Last edited 15 Sep 2020

Mechanisms of structural failure


[edit] Introduction

Structural failure refers to defects in which a load bearing component of the building is unable to support and transfer loads to another element. Structural failure develops due to breakdown in the performance of the materials in a structural component may be caused by:

[edit] Compressive and tensile failure

Compressive failure can be sudden and catastrophic, apparent by cross breaks caused by the excessive longitudinal compression or bending. Tensile failure can be detected by stretching in the sizes of the member. These elongations come along with cracks that orient perpendicular to the direction of the tensile forces.

[edit] Bending failure

Bending is the bowing deformation of a beam or other member under load. Bending stress can be slow or sudden depending on the nature of the force applied, whether compressive or tensile forces.

[edit] Shear failure

Shear failure is principally an internal splitting force caused by two forces acting in opposite directions at a distance to one another along the cross section of a structural member. Shear cracks are diagonal, for example, appearing in the web of a beam.

[edit] Buckling failure

Buckling is a creasing failure by crumpling of a longitudinal structural member loaded eccentrically with a compressive force. It occurs to long and slender members subject to axial compressive stress. Buckling load is a compressive load at which a column or strut begins to buckle. Steel columns are more prone to buckling than concrete columns because they are more slender. Also slender beams and floor joists fail due to compressive stresses resulting from the bending.

Buckling Vs. Bending

Buckling Bending
Occurs when the load reaches a certain critical value known as Critical load Occurs under all magnitudes of loads applied to a structural component.
Buckling takes place abruptly. May be sudden or gradual, it gives warning signs of failure of the structural component before complete collapse.
Buckling under load members become unstable, but will generally not fracture Bending under load member deflects, it may start to develop some cracks.
Instability caused by buckling in one member can lead to excessive stresses in other members causing progressive collapse of the whole structure. The defects developed due to bending stress cause less effect to progressive failure of the whole structure.
Buckling is due to axial stresses applied along the longitudinal axis of the member. Bending is a combination of tensile and compressive stresses.

For a member to withstand loads against buckling failure it should be designed to reduce its slenderness by increasing its cross-sectional dimension.

Bracing a member at its intermediate points along its length or height

For economical reasons consider bracing a member as cheaper and easier than increasing its cross sectional dimensions this is uneconomical.

[edit] Conclusion

Compressive, tensile, bending and buckling are the basic types of structural failure for construction elements. These are caused due to faults in design and construction. To mitigate these failures the structural engineer has to properly study properties of the structural materials, loads to be applied and the use of the structure to propose an appropriate material, adequate cross section and a proper structural system.

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