buckling In Compression Members?
Buckling is the failure mode generally resulting from structural instability due to compressive action on the structural member or element involved. There are five main buckling types: Elastic Buckling, Inelastic Buckling, Column Buckling, Local Buckling, and Interactive Buckling.
- Elastic buckling is characterized by elastic deformation before failure following a gradual increase in loads.
- Inelastic buckling involves plastic deformations before failure following an abrupt increase in loads.
- Column buckling occurs when a slender column or beam fails due to excessive compression along its length.
- Local bucking is a type of instability that results from lateral loadings on short members with large cross-sectional areas.
- Interactive bucking occurs when two loading conditions interact and cause sudden failure.
What Causes Buckling?
Buckling is caused when a structural member, usually a column, and experiences compressive stresses that are too high for the material to withstand and results in a sudden sideways displacement.
Compressive or axial forces cause buckling as they are most commonly found in columns rather than beams and thus require a buckling check in most cases.
The strength and stiffness of the material will determine how much force can be applied and how much buckling can be tolerated before failure occurs.
What Are Linear And Nonlinear Buckling?
Linear buckling is a mathematical analysis technique used to identify instabilities in structures that are small and have a linear response to external perturbations.
On the other hand, nonlinear buckling analysis looks for instabilities that arise from heavier loads or geometric nonlinearities. In linear buckling, the structural stability is predetermined by pre-defined small perturbations in the system, which can be easily solved using finite element methods.
For nonlinear buckling, however, the perturbations must be developed geometrically as part of the solution, with no prior definition of the magnitudes and directions of said perturbations.
Nonlinear buckling analysis is, therefore, more complex and usually requires numerical simulation or iteration techniques to predict possible instabilities accurately.
What Is Compressive Buckling?
Compressive buckling occurs when a structural member is loaded in compression, causing it to deflect outwards, similar to bending.
This phenomenon is commonly referred to as Euler Buckling Load, and the amount of force required to cause buckling can be calculated using an equation derived by Leonard Euler in 1757.
Compressive buckling can occur in all shapes of structures and materials. However, it is more likely to happen in long slender columns due to the higher stress concentrations caused by their geometry.
For a structure not to buckle under compressive loads, it must be designed with enough strength through the cross-sectional area so that the load exceeds the Euler Buckling Load before being applied.
How Do You Prevent Buckling?
To prevent buckling, it is important to determine if buckling is a governing failure mode by calculating the compressive load applied (P) and cross-sectional area of column (A). The critical buckling load can be substituted for P in cases where the actual applied loads are unknown.
The larger the cross-sectional area or stiffer material used, the less likely buckling will occur. Therefore, selecting materials and designs that can handle higher stresses with increased stiffness and strength helps to reduce the chance of buckling.
Additionally, applying external restraints can also reduce the likelihood of buckling since it prevents lateral displacement of an unsupported column.
